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Ecomerchant
2019 'must have' retrofit materials
This entry was posted in Ecomerchant and tagged retrofit products, net carbon zero, old house, refurbishment, retrofit, energy efficiency, poor quality buildings, energy efficient building, sustainable building, Approved Document Part L1A, Part L, building regulations on October 28, 2019 by ecomerchant.
In this article, we pick three standout retrofit products from 2019 and ask if their popularity could be linked to current and proposed regulations.
Are housebuilders selling us a lie?
This entry was posted in Ecomerchant and tagged planning regulations, affordable housing, new home, volume house builder, sustainable construction, environmental building, new homes, new build, self-build, housing developer, poor quality buildings, green building, energy efficient building, sustainable building, building regulations on August 29, 2019 by ecomerchant.
The planet faces an unprecedented series of environmental crises including climate change and the collapse of bio-diversity, yet for our construction industry and particularly the carbon-emitting housing sector it's 'business as usual'. Ecomerchant asked Sandy Patience, architect and editor at GreenSpec for his take on the paradox.
People don't buy, and the Government doesn't legislate for, future-proofed homes: Why not?
Why are we set on building houses that will cost owners and the rest of us dearly in the future? What follows, explores the complex reasons that have resulted in a perfect storm and the failure of the Government to provide adequate legislation.
Why are housebuilders selling us a lie?
My current walk to school alongside the new 'St. Michael's Fold' housing development provides me with an example of just how far volume housebuilders have travelled towards sustainable construction. The news is that it's not very far.
Some 30 houses are under construction. Brick and block with minimum cavities; lofts are waiting for the contractor to unroll the insulation; dummy chimneys and PVC windows surrounded by gaps through which you could slice a ping-pong ball. Each house is fiercely independent of its neighbours even if they are only a metre away - detached properties, of course, fetch premium prices. It's hard to detect evidence that the developer, or buyers, or planners, realise that we have a climate crisis and that new homes will be quickly rendered unfit for purpose.
Building new houses is a business designed to maximise profits and deliver shareholder value; customers play their part buy buying into this model, often due to there being too few viable alternatives. So begins the downward pressure on quality, as Dame Judith Hackett observed in her review of the UK housing market we are in 'a race to the bottom'.
The maximum wall area, using conventional materials, provided by detached houses ensures that they will lose heat in winter and badly overheat in summer. Given too, the rock bottom prices in the PV market and cheap hot-water collectors, it's surprising that the developer has declined to offer his customers their benefit. The on-site sales centre confirms that the houses are 'fully compliant' with building regulations. "Our buyers don't ask for any more than that." says the sales assistant looking sheepish.
For this particular estate, it gets worse. Sitting next to drainage ditches that criss-cross the landscape, this is essentially marshland incapable of sustaining much more than frogs. The site is so low that it's hard to see its survival much beyond a couple of floods from the nearby river as water levels rise. It's enough for an insurance man to break into a sweat.
Why are so many environmentally ill-equipped properties sold even before they're built? As in so many similar developments, the clue is in the hoarding size graphics at the entrance. 'Welcome to St. Michael's Fold'. St Michael is a local saint. A fold is where sheep are kept. The image is bucolic. Desirable. In the show house, the sales assistant shows us the 'period' features we can expect with our homes. It's another slice of ubiquitous 'Ye Olde England' signified by stick-on half-timbering, hanging tiles and 'leaded' lights. These are the bastard grandchildren of the Arts and Crafts movement.
Everything about how this development appears is fake. Fake history. Fake houses. Also fake too are the developer's claims that they have built homes for the future. No one is born to like country cottages or loathe terrace houses. The homes sell like hotcakes.
Why do we buy into Ye Olde England myth?
A typical bucolic English scene from which many new developments draw inspiration for their names, e.g. 'Bluebell Wood' or 'Meadow View' marketing terms designed to sell the lifestyle they have paradoxically helped to obliterate.
In contrast to most of the Continent, there's an association between Anglo Saxons and the detached house. Go to any suburb in the English-speaking world, be it Vancouver, Boston, Melbourne or Birmingham and you'll find detached housing built as default. Debate still runs about the origin of this, formerly English, phenomena. It derives at least from both the classic 'Englishman's Home is his Castle' icon and the need for differential from collective housing. Above all, it is a status symbol. For most people, it is the single most crucial signifier. Irrespective of the cost, the size and fitness for the purpose of being a home - it is the sign of having 'made it'. The Range Rover, another status asset, should have enough room to park in front.
The flight from industry
The Industrial Revolution gave us Blake's 'Dark satanic mills' - islands set in seas of Victorian industrial housing. Housing in an environment that we would describe today as toxic: Child mortality hit new peaks in the nineteenth century and in 1860s Liverpool, life expectancy sank to 25 years. No wonder then that a newly wealthy middle class chose to evacuate the city in search of AE Houseman's 'blue remembered hills' and the 'land of lost content'. There they built what they dreamed they'd lost. The pastoral fantasy reached its peak in 'Garden Cities' such as Letchworth, Welwyn Garden City, Bournville and New Earswick.
The 'Estate.'
For many, the collective memory of row upon row of straight Victorian 'two-up, two-down' terrace housing still haunts. Now relatively wealthy, we build the opposite. We cherish the cosy curves of the avenues (note: not 'streets'), closes, meadows, ways, rises and drives. The price we pay is a needlessly low-density sprawl of housing estates. From a conservation view it's a losing strategy - not only is it an inefficient use of land, but many of the houses will be ill-aligned to make the best use of the sun and provide protection from the elements.
A modern estate development typical of many across the UK
Will the Building Regulations protect us?
Expecting Building Regulations to set the standard for tackling Climate change would be a category error - the Regulations are not designed for engineering environmental policy.
Part L owes its origins, not to an environmental crisis, but an economic one. It wasn't until the 1960s that the Building Regulations expanded from protecting life and limb from bad construction to protecting our wealth. The introduction of statutory U-values for building envelopes in 1965 was only a gesture towards minimising energy wastage.
Come the 'Oil Crisis' of 1973; energy policy was revolutionised. Previously taken for granted, energy became a weapon in world politics. Dependence on oil turned into a liability - cutting off the flow could ruin a nation's economy. Nearly all Western governments introduced ranges of inhibitions on oil's use. The UK Government began requiring a U-value of 1.0 for external walls. Over subsequent years the U-value screw has tightened in line with oil and gas prices. Consequently, energy efficiency has significantly improved over the last 50 years, but it still falls far short of being a useful tool sufficient to realise any environmentally relevant standard.
Part L stands in an odd place. There's still the commercial imperative for fuel efficiency, but shouldn't it be the first legislative measure by which we prepare our building stock for global warming? If the industry was serious about climate change, wouldn't we have the appropriate regulation by now?
That, of course, would depend on Government policy.
The independent Committee on climate change (CCC) published the 'UK Housing: Fit for the Future?' in 2019. It condemns 'The way new homes are built (and that they) fall short of design standards. This is unacceptable.' The report calls for 'Immediate Government action … to ensure the new homes planned across the UK are fit for purpose, integrating the highest possible levels of emissions reduction' and that 'This will require an ambitious trajectory of standards, regulations and targets for new homes…'
So here's the problem: since concerns about global warming became public in the 1990s, fossil fuel-funded think tanks have framed it and other environmental issues as liberal and radical ideology designed to undermine capitalism. Pushing this agenda is a right-wing doctrine that claims that global warming is a hoax; that we shouldn't abandon coal, oil and gas.
The Conservative party already has form. The most crucial casualty of ideology was the plan to make new housing 'Zero Carbon' from 2016 onwards. Introduced by the Labour Government in 2007, it required new-build housing to be net-zero carbon through day-to-day running. Early in his premiership, Conservative Prime Minister David Cameron claimed that his was going to be the 'greenest Government ever'. It wasn't to be. That same Government, funded by the oil and gas sector, retreated from the 'Zero Carbon' commitment only months before it came into play. George Osbourne, the Chancellor, cited that constructing Zero Carbon Homes would be 'too expensive'. The Home Builders Federation added, helpfully, that '… new homes were already energy efficient under existing regulations'.
Of course, the 'extra expense' argument was nonsense. The building industry had a decade to bring construction up to scratch. Non-legislative standards such as the widely adopted Passivhaus showed that getting too demanding levels of energy efficiency added perhaps 1-2% to the cost price of a new home. Contemporary researchers at Cardiff University demonstrated that a zero-carbon house could even be built within the cost margins of social housing.
However, the door had been slammed shut. Other Conservatives expressed similar fears to the Chancellor:
'…we should not sacrifice Britain's economic recovery on the altar of climate change.' David Davis MP
'If you assume the worst then there is absolutely no point in spending any money trying to prevent inevitable climate change.' John Redwood MP
'People will die this winter because of the environmentalist obsession with the end of the world' Jacob Rees-Mogg MP
'…global leaders (are) driven by a primitive fear that the present ambient warm weather is somehow caused by humanity; and that fear – as far as I understand the science – is equally without foundation.' Boris Johnson MP
Beyond these shores are fellow travellers including one notorious conspiracy-monger who 'tweeted':
'The concept of global warming was created by and for the Chinese in order to make US manufacturing non-competitive.'
'This very expensive GLOBAL WARMING bullshit has got to stop.' President Donald Trump
Eccentric and irrational views are, of course, held by many people, but where climate change scepticism happens in Government, it becomes a weapon to thwart environmental protection.
Other measures withdrawn during this same period include 'The Code for Sustainable Homes; subsidies to onshore wind and solar energies; the 'Green Bank' as well as the 'Green Deal' designed to cut the energy loads in existing homes.
All across the board ministries rowed back on environmental initiatives - including the Department of the Environment which cut funding for climate change adaptation by 40%. Owen Patterson DEFRA's then-Secretary of State is a climate change denier.
With a policy environment this toxic, it is little wonder that any serious climate change legislation failed to appear.
After a brief hiatus, housebuilders could breathe again. It was business as usual.
Planning? What Planning?
The relationship between housebuilders and the Government is symbiotic. Both profit from their relationship with each other. A commitment to building homes has been the pledge of governments for over a century. Homeownership is a central plank in most election manifestos, and delivery of such is a key barometer of overall performance; Housebuilders, the other half of the association, have to do what they say on the tin. Their need to build houses correlates almost precisely with Government need to fulfil its promise to the nation. The whole is maintained through a balance applied through the Planning Acts. Local and central governments allow housing and the housebuilders build them. All is fine and dandy just so long as this judicious transaction continues.
A developed parcel of land with high density detached housing, typical of many developer-led projects, focus for the provider is to maximise land use and profit.
Government isn't a commercial enterprise, and housebuilders are not elected institutions. Difficulties occur when the Planning balance is upset by one or other of the parties. It might be on the one hand the need for unusually large numbers (as now) of homes and on the other the Government's need to satisfy the voting public. They see poor quality housing appearing on their green belts and cherished orchards. Added to the mix is the climate crisis as well as other acute environmental issues needing of robust policy to tackle.
Understandably, volume housebuilders resent change and 'unnecessary' legislation. Profit depends on construction efficiency and tight supply margins. Rather like other industrial products, houses are designed as commodities to be sold 'off the shelf'. Template-based rather than custom-built, each is designed to be easily constructed employing simple techniques and conventional materials. Imposed variations including changing legislation and Local Authority requirements invariably threaten the profit margins: new design templates are required, employees need training and the materials supply chain requires adjustment.
The climate crisis has been managed by successive governments according to respective views of the future and associated ideologies. The Labour governments of 1997 - 2010, responding to scientific advice, introduced the Climate Act in 2008. In 2006 they introduced the 'Code for Sustainable Homes' aka the 'Code' or 'CSH' and subsequently committed to the 'Zero Carbon Homes' initiative to be introduced through the Building Regulations in 2016.
The Code evolved from the excellent BRE-developed non-governmental Ecohomes standard. It was designed to encourage an ongoing improvement in performance across a range of environmental issues including energy, materials' impact, water efficiency, waste and pollution.
Use of the Code at Local Authority scale was wholly voluntary. It was implemented using Local Planning to impose aspects of the Code as planning conditions to achieve higher standards in new housing.
Regardless, in response to housebuilders' objections to 'obstructive' planning legislation and 'green taxation,' the Conservative Government progressively cut back Local Authority planning powers to control and direct new housing developments. Included as part of the 'bonfire of red tape' was the Code for Sustainable Homes, withdrawn in 2015.
Takeaways.
Don't wait for Whitehall.
However, we try to ignore/deny/avoid it; the elephant in the room is that the climate emergency has been politicised. To an innocent bystander, denial of the threat of climate change is right up there with the 'Flat Earthers' - incomprehensible. However, spend a little time in research, and it's easy to find how the fossil fuel industry and the anti-science movement fund climate denial lobbyists in both the US and the UK. Vested interests on both sides of the Atlantic, bend the debate to a point where progressive policy initiatives are stultified. In the UK, the PM talks in public of combatting shrinking bio-diversity as well as reiterating his predecessors call for de-carbonisation by 2050. Actual action on the ground: policy, legislation, workgroups even, there is none. Government is far the more useful tool in the box when it comes to tackling climate change; It's particularly painful then, to become aware that the current Johnson administration is blunted by ideology and compromised by its sponsors.
Leopards and spots.
Most volume housebuilders have no moral aspirations, so put-away your expectations. They build for profit in the here and now - there is no money to be made from anticipating the future. The only way they change is through legislation or by market forces.
Collective nostalgia throttles design for sustainability.
Developers will continue to build miniature fantasy houses just so long as we buy them. We are complicit in a self-deluding circle of marketing and buying. If the housing sector was the car industry, the lines would still be turning out Morris 1000s and Austin Allegros. Frightened about an uncertain future we hide in nostalgia. Breaking free is difficult.
Generally, we find ourselves in strange times. We're facing an existential threat more significant and more certain than anything humanity has faced before. In addition to climate change, we simultaneously confront reduced bio-diversity, diminishing resources and environmental pollution. It's the perfect storm, and we're still scrambling around to find some way of grappling with it. Ideologues disrupt science; The few technical developments making progress are piecemeal and uncoordinated; Our industries, including construction, are unprepared; Our political systems are ineffective vestiges from a time before environmental crises.
Never have we faced a crisis where lack of effective action by one generation can so completely screw-up the prospects of succeeding generations.
Inaction and prevarication over commitment to real change has brought public protest onto the streets as witnessed by the Extinction Rebellion protests.
So, what to do?
It's apposite that one way forward comes from the determination of one Swedish schoolgirl. Frustrated by the lack of political or popular will to confront the climate crisis, Greta Thunberg sat outside the Swedish parliament alongside a sign pronouncing that it was pointless for her to continue her education for a world that she wasn't going to inherit.
Stripped of the institutions we usually look to for action and reassurance; responsibility falls upon the individual. We must organise ourselves. "Since our leaders are behaving like children, we will have to take the responsibility they should have taken long ago." (Greta Thunberg addressing COP24, 2018)
We all have roles in the construction industry. Let's carry out those roles as if our children's futures depend on them.
Sandy Patience Dip Arch RIBA is an architect, journalist and speaker. He is the editor of GreenSpec at www.greenspec.co.uk - a site dedicated to delivering information about the design and building of Green Buildings and the Green Self Builder www.thegreenselfbuilder.co.uk a website specifically designed to educate and inform the self-build and custom-build market.
Disclaimer: The views, thoughts, and opinions expressed in the text are solely those of the author and do not necessarily reflect the official policy or position of Ecomerchant, its employee's or associates. This material is subject to copyright. Reproduction of the material may be made only with the written permission of the author.
The worst building you can build by law
This entry was posted in Ecomerchant and tagged housing warranty, small houses, housing developer, quality workmanship, energy efficiency, housing, poor quality buildings, energy efficient building, building fabric, heat loss, U Value, building regulations, healthy building, wood fibre insulation, Pro Clima, airtightness on June 20, 2019 by ecomerchant.
"We live in an era when our homes have the potential to be energy efficient, comfortable and affordable places to live, despite ever-increasing fuel prices. In the past, it could be argued that we didn't know how to achieve this but today we have no excuses. Yet, on the whole, we continue to build new houses to a pathetic standard, and our refurbishments commonly concentrate on kitchens and bathrooms, rather than investing to provide warm and pleasant places to live without ruinously high fuel bills." this is an extract from the blog of Ben Adam-Smith a campaigning documentary filmmaker and creator of a film about poor quality building called 'The Future of Housing ' there is a short clip below to help illustrate how poor quality construction can directly affect us all.
There is mounting evidence to suggest that buildings that are being designed to achieve thermal performance standards, including standards set out within the current UK Building Regulations, are in some cases consuming in excess of 70-100% more energy than the predicted values.[1]
Plus, some would say more worryingly, that the Building Regulations do not set an adequate base level of performance and facilitate the delivery of many buildings of poor quality into the UK housing market.
But….don't blame the Building Regulations they are not designed to deliver quality they are a set of minimum standards, all too often they are described, used and promoted as a benchmark; something to aim for: we must remove the presumption prevalent in the UK that they provide some form of performance guarantee……….they don't.
The Building Regulations contain 14 individual sections that, in their own words, 'contain the rules for building work in new and altered buildings to make them safe and accessible and limit waste and environmental damage'[2] nothing there about quality or performance then.
Within the Building Regulations, Part L is the section on 'Conservation of Fuel and Power' which relates to the thermal efficiency/performance of buildings. This is important because it covers the building's potential (target) level of efficiency and therefore comfort, it also has implications for running costs and is linked to (largely erstwhile) carbon reduction targets.
In particular section 43 of Part L deals specifically with a buildings air permeability, or airtightness, recognising this as a major factor in a buildings energy performance Interestingly the word "airtightness" wasn't even a word used in connection with domestic buildings, until it was introduced and formalised (through building regulations in the early 2000s) and has now become a key part of Part L, section 43 goes on to describe how this the means by which a buildings efficiency can be measured. Compliance with Part L is mandatory throughout the UK[3] it applies to new buildings and certain types of work in existing buildings and is there to enforce minimum standards of energy efficiency.
Airtightness is measured as m3/ (h.m2)@50Pa given as the flow of air (m3/hour) in or out of the building, per square metre of the building internal envelope at a reference pressure of 50 Pascal's between the inside and outside of the building. Current Building Regulations require 10 m3/ (h.m2)@50Pa, for a new build property, that's 10 cubic metres of exchanged air per hour at 50 Pascal's. This is a low standard by anyone's reckoning, examples of just how bad this is, in reality, are easily found. A new build terraced house with a tested result of 9.1 m3/ (h.m2)@50Pa passes Building Regulations but the tester pointed out (see clip below) that with external wind at an average of 20mph it would take just 6 and a half minutes to exchange all the heated air from within the building resulting in an expected increase in annual heating bills of around 50%.[4]
The short video below is an extract from The Future of Housing which clearly illustrates the point made above, it's well worth a watch, most people who watch this have exactly the same astonished and angry reaction as the owner of the house.
So how do you reduce wastage and increase the energy efficiency of a building, in simple terms insulate well and prevent leakage..... and that sits right at the heart of what needs doing.
In order to arrive at some basic elements that would apply to most building situations, we asked the technical team at Pro Clima if they could come up with a simple list of the "workhorses" of airtightness? Could they find six to eight products that would cover most eventualities? The answer came back as a resounding yes.
First two very pared down observations about airtightness.
Airtightness is effected on the inside of a building, on the warm or internal side of the insulation; the function is to prevent leakage. Variously called vapour check, vapour barrier, vapour control, or airtight membrane
Wind and weatherproofing is effected on the outside of a building the function is to prevent adverse weather penetrating the building fabric and reducing the insulation's capacity to perform and prevent deterioration in the building fabric. Variously called vapour control, breather membrane, vapour open membrane, vapour permeable membrane, vapour open underlay and sometimes additionally described as being diffusion open.
Together this 'wrap' for the insulated layer allows moisture control geared to our climate with protection from the elements on the outside and leakage prevention on the inside. The airtightness won't increase the U value of the insulation but it does ensure that the insulation functions to its optimum performance and more likely to achieve designed U Value. It cannot be overemphasised that airtightness and vapour control go hand in hand they work together to solve different problems.
Airtightness means designing and installing a continuous seal around the internal fabric of the external envelope to eliminate unwanted draughts. Once the airtightness layer is in place and sealed with flexible and durable tapes, seals and glues, it ensures that the insulation functions to its optimum performance, saving energy and drastically reducing carbon emissions for the lifetime of the building. The airtight layer also ensures that interstitial condensation risk is minimised, ensuring no structural damage from moisture, mould, rot and damp.
Here is the workhorse list
Internal airtightness membrane Intello Plus
External roofing membrane Solitex Plus
External wall membrane for use with timber frame Solitex Fronta
Universal jointing tape Tescon Vana
Sealing tape for windows Tescon Profil
Sealing tape for masonry and integrating into plaster Contega Solido
Six products that cover pretty much all the basic requirements, there are various accessories such as grommets, stoppers and glue that will be required but the bulk of the work is done with these six products.
How to use these products is neatly described in our "Making Airtightness Simple" [sic] guide available to download here
If you start with the basic principles and keep the products to a proven few then you will be less susceptible to industry 'noise' creating confusion or quandary over what product to choose. It would be disingenuous to say the there won't be times when technical advice is be needed and that is easily available through our technical support team. What it does mean is that for those manufacturers who do it well and make it look simple, take them on trust you are benefiting from years of robust and thorough testing and R&D arriving at a proven and purpose specific product. Their expertise should be your comfort.
Our thanks to Ben Adam-Smith at Regen Media for his quotes and permission to use a clip from the programme see the whole film by clicking here
[1] Lessons from Stamford Brook, Understanding the Gap between Designed and Real Performance, Evaluating The Impact Of An Enhanced Energy Performance Standard On Load-Bearing Masonry Domestic Construction, Partners in Innovation Project: CI 39/3/663, Report Number 8 – Final Report, Leeds Metropolitan University
[2] DCLG Policy paper 2010 to 2015 government policy: building regulation
[3] Check local variations for Scotland, Wales & Northern Ireland
[4] The Future of Housing Paul Jennings 2016
Sustainable, healthy building, are we getting it right?
This entry was posted in Ecomerchant and tagged comfort, natural building materials, energy efficient building, sustainable building, healthy building on May 22, 2019 by ecomerchant.
The most commonly accepted definition of 'Sustainability' was made in 1987 when referring to future world development: 'Sustainable development is 'development that meets the needs of the present without compromising the ability of future generations to meet their own needs'. The concept of 'Sustainability' in practice is a broad church within which a number of social, economic and environmental issues are included.
The building industry is usually responsible for around 10% of the UK economy and so represents a significant impact on areas of sustainability. The industry's key zones of accountability are: Global warming gases from the energy it uses; The quantity of material resources it extracts from the earth; The environmental damage caused by material extraction, processing and construction; And the damage to health caused throughout the extraction, manufacture, use and final disposal of building materials.
How does the building industry achieve higher levels of sustainability?
The industry can be more sustainable by adopting better principles and practices in the way it designs and constructs buildings. The way we design and build using the principles of 'Green Building 'can make a significant contribution, not only to reducing our collective impact on the environment but also to our health and wellbeing in the places we work and the homes we live in.
Like many other large industries, construction is very slow to change. Economically, the industry is notoriously volatile, so it's no surprise that change is seldom welcome or implemented. Most change is legislation-led through the Building Regulations and industry-related initiatives such as BREEAM; but some change is thanks to individuals and companies taking responsibility for reducing their own environmental impacts.
Sustainability, Quality and Self Build
The core of the construction industry is the 'volume' house-building sector. So critical is the role of the dozen or so companies that make up this group, that their economic role in the GDP (Gross Domestic Product), is regularly cited in economic reporting as the 'weather vane' of all industry. Key to their success is their efficiency of production. They buy materials and erect and sell homes on an industrial basis that maximises profits. That they manage to do this, whilst actually selling arguably poorly performing, indifferently constructed houses with abysmal space standards, is thanks to a well-oiled marketing machine that consistently succeeds at selling a premium on image, location and affordability. Notably, when the national economic output is bleak, so is that of the builders, who stop building until recovery. This chronic 'boom and bust' approach to housing is one of the reasons that the UK fails to meet the need for more homes.
In stark contrast to the anonymity and indifference of industry-produced housing, the self-build/custom build sector delivers for its members, well-built, well-performing, high quality and spacious homes. Increasingly their houses are made from materials and designs that put people, their health and their future at the centre of the process.
There are between 10 - 20,000 self-builds in the UK every year. This is less than 10-15% of all the homes built annually but may constitute as much as one-third of new detached homes - this compares with 60% in Germany and 80% in Austria where self-build is the norm.
Despite their number, self-builders have and continue to make significant contributions to advances in house design and technology. In particular, in recent years, they have been responsible for the dramatic uptake of 'Green' features such as renewable energy and low environmental impact building systems. Outside of the self-build market, these are features that take several years to filter through to commercial housing developments.
There is many a volume house builder who looks upon his self-build cousin with envy. Shorn of the profit motive, but instead equipped with a will to build exactly for his/her needs, the self-builder is at liberty to choose the type of construction and the materials that the building is made from. In particular, the self-builder is uniquely enabled to choose freely from the wealth of materials now appearing on the market that are not only of very high quality but also representative of a quickly growing market in the UK for 'sustainable' and healthy 'Green' products.
'Fabric first'
As part of the UK government's first initiative in 2006 to tackle climate change, it published a voluntary code requiring new homes to add renewable energy devices to the buildings. That it kicked off thousands of new businesses dealing in the installation of wind turbines, heat pumps and solar panels was probably no bad thing, but it was responsible for sending house builders off in the wrong direction.
Critics soon pointed out that the adding of energy-generating technology was usually doing not much more than covering for the poorly performing buildings they were attached to. The analogy to the policy was that of a leaking bucket of water: to keep the bucket full, it was necessary to keep pouring water into it - rather than fix the leaks themselves.
The code didn't change and was eventually eclipsed and abandoned. Instead, building designers and developers worked towards design standards of their own adoption. The most well-known standard, imported from Germany, is the Passivhaus standard which ensures that the way a house is built will deliver a heating requirement of no more than 15 kWh/m2/yr. This very low figure is achieved by careful design and the building fabric alone. For many already built Passivhaus homes, their heating systems have become largely redundant.
This emerging (in the UK) methodology of designing buildings to reduce their energy usage through building technology rather than adding renewable energy systems is known as 'Fabric first'.
Picture courtesy of Kithurst Builders Ltd. Passive standard family home in West Sussex built with natural materials. Roof sarking Steico Special Dry wood fibre insulation board.
Characteristics of a 'Fabric first' approach is:
High performance and high quantities of insulation.
Maximum levels of air-tightness.
Use of heat given off by the occupants and their cooking and electronic devices to help the heat the spaces.
Optimisation of natural ventilation.
Optimisation of solar gain through appropriately located windows.
Sometimes using the thermal mass of the building to absorb excess heat.
In addition to high degrees of energy efficiency, the 'Fabric first' method provides a comfortable environment that makes few demands of the building's occupants. Where renewable technologies place the reliance on the occupier to operate the sometimes complicated controls, a well-built energy efficient building has already done all the work for them.
What to look for when choosing 'Green' building materials
'Green' building materials are products that have a lesser environmental impact than other materials that might be used for the same 'job' in the building. Apart from environmental preferences, Green materials are also usually associated with high levels of performance and safe user-friendliness.
Of course, not all the building materials we employ have significant damaging effects on the environment. Those that do vary from severe to mild and to sort one from the other it's useful to consult the GreenSpec website which provides information about the environmental impacts of materials at www.greenspec.co.uk
There are usually plenty of alternatives, but the golden rule is to ensure that the products eventually selected can do the job demanded of them in a way equal to or better than materials they're replacing.
It is notoriously difficult to clearly identify materials with a lesser overall environmental impact. Experts can take a lot of time in examining and assessing the potentially wide range of environmental properties contained within even a single building product.
However, when specifying an appropriate product or material, these are some of the key low impact and beneficial aspects to look for:
Products that perform well and are easy to build with
Materials made from renewable crops such as timber, wool or hemp.
Products manufactured from abundant resources such as lime, clay or rock.
Products which minimise the use of fossil-fuel energy in the manufacturing process (embodied carbon).
Materials which, as a part of their function, improve a building's energy efficiency.
Manufacturing processes that don't pollute.
Materials that are safe to use and dispose of or recycle.
Products containing recycled materials.
The Healthy Home
Whether it be sleeping, eating, relaxing or working, we spend most of our day inhabiting our homes. Because of that time in a familiar space, we become adept at managing its environment. We are familiar with controlling lighting, heating and ventilation through simply throwing a switch or opening a window. Though the technologies have changed, the basic control actions are as they have been for generations.
Though the basic provision of light and warmth is unchanged, the contents of the air we breathe has altered over the last 50 years. We could now be dealing with a raft of possible toxins that if not sufficiently designed and built to avoid, could lead to serious health issues. Perhaps not surprisingly, these changes have been brought about through the way we build and the materials we use.
The principal drivers behind the need to improve the efficiency of our homes began with the oil crisis in the 1970s since when we have set out to reduce our dependence on fossil fuels. In the last decade, climate change has been added to the agenda. The combination of the two has had an aggrandising effect on building regulations and the techniques we use to design and build.
For our homes, the two main methods of addressing energy conservation are insulation and airtightness. We are used to using insulation in our walls and roofs, but now house builders have to learn the techniques of sealing openings in the building fabric to prevent warm air leaking out.
The result of sealing buildings could be that for many of us opening a window or just relying on the leaky nature of our buildings might not be enough to deal with the smelly, oxygen-depleted or damp air caused by everyday living.
Air contamination from materials we use in our homes is relatively new and owes its occurrence to the growth of synthetic materials. Ordinary products such as paints, floor finishes, timber-laminates, furniture, synthetic textiles, plastics and foams can emit a chemical cocktail including volatile organic compounds (VOC's) like formaldehyde, xylene, isobutylaldehyde, and organochlorides, aldehydes and phenols. Emissions from materials are known as 'off-gassing' and can result in higher, more toxic concentrations without suitable ventilation.
Sadly the most familiar aspect of an unhealthy building, damp caused by condensation, continues to blight modern housing. Most buildings show the effects of condensation to some degree – from water appearing on the glass of cold windows through to damaging mould found on walls and ceilings.
Asthma linked to inhabiting in these unhealthy conditions is on the increase, caused by damp and mould, house dust mites and chemicals in carpets and flooring materials.
The direct solution to damp air is adequate ventilation, but there is also a technique of building that has gained traction in recent years. The 'Breathing wall' is one that uses 'hydroscopic' materials and membranes together to allow moisture to pass from the interior through the wall to the outside air.
Summing-up, improving indoor air quality (IAQ) is achieved by:
Designing a ventilation strategy that can include simply opening windows through to providing mechanical ventilation. Above all, whatever strategy is chosen, it is vital that it is easy to understand and operate by the user.
Considering the use of 'breathing walls' that help migrate internal dampness through to the outside.
Avoiding materials that are suspected of off-gassing toxins.
Thinking holistically about combining techniques of reducing humidity and pollution and toxins - adding up to a whole that is more effective than the sum of its parts.
Using Green building materials from suppliers like Ecomerchant.
… and not forgetting the potential of indoor plants to absorb toxins and carbon dioxide
Top Tips For Going Green
Whether planning to build new from scratch or refurbishing, this is the time to incorporate sustainability into your project through design and the careful choice of materials; Getting it right will insulate you against spiralling energy bills, provide a durable long lasting healthy home and leave a lighter footprint on the earth.
The building industry generally acknowledges that self-builders build better quality buildings; In building their own homes, they are often keen to explore proven and beneficial systems that would not necessarily be part of a developer or volume house builder's package.
Picture courtesy of Baumit renders and plasters
So what are the key aspects of building to green standards?
Using enough insulation - most buildings are built with too little
The more insulation you incorporate into the walls, roofs and floors of your home, the more heat it will retain. Insulation is probably the main element to get right at the start, so it's important to ensure the appropriate materials are used in the right way and in sufficient quantity.
Design-in airtightness and ventilation – 'Build tight, ventilate right'
Fewer gaps in your home's structural envelope mean less heat lost. Good air tightness maximises the efficiency of the insulation and reduces fuel bills. With airtightness, ventilation is essential and needs careful design. Ventilation can be passive, mechanical or both.
Use the buildings thermal mass to best effect
The idea of thermal-mass is difficult to understand for most of us – so it's wise to get advice before using it. Materials such as stone, brick, terracotta and concrete can provide 'thermal mass'. Used with care, it can help moderate the internal environment throughout the day by absorbing excess heat from the sun or other sources and then releasing the heat back into the interior during darkness.
Design for overheating.
Increasingly hot summers are a climate feature we all need to design for. Use wood fibre insulation, particularly in rooms in the roof, but also in walls to slow down heat transfer from the outside. Think about using shading for windows exposed to the sun in summer, but make sure they're not shaded in winter.
Make the best use of natural light
Maximising the amount of natural light in your home reduces the need for artificial lighting. Windows are an essential element of the building's performance. Modern windows can be very efficient with whole window U values as low as 0.8W/m2K. 'Solar gain' can help heat the home.
Choose Green materials
Green materials have a range of features and benefits not usually present in synthetic materials; A majority are less polluting, safer and recyclable. Most too can significantly out-perform synthetic oil-based products in aspects that are becoming more important as the UK warms-up.
Structural systems - choose your system early in the design process
Most construction techniques can be adapted to meet high levels of energy efficiency, but some lend themselves more immediately to hitting the highest standards. This is where you will come across the expression 'Fabric first 'where the building contributes significantly to overall energy efficiency.
Some of the most popular systems for self-builders are:
Timber frame with timber, brick or render cladding
Monolithic clay blocks and render
Brick and block cavity walling
Cross-laminated timber (CLT) and cladding
Deploy renewable technologies only after your shell design is complete
Self-builders have led the way in terms of adopting renewable technologies to best effect, the golden rule here is to design the building to do the work, then match your energy needs to that level.
Thanks to our authors Sandy Patience & Will Kirkman: Sandy is an architect, journalist and speaker. He is the editor of GreenSpec at www.greenspec.co.uk - a site dedicated to delivering information about the design and building of Green Buildings. Will is a co-owner of Ecomerchant (a sustainable builder's merchant), writer and speaker and has been involved in promoting green construction for over 25 years.
2019 the year of healthy building
This entry was posted in Ecomerchant and tagged occupant health, sheathing, sarking, rigid wood fibre insulation, wood fibre, natural insulation, healthy building, Heat protection, Decrement delay, Breathable insulation, Flexible wood fibre insulation, Rigid wood fibre boards, Glulam, LVL, I Joists, Steico, wood fibre insulation, airtightness on March 20, 2019 by ecomerchant.
All buildings should be built with the occupant's health and comfort in mind, but much of what is built today falls short, we lack any regulatory requirement to deliver healthy buildings so it's down to customers to demand better, fortunately, there are plenty of people and businesses that can show us how.
A brief history of Building Regulation U-Values – with examples
This entry was posted in Ecomerchant and tagged Approved Document Part L1A, Part L, insulation, energy bill, building fabric, heat loss, blower door, air leakage, U Value, building regulations, airtight tape, airtightness on January 23, 2019 by ecomerchant.
In this post, we look at how U-Values within Building Regulations have changed over that last 50 years and how that has affected the thermal efficiency of a new build.
The theme of Building Regulations and U-Values is something we have commented on for many years, the Regulations, especially Part L1A is designed to set minimum standards for the conservation of fuel and power, but they are just that. For those who are looking to build energy efficient homes with good indoor air quality, the Regulations are simply part of the process as the design of such buildings will necessarily far exceed these minimum standards. We have looked at this subject many times in our blog, one of the most popular was an article that described 'The worst building you can build by law' subtitled Building Regulations are no guarantee of quality. However it is a fact that the Building Regulations do influence behaviour across the sector and can act as a lowest legal common denominator for any building, exceeding them for many developers has to be a considered choice, one that carries the certainty of return on investment so many still default to 'Regs compliant' only building. For this reason, we thought it interesting to look at how the regulations have changed over the past 50 years and how this has affected the baseline performance of our housing stock.
The theme for this article came from a piece originally written by Jon Davies and published on www.great-home.co.uk in this post we look at his observations and examples with comment and opinion by Paul Kalbskopf MRICS Senior Building Control Surveyor Wiltshire County Council and ATTMA Level 2 Airtightness Tester Paul Jennings of Aldas.
In his original article Jon Davies points out that the age of your house is a fairly reliable indicator of its likely thermal efficiency especially if no upgrades have been made to the fabric of the building – although many houses have been extended or otherwise significantly modified over the years. Over the last 50 years, the level of insulation required in Building Regulations has changed drastically to reflect both the need to reduce heating bills and increasing demand for comfort from homeowners. Below we consider how insulation levels have changed and what difference it has made to energy use.
Determining Factors on Space Heating Demand
When heating any space there are two critical factors that help determine how efficiently it can be done. The two factors also interact, typically in a detrimental way, and this has been a major cause of the "performance gap", about which so much has been written in recent years.
The first factor is the thermal efficiency of the structure, and within Building Regulations this is largely defined by U-Values for which there are target 'pass' values for the key elements: walls, floors, roofs & windows and doors. U-values are arrived at by calculating the combined individual lambda values of all the section components to arrive at an overall number, the number given in the Regulations will be the minimum required. It is generally accepted that the lower the U-value of an element of a building's fabric, the more slowly heat can pass through it, and so the better it performs as an insulator. The u-value is measured in W/m²K (Watts per square metre per Kelvin) the figure tells you how much energy is lost for every 1°C difference between the two sides of the material. Very broadly, the better (i.e. lower) the U-value of a buildings' fabric, the less energy is required to maintain comfortable conditions inside the building. If you have a material with a poor u-value then you can generally improve it with insulation - broadly speaking the more insulation you put in the lower the u-value although it's important to note that thermal bridging can ruin the performance of any installed insulation, make sure these are checked.
The second factor is air leakage, whether uncontrolled draughts or ventilation heat losses. Heating an insulated space may keep it warm but (and possibly more importantly) if the building leaks then the heat will be lost and the efficiency plummets. Too much air leakage and we lose our expensively heated air much faster than we need to, resulting in bigger heating bills and colder rooms. The circulation of fresh air to maintain good indoor air quality is essential, so the elimination of leaks coupled with controlled ventilation is one factor in determining an associated requirement within Building Regulations for a certain number of air changes per hour as houses get better insulated to reduce heat loss through the fabric then the heat lost through air leakage starts to become more significant.
Changes in u-values over the years
The table below shows the u-values required by Building Regulations for each building component in each decade. Building Regulations actually change more frequently than that (about every 5 years or so and each part of the regulations may be updated at a different time) but it gives a good guide to what has happened over the last 50 years. Highlighted cells indicate the first time the U-Value requirement for a component was strengthened.[1]
Building Regulations U-Value minimum standards 1970 – present*
*New Build Regulations Part L1A https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/540326/BR_PDF_AD__L1A__2013_with_2016_amendments.pd
See also Appendix 1. Below on 'Limiting fabric parameters'
Typical 1970s built terraced houses, despite the small size of the house they have front and back gardens with ample parking bays nearby. many of the houses on this estate also have separate garages.
The oil crisis of the 1970s forced the government to think seriously for the first time about reducing energy usage through regulation. The crisis drove changes in the 1976 Building Regulations which set minimum insulation levels for the first time. Before 1976 the standard cavity wall had not changed much since the end of the 19th Century, although solid, thermally less efficient, walls were still being built into the 1930s. Walls and ceilings were the first target areas with floors and windows following on later. Until 1994 you could still put a single glazed window in a house (u-value 4.8). When double glazing became a requirement the standard was set at 3.1 (what the double glazing industry could achieve at the time). In 2002 stricter regulations were introduced for windows for both new houses and also for replacement windows in existing houses.[2]
In his article 'Building Regulations and U-values: How have they changed?' Jon Davies gives a good example of the impact of the changes in u-values over the years, he provides the following example for a house built in each decade. He uses, in this example, a simplified 3-bedroomed two storey house, a rectangular box 10 metres long x 5 metres wide x 5 metres high (the pitched roof is not counted as part of the house as the floor of the loft is insulated).
Jon's example works through the consequences and comparative outcomes for each decade when building to prevailing Building Regulations, he also takes into account air leakage as described in the Regulations as this has an effect on the overall performance and subsequent heating cost. Needless to say, this is an 'on paper' exercise and as both he and Paul Kalbskopf points out later 'as built' will generally provide poorer results.
Jon assumes that the occupants try to keep all the rooms at 20°C for 15 hours per day whilst the outside temperature is at zero (0°C); that the floor is a suspended timber floor with clay underneath. The house is constructed with a cavity wall construction insulated to the standard prevailing at the time of build; he also assumes that air leakage is equivalent to an optimistic 1.5 air changes per hour (using this figure to compare ventilation heat loss with fabric heat loss).
Using the dimensions above gives the following for the simplified 3-bedroomed house:
Ground Floor Area: 50m²
Upstairs Ceiling Area:50m²
External wall area: 125m² (excluding windows/doors)
Windows/doors area: 25m²
House volume: 250m³
This simplified house is not that different to a house built today; today's average house has shrunk a little over the years in length to be 8.6m with a 5.2m width.
So what is the impact of improving u-values on the heat loss from this house?
Building Fabric Heat Loss by Decade Built To Building Regulations
Jon Davies makes the calculations in the table below in order to show the comparative difference that each change in building regulation has made. The calculations he uses are necessarily simplified based on pure fabric heat loss with no additional factors included.
He assumes the gas cost at 4p per kWh which means the occupants of the simplified 3-bedroomed house built to today's Building Regulations would be spending around 16% of what someone living in an unmodified 1970s built house would spend to mitigate fabric heat loss when the outside temperature was a constant 0°C.
A small terrace of 3 houses part of a 1980s development note how the front garden is now a parking space.
Jon's figure ignores the cost of heat loss due to air leakage which is worth briefly mentioning. The ventilation heat loss (air leakage) of a 1970's house would be about 2,475 Watts when the temperature outside was 0°C. That would add about 37kWh and £1.49 to the day's demand, taking the total heating cost from £5.46 to £6.95.
Moreover, the air leakage and insulation choices interact to give rise to a significant part of the performance gap mentioned earlier. Put simply, most of our bulk insulants (mineral fibre, glass fibre and more recently recycled plastic bottles or cellulose fibre) rely upon trapped air for the majority of the insulation they provide. If air is whistling through the insulation in a leaky house, most of the heat we expect to be retained by the insulation is actually being blown away! Especially in a loft with rolled out batts of fibrous insulation and warm air rising through it, the insulation might only be 1/3rd as effective as theoretically calculated.
A 2016-built house is expected to have less air leakage but it will not be dramatically better. A requirement to restrict air leakage was only introduced in the Building Regulations issued in 2002 (see updated 2016 edition, Approved Document L1A: Conservation of Fuel and Power in New Dwellings) - and even now Building Regulations airtightness requirements are sadly weak. Airtightness is checked by an air leakage test when portable fan equipment is used to apply a pressure difference of at least 50Pa relative to atmospheric pressure and the amount of air required to maintain this pressure is measured. But sample testing is still the norm when large developments are being tested, and the whole industry is well aware that those houses chosen for testing tend to get finished to a significantly better standard – draw your own conclusions!
For this example calculation, the Building Regulations airtightness target is 5m3/(h.m2) and the maximum allowable is 10m3/(h.m2) when tested at 50 pascals, roughly equal to the pressure of an external wind of 20mph. If you compare this with a Passivhouse air leakage is an order of magnitude lower at less than 0.6 ac/hr, which equates to approximately 0.5 m3/(m2.h) this being one-tenth of the standard target (or 10 times better than it) and one-twentieth of the maximum allowable (or 20 times better than it).
In a 2016 built house, it is likely that air leakage is a bigger cost than heat loss through the fabric. This is the big opportunity for future improvements in energy efficiency in Building Regulations. However, once you go much below 3.5m³/ (hr per m²) then other features should be added to the house design such as Mechanical Ventilation and Heat Recovery Systems (MVHR systems).
Jon continues to provide a little more detail about how the heat loss figures are calculated, below are his fabric heat loss workings for the 1970's house.
U-value and Fabric Heat Loss for a 1970s Built House
This tells us that ignoring air leakage, on a cold day 9,100 Watts or 9.1kW will be required to maintain a 20°C temperature. For a 15 hour period, this figure is multiplied by 15 to give 136,500 Watt-hours which is best expressed as 136.5kWh or kilowatt hours. Paying 4p per kWh for gas equates to about £5.46 uplift on the gas bill per day.
A modern mixed development from 2016. Note the small strip as a front garden compared to previous decades plus the houses have parking for one car or offroad parking.
Jon calculates the heat loss because of air leakage (ventilation heat loss) by multiplying the volume of the house (250 m³) by the air changes per hour (1.5) by the temperature difference (20°C) by 0.33 (energy required to heat 1m³ of air). This gives 2,475 Watts of heat loss that converts to an extra 37.12kWh of energy and £1.49 per day. Air leakage probably reduced as construction standards have generally improved between 1970 and 2016 but it is hard to quantify without air leakage testing on individual houses
Paul Kalbskopf adds that Jon Davies' excellent example has set out the theoretical requirements and costings for work carried out perfectly (as Jon notes). As we are all too well aware, the practical outcomes in this fallen world are very different. Practically all our buildings are prototypes, and, what is erected even in the controlled conditions of a test centre is rarely reproduced in the mucky reality of building sites affected by the daily changes of the UK climate.
This has been recently confirmed by work carried out by Colin King and his colleagues from the BRE (Building Research Establishment) who, by performing in-situ U-value tests on a range of buildings of all ages across the country, have revealed some startling results[i]. (The pre-1900's solid walled homes are performing twice as efficiently as we had assumed and the more recent, so-called low U-value elemental homes being compromised by poor construction standards; the 1940's/50's cavity-walled homes being worst of all!) Moreover, re-evaluation of condensation risk analysis methods, thermal storage capacity (and hence thermal inertia), microclimatology and air handling/air movement, should be causing us to consider buildings in a different light.
While a combination of materials in any given thermal element will result in virtually the same U-value irrespective of the order of the layers in the 'sandwich', it will have a dramatic effect on thermal capacity, interstitial condensation risk and ultimately, comfort and health factors.
The requirement for higher air-tightness requirements is a double-edged sword: whilst it reduces the energy loss due to uncontrolled ex- and infiltration, without addressing air quality, an increase of house dust mites, condensation, mould growth and ultimately rot can increase. While there are four different systems that may be used to comply with the performance specification requirements, the blinkered view of most designers and builders is to stay secure and comfortable in the old ways of doing things. Changing the way we do anything in our industry is akin to changing the direction of a fully laden supertanker!
Therefore, the suggestion in Building Regulations Part F section 5 of employing something other than locally operated isolated extract fans is just that – a suggestion. SAP calculations do not often allow for an air leakage rate of <3m3/(h.m2) at 50Pa, as most assessors will try to achieve design compliance at levels above that due to construction vagaries and quality. However, on pre-completion testing, if a figure of <3m3/(h.m2) is achieved and an MVHR (mechanical ventilation with heat recovery) system has not been installed, there is huge potential for problems as outlined above, as a retro installation will be inordinately expensive and disruptive.
Passive stack ventilation (PSV) only works if there is constant air input at a low level. Any visible openings are often closed as the occupier views the incoming air as a cold nuisance.
Mechanical extract ventilation (MEV) systems without heat recovery would appear to be literally missing the point if the priority is to maximise thermal efficiency, however, the fundamental reason to ventilate a building is moisture management (including odours) a critical factor in accelerated building decay.
The other major factor is that the standards set out in the Approved Documents are only minimum standards. Sadly most people – developers, builders, homeowners, see this as a maximum to be built up to, rather than a minimum to be built from. This attitude has sadly been disseminated throughout the industry by virtue of the major house builders who, in the name of maximising profit, build down to the minimum provisions required by Building Regulations, at minimal quality standards. Paul Kalbskopf comments that in his 40 years in the industry, he has rarely seen a multi-house developer do anything more than the (Criminal) law requires. The attitude is one of immediate expediency for short-term gain (profit for the shareholders) and for the foreseeable future, this looks set to remain unchanged
Here's another statistic that affects our comfort and our pockets, we are building smaller and smaller houses, smaller houses you would think will require less heat (not necessarily the case as we have set out above) but the size of the building and plot does have a direct bearing on occupant comfort and well being, according to research published by www.onthemarket.com new build homes today are often 20% smaller than homes built in the 1970s. Forty years ago there was room for a garage and two cars on the drive of most semis commonly built 12 to the acre. Today, buyers are lucky to get one parking space outside a terrace, built up to 24 to the acre.
Appendix 1.
Paul Kalbskopf notes, within the current Building Regulations[ii] there is now a requirement to insulate/ seal party walls to achieve U-values as set out in Table 3 of L1A, which vary from 0.0 to 0.5, depending on whether solid, filled or unfilled or sealed or unsealed. See Building Regulations Part L1A Online Version pages 14/15
Introduced in L1a 2014 is a requirement for swimming pool basins, if one is so fortunate, max. U-value 0.25.
Paragraph 2.33 alludes to Table 2, which gives the 'Limiting fabric parameters'. The vital sentence is the third: The shame is that the word 'likely' is used, rather than 'should' or 'must'.
Table 3 does give values to which we try to achieve, but, given we are dealing in area-weighted averages, there will still be scope for variations to be at the (poorest performing) limit.
Windows are a case in point where, for example, the insertion of an unsealed trickle vent into a hollow profile frame will make a mockery of the profile U-value and hence the 'whole window U-value' as given in Table 4.
The original article can be found at http://great-home.co.uk/building-regulations-u-values-how-have-they-changed/ January 19, 2016 Jon Davies
[1] http://great-home.co.uk/building-regulations-u-values-how-have-they-changed/ January 19, 2016 Jon Davies
[i] https://www.bre.co.uk/filelibrary/pdf/projects/swi/UnintendedConsequencesRoutemap_v4.0_160316_final.pdf
[ii] Building Regulations 2013 Edition Incorporating 2016 Amendments for Use in England. Approved Document Building Regulations Part L1A the Conservation of Fuel and Power. Online Version.
Further reading.
LABC Warranty Survey 2018 'What is the average house size in the UK?'
https://www.labc.co.uk/news/what-average-house-size-uk?language_content_entity=en
New build homes today are often 20% smaller than homes built in the 1970s. Forty years ago there was room for a garage and two cars on the drive of most semis, commonly built 12 to the acre. Today, buyers are lucky to get one parking space outside a terrace, built up to 24 to the acre.
Source www.onthemarket.com
Designing and building with natural insulation materials
This entry was posted in Ecomerchant and tagged acoustic insulation, wood fibre board, wood fibre batt, Steico Flex, heat loss, occupant health, natural insulation, healthy building, Heat protection, Steico, Ecomerchant, airtightness on November 2, 2018 by ecomerchant.
Why what we build from matters
The best buildings are life-enhancing and support our physical and mental health. Great design and healthy products enable the delivery of a healthy internal environment - meaning good indoor air quality, natural lighting as well as excellent thermal and acoustic comfort. In order to do this, we have to ensure we practise good decision making which requires an informed and holistic approach. Products that are low embodied carbon, natural, non-toxic, and healthy such as natural insulation have an important part in delivering better buildings.
But it's not only what a building is made of that contributes to a healthier living environment ventilation also plays a significant role. Where non-sorptive materials (i.e. in this instance ones that cannot absorb and release water as a vapour or liquid as opposed to sorptive ones that can) are used such as Polyisocyanurate (PIR) insulation moisture needs to be 'managed out' of a building to prevent poor air quality or potential condensation within the structure, non-sorptive materials are highly prevalent in modern construction methods meaning that the 'fabric' itself cannot help buffer and moderate the internal environment and ventilation is the only strategy to remove water vapour or pollutants. However, emerging evidence suggests that relying on ventilation strategies alone to provide healthy air inside low energy buildings is, in many cases, presenting significant risks to the health of occupants as well as the health of the building fabric.[i]
In order to build better, healthier more efficient buildings and taking a holistic approach the inevitable conclusion is that alternative strategies and materials should be seriously considered in order to achieve these elevated levels of performance. This presents a real opportunity to leverage design and natural building materials to deliver better standards. As insulation by volume is a significant part of any build cost, plus it has a direct correlation to building performance and occupant health, this is where the focus of building designers, architects, developers and owners is moving.
The 'Protexion Campaign' to promote natural insulation materials.
To address these issues and help promote the already growing market for natural insulation materials in the summer of 2018 Ecomerchant and Steico UK joined forces to launch a campaign to champion the benefits of using natural insulation products. The same principles that sit behind the promotion of natural insulation products were echoed by the Alliance for Sustainable Building Products and the Natural Fibre Insulation Group, the members of which, originally proposed that more work needed to be done to highlight the considerable benefits of natural insulation to a market that has largely ignored them in favour of cheap synthetic materials. Despite the clearly defined, tested and verified performance natural insulation worldwide it has not been taken up in the UK as much as in other countries. In the UK the default insulation materials are still mineral (glass) wool and foil backed Polyisocyanurate (PIR) however previous cost savings afforded by synthetic insulation have largely been lost and the price differential assumed before in favour of synthetic insulation has narrowed to the extent that natural insulation options can now be less expensive than synthetic ones plus the increase in timber frame and the desire for better airtightness is driving constructors towards natural solutions. Year on year sales in natural insulations have seen double-digit growth and a widening of the customer base to include modular construction, custom and self-build and social housing.
To help inform potential users of natural insulation materials the Protexion campaign developed a dedicated website www.ecomerchant.co.uk/protexion where you will find the wheel (illustrated below) the wheel has dynamic segments (links) e.g. health, fire and acoustic which click through to more information on each subject, you can also download wood fibre insulation certifications and find toxicology reports and environmental product declarations, this is the type of clear unambiguous information that allows us to make informed and better design choices.
The Protexion wheel, each segment links to the relevant role with supporting information, the wheel also links to accreditations, EPD's and toxicology reports. Click the image above to link to the Protexion site.
The appeal of natural insulation materials
How we select insulation needs to be about having a real choice and for specifiers to be equipped with the right knowledge to compare materials on a like-for-like basis plus different parts of the building will require different performance criteria no one insulation type will be the best for all applications.
To design a well-insulated building, you need to make informed decisions throughout all phases of a construction project to ensure your building performs as you envisage as mentioned above.
However, selecting the right insulation is about more than just reaching building regulation compliance or 'keeping in the heat'. It's about ensuring a building protects its occupants' entire well-being and comfort, the following list covers most of the core benefits and features of natural insulation and highlights the role they can play in delivering better, healthier and low impact buildings.
How well does insulation keep the heat out?
Summer overheating
High internal temperatures can cause respiratory or cardiovascular problems. Work by CIBSE and Arup suggests that most people begin to feel 'warm' at 25°C and 'hot' at 28°C. Their report also defines 35°C as the internal temperature above which there is a significant danger of heat stress. For vulnerable occupant groups, the impact of overheating can take effect much sooner with potentially much poorer outcomes.
Low fabric thermal mass leaves buildings more vulnerable to uncomfortably high, and in some instances, dangerously high internal temperatures in summer. This problem of summer overheating has been identified, by the NHBC and others, as a particular problem in buildings vulnerable to excessive heat gain with inadequate ventilation.
In the UK, thermal insulation to protect from the cold is essential, particularly given ever-increasing energy costs. However, as demand for the usable square footage of buildings increases, basement and loft conversions are the routes many now take. However, these parts of a home or office, are the spaces most prone to extremes in temperature. They, therefore, need more thought – i.e. how do you keep a space warm in winter but, for a loft, how to keep it cool come summer.
Compared with synthetic insulation materials, wood fibre insulation has a much higher density. This higher density means that natural insulation makes for a better heat buffer as the high midday temperature will only reach the internal side and be lost at night when the temperature is already cooler outside.
High internal summer temperatures are caused by heat from appliances and occupants, solar gain through windows and external heat penetrating through the fabric. It is the latter issue of penetrating heat where the thermal mass of natural insulation systems can delay the arrival of this heat energy so that it is emitted internally in the relative cool of the night. Perhaps good design with natural systems can hit a 'Goldilocks zone' of just the right levels of thermal mass and thermal conductivity.
Thermal comfort
Maintaining internal temperature around a comfortable mean is at the root of good fabric first low energy design. In lightweight constructions, some degree of thermal mass provided by the fabric helps to smooth out the internal temperature fluctuations which may be caused by heating systems or the opening and closing of windows and doors, for example. Natural insulation and systems tend to have high thermal mass relative to other types of insulation. This is due to the inherent physical properties of the cellulose or protein-based fibres and significantly enhanced by the presence of chemically bound water contained in these fibres. Water has a very high heat capacity which is twice that of concrete so its presence in natural fibres adds to the ability of the insulation to absorb heat energy.
How a building's lack of breathability is hurting our health
A breathable structure is one that allows the passage of moisture.
Those of us committed to the development of natural insulation products and systems view fabric breathability, or more accurately, the dry transport of moisture, as an important component in overall fabric performance. The ability of natural and hygroscopic materials to absorb and release water whilst remaining dry reduces the risk of interstitial condensation and ultimate fabric failure.
Natural fibres constantly adjust humidity levels away from extremes of damp and dryness helping maintain air moisture at comfortable levels, reducing the risk of both surface condensation and the negative health risks from moulds, mites and viruses. Of course, fabric breathability is not an alternative to a good ventilation strategy but should be considered as part of a robust and healthy building strategy.
In a report titled 'Health and Moisture in Buildings,' the authors conclude that 'these risks [moisture in buildings] combine with the other more clearly defined risks to the durability and value of the building fabric. It is relatively easy to see and to cost the damage done to buildings where moisture imbalance occurs. It is estimated that perhaps 70 to 80% of all building damage is due to excessive or trapped moisture' With such a large percentage of all building construction problems associated with water in some way, breathability is an essential component in preventing the accumulation of harmful water within the building's fabric. This is fundamental in reducing health risks from mould and mites that those suffering from respiratory illnesses such as asthma and chronic obstructive pulmonary disease (COPD) are particularly susceptible to.
For effective breathability, there are four essential components that need to be considered:
a moisture pathway
a driving force
a sorptive fabric
vapour control.
Natural fibre insulation is most effective as it suppresses potentially harmful water by binding and releasing moisture which helps regulate humidity levels as the moisture moves.
Easy-to-fit insulation
A well-designed building takes into consideration how a material performs throughout the building's entire life cycle. This includes ease of installation. Steico's wood fibre insulation is simple and easy to fit (either packed or friction-fitted), eliminating installer error, keeping construction programmes tight and costs low.
How insulation is fitted into or onto the building also has an impact on performance, poorly fitted insulation will allow the passage of air through the structure which can quickly strip out the heat from a building. Tests by Paul Jennings from Aldas featured in the documentary The Future of Housing demonstrated that a building with an air change of 9 m3/hour/m2 @ 50 pascals (Building Regs stipulates 10) when subject to a modest 20 miles/hr wind will take just 7 minutes to remove the heat from the building, what this shows is that regulatory compliance is not a good indicator of building efficiency, a guarantee of lower bills or occupant comfort. Minimising air movement through insulation is helped if insulation is designed to help restrict airflow, features such as tongue and groove profiles and dense fibre friction fit batts help to eliminate and reduce air pathways through the building.
Indoor air and occupant health
Creating and maintaining a healthy and comfortable indoor environment is a complex and difficult challenge. Temperature, humidity and carbon dioxide (CO2) must be maintained at safe and comfortable levels. Moreover, the introduction of pollutants such as particulates and volatile organic compounds (VOCs) greatly influences indoor air quality. A robust ventilation strategy is clearly critical to CO2 levels, but the building fabric can play an important role in helping to manage temperature, humidity and pollution levels. Sheep's wool insulation, in particular, can mitigate and absorb harmful indoor emissions including formaldehyde; the high levels of Keratin based in sheep's wool are known to react and eliminate formaldehyde test results[ii] showed that Thermafleece sheep's wool insulation absorbed 90mg formaldehyde per 1kg of insulation.
Internally generated air pollution
Finally, there is a very real and growing problem of indoor air pollution. The problem of poor external air is now well documented with a recent report from the Royal College of Physicians, Every Breath We Take, indicating that air pollution is leading to an estimated 9,500 annual premature deaths in London alone. The report authors recognise the current lack of focus on indoor air. Nonetheless, clients and designers can have significant influence over VOC and particulate levels by selecting low or zero emission products and systems.
A quick look at the issue of fire
All insulations will meet fire safety standards, but this is a minimum rating. Fire protection is a challenging topic and it combines materials (including fire testing and certification) and design in an effort to minimise risk, in all cases it is the mix of these two elements that will determine regulatory and performance compliance. There are also issues to consider in the use of fire retardants which evidence shows can be detrimental to human health[iii] However, there are some inherent properties of natural insulation that should be considered. Most natural insulation materials either resist combustion such as sheep's wool or 'char' quickly creating a carbon layer that helps resist the spread of fire such as wood fibre, additionally when burnt they will not give off toxic fumes such as cyanide as polyisocyanurate (PIR) or petrochemical insulation materials do.
Will the house be standing in 100 years?
Condensation is one of the costliest risks to buildings causing huge maintenance repairs and structural damage. Natural materials are better able to absorb and release water meaning it is better able to protect from and buffer moisture thereby becoming a key part of healthy living and building durability.
Comfort for occupants
Insulation improves comfort by moderating external effects and smoothing out variations. This applies to cold, heat and sound. One of the overlooked benefits of natural insulation is delivered by increased mass. This means it is better at reducing both overheating and noise pollution than synthetic insulation.
Improved well-being
Evenly warm walls deliver more radiant heat. Because people find radiant heat particularly pleasant, it is frequently possible to lower the actual ambient temperature without reducing the internal comfort. This leads to the positive side effect that reducing the ambient temperature by one degree means approximately a 5% energy cost saving.
Effective protection against mould
The humidity in the air will only condense on a cold wall, by creating warm walls, this condensation is eliminated. Without damp patches, mould is unable to grow. Mould is avoided from the outset.
Reduced air movement
Draughts caused by convection can be unpleasant. At uninsulated, external walls the air cools down, falls to the ground and flows to the centre of the room where it warms up and ascends again. This does not occur with well-insulated buildings. The cooling effect is reduced or eliminated. If the air is still, we do not feel these draughts and less dust is disturbed, providing positive side effects, particularly for allergy sufferers.
Cancelling out the noise for a peaceful night's sleep
The higher density of natural insulations - such as wood fibre - makes them better at reducing noise. Sounds external to the building, such as traffic or music, as well as those from within the building, through walls and ceilings are attenuated better by wood fibre than synthetic equivalents. In providing better protection from acoustic pollutants, occupants often report a building as being more restful and relaxing thereby encouraging better mental health.
When a building is well-designed and well-built, occupants should be at their peak comfort. With the average person spending approximately 80% of their lives in enclosed rooms, an occupant's well-being is imperative. Therefore, the products used to achieve this should cover all the issues affecting a building's construction, its impact on both its occupants and nature.
Buildability
During construction, the great British weather inevitably gets a building's shell thoroughly soaked before the roof goes on and it can begin to dry out. Using insulations that trap moisture and do not allow it to easily escape can cause damage to timber frame buildings and roof structures. Wood fibre sheathing and sarking boards are designed to be exposed to the elements during construction by adding in paraffin wax (candle wax) to the mix during manufacture. This means rain will repel, even when a board is cut, as the wax is 'through and through'. Additional protection should be considered if the wood fibre is too exposed to prolonged bouts of heavy rain.
Whilst wood fibre insulation can appear to absorb rainwater it dries very quickly afterwards without any detriment to the insulation material itself. Materials such as glass or mineral wool take up water in a similar way but are not able to dry quickly and should be removed if soaked to avoid damage to timbers.
Obviously, you should try and avoid soaking your insulation materials but if the worst happens you know that wood fibre will have no issues.
Wood fibre is clean and easy to use, there's no chance of toxic fibres or dust, in short, it's easier to handle and fit meaning that the installer tends to achieve a higher quality job. The snug fitting batts leave no gaps and the tongue and groove profile for the rigid boards ensures a tight secure fit. Disposal costs are less as natural insulation requires no specialist waste facilities.
Buildings should be considered not as standalone discrete entities, but as part of a system in constant and dynamic interaction with people and the environment. This interconnectedness means benefits, problems, solutions and consequences cannot be effectively addressed in isolation. If we adopt this broad and holistic approach, the benefits of natural insulation products and systems will come to the fore, and we should then expect the rate of market uptake to accelerate dramatically.
Authors note:
Thanks to the following for contributions to this article
The Alliance for Sustainable Building Products
The Natural Fibre Insulation Group
The UK Centre for Moisture in Buildings
[i] ASBP-Briefing-Paper-The-health-and-wellbeing-benefits-of-natural-insulation-products-and-systems
[ii] Eden Renewables ASBP Presentation Healthy Buildings Conference and Expo 2017, February 2017
[iii] greensciencepolicy.org Flame retardant chemicals in building insulation
What exactly is a VCL?
This entry was posted in Ecomerchant and tagged condensation risk, mositure mangement, Intello Plus, airtight membrane, building fabric, U Value, Breathable insulation, Ecomerchant, airtight tape, airtightness on September 28, 2018 by ecomerchant.
Vapour Control Layer (VCL) Explained
One of the most commonly used, and widely recognised, acronyms in construction is VCL, which stands for vapour control layer. A VCL is a critical building component designed to protect the building from potential degradation (or poor performance) by managing the passage of water vapour within a building structure. In other words, it is used to manage condensation risk. Condensation is formed when warm moist air condenses into a liquid on contact with a colder surface. A vapour control layer is typically installed on the internal side of the insulation to control the passage of warm moist air (water vapour) entering the structure. However, as a simple acronym, there is a problem because in most applications a specific level or type of performance is required, as a 'catch all' acronym VCL is wide open to error.
Condensation on the internal side of a window, showing that there was plenty of water vapour in the room, which has condensed onto the cold internal window pane. This is a good example of how much water vapour can be available to penetrate and condense within a building structure.
Unfortunately, and perhaps part of a wider misunderstanding, to many the term VCL is a synonym for polythene sheet, add in only a basic understanding of how condensation forms (as described above) and it is easy to see how the use of the term VCL can cause considerable confusion and anxiety. This is made worse by a large number of alternative terms such as vapour check, vapour permeable membrane, vapour barrier, vapour retarder, ACL, AVCL, vapour diffusion retarder, variable diffusion membrane, monolithic membrane, vapour diffusion barrier, airtight membrane, vapour tight membrane, microporous membrane, breather membrane all used to describe products covered by the acronym VCL …………………frankly it's no wonder people get confused by all of this. In this article, we will try to bring some clarity to the description and use of internal membranes to help you decide which type to use, where and how. A companion piece is in preparation about external membranes.
Broadly put there are 3 types of internal membrane.
Type 1: An impermeable barrier such as polythene, this lets nothing through. It's a vapour barrier or a vapour block, has only one function: to stop water, in all forms. An impermeable barrier cannot let water vapour back out of a wall when generated by solar gain - see point below - so this type of membrane has serious limitations in all but a few circumstances. Needless to say, the installation of an impermeable barrier needs to be 100% perfect for it to work. So, no holes, no gaps at the joints or overlaps, no accidental cuts or nicks and no major scrapes.
Type 2: A membrane that acts as an impermeable membrane most of the time but has some capacity to allow vapour transfer in certain circumstances. These are often described as a "vapour retarder" or a "vapour check" and they are designed to work under specific conditions where the inherent properties of the membrane can be relied upon. Since they only allow the movement of water vapour under these narrow and specific conditions, it is essential to apply them in appropriate situations.
Type 3: A membrane with variable permeability is often called an intelligent membrane. These are vapour control layers whose ability to allow moisture vapour to pass through depends on circumstances. Also known as variable diffusion membranes (VDM), most allow vapour movement in both directions, depending upon relative humidity either side of the membrane.
Some membranes in categories 2 and 3 can be described as breathable, you can read more about breathability here.
The choice of a membrane can largely be determined by location and build type so a vapour barrier (type 1) can be used under a concrete slab but an intelligent membrane (type 3.) is better to line the inside of a warm roof space.
The terminology used to describe membranes in buildings is hugely confusing and often ends up being concentrated into the single three letter acronym 'VCL' appearing on a drawing, but we know that VCL is a catch-all acronym it means nothing without some context or explanation, for example, we often notice people using the terms VCL and 'breather membrane' interchangeably, particularly with regards to pitched roofs. Whilst they have a similar purpose, there are a couple of important differences between the two.
So why do we need either? Quite simply – the vapour control layer is there to prevent condensation, which can cause a number of problems, including:
Structural damage due to rotting timber, whether this be a timber frame, joists or rafters
Insulation losing its thermal performance due to having absorbed the moisture
Mould, which not only looks unsightly but can also lead to respiratory problems and other health issues
People generate moisture inside their homes, through breathing, through cooking and particularly by washing themselves and their clothes. To prevent condensation, we need to eliminate this water vapour from inside the building. We also need to get rid of moisture that is outside the habitable zone but within the building envelope. This might be water from construction – fresh concrete, for example, takes many months to dry out fully - or perhaps rainwater that seeps through tiled roofs or is wind-driven up under the eaves.
Traditionally we have eliminated moisture by ventilation; for example, by ventilating the space between the insulation and the slate or tile on a pitched roof. However, studies have shown that ventilation directly above an insulation layer can reduce its thermal efficiency, which means more and more people are opting for an unventilated roof.
Some Definitions may help
Airtight layer- prevents the movement of air which may/ may not act as a Vapour Control layer
Vapour Control Layer- a material which can limit both movements of vapour by diffusion, and air movement
Breather Membrane- defined as a membrane with a vapour resistance less than 0.6 MNs/g situated on the external side of the insulation acts as a weatherproof layer whilst still allowing water vapour to be passed to the outside.
Understanding your walls, temperatures and condensation
With a plethora of membranes on the market, each designed to do a different job and behave in a subtly different way it is easy to be confused about which membranes are required to create a dry and airtight building structure.
Starting with the basics, when insulating walls you create a temperature gradient across them with the warmest being on the inside and coolest on the outside during the winter months. You can imagine a graph of the temperature showing a fairly steady decrease in temperature as you move closer to the outer surface of the wall.
When you take warm, moist air and cool it (as it will moving through a building structure) you find moisture condenses at a point known as the 'dew point' or 'condensation point'. This will typically be the intersection of an impermeable or low permeability surface with the temperature falling low enough for water vapour to become liquid. This is how damp accumulates inside the fabric of your walls or your insulation, to the severe long-term detriment of your building.
Why you shouldn't use a 'vapour barrier' (Type 1. Membrane) in your walls
Different construction and insulation materials cope differently with condensation. Some materials, such as masonry, can absorb and release it again once the weather warms without too much damage. However, when using vapour impervious insulation in timber frame construction, any condensation forming in the walls tends to be absorbed by the timber, a process that can cause rot. Additionally, during the winter months when this condensation tends to occur, driving rain may also enter the fabric of the building, further increasing moisture levels in walls. It is therefore very important to prevent this condensation process occurring in the first place, for the longevity of the building.
One further complication to the above process can be found in the summer months. The temperature gradient is often reversed and the higher temperature is found on the outside of the wall and the lower temperature on the inside. This creates a situation where moisture is driven inwards and condensation can form close to the inner face of the wall instead.
In the UK until relatively recently an impervious vapour barrier was used on the inner face of a timber frame and was thought to prevent condensation formation by simply blocking the flow of moisture-laden air through the wall. However, it has since been found that not only are vapour barriers regularly full of holes which let moisture through during the winter months, they also cause the accumulation of moisture inside the wall during the summer months. This was caused by the barrier preventing moisture from escaping towards the interior of the building.
Water vapour that has condensed against a VCL, in this instance a polythene sheet (type 1) used as a VCL over mineral wool and behind plasterboard. Damage can be seen on the timber stud. This occurred within 2 years of installation. Photo courtesy of SkamoWall.
The high humidity levels and warm temperatures found in these walls combined to form perfect conditions for mould and rot to thrive. This was problematic to both the timber structure, as it rotted, but also to the inhabitants of the building as mould spores are well known to cause respiratory problems and ill health.
Vapour barriers are still useful though. One of the few places above ground level where a complete vapour barrier should be used is in flat roofing when using foil faced PIR insulation. In this case, you need to lay a vapour barrier on top of your flat roof deck before you lay the insulation and your flat roof covering.
Using a vapour control layer to control condensation
The answer to keeping timber-framed walls and roofs dry is to use a layer to restrict the flow of moisture but not to try and stop it. In other words a VCL (or a vapour retarder). A VCL is always used as close to the inner face of a wall as possible and reduces the amount of moisture passing through the layer to low levels, ensuring only insignificant amounts of condensation occurring within the structure. Additionally, this will allow moisture that is driven towards the interior in the summer months to slowly pass back inside the building. This prevents the conditions for mould forming and ensures the longevity of the structure.
Vapour control can be performed very accurately by the many membranes available but it can also be performed at a basic level by OSB, whose vapour resistance (or vapour permeability) is similar to that of some membranes. The benefit of using OSB as a VCL is that it is far more robust than a 0.2mm membrane and does not require the installation of another layer into your timber frame structure if used internally. However, you will need to test the airtightness of the OSB before using it as there is some variation in air permeability. For guaranteed results either use an airtight VCL membrane, such as the ProClima Intello Plus or Constivap or a board such as Unilin Vapour Block or a liquid applied membrane such as Blowerproof. Blowerproof and Intello Plus are both BBA certified.
It is also advisable to try and minimise the amount of moisture that enters your building fabric during construction. Much of our construction timber, sometimes including expensive windows, roof joist assemblies and even SIPs panels, are commonly stored on site with little or no protection against rain, especially driven rain. Once wet, they can take a significant amount of time to dry out, contributing to the internal moisture load a new dwelling has to deal with. This can even delay and degrade the final stages of construction: for example, airtightness tapes on OSB have been known to come off during airtightness testing, not adhering properly because the timber is still too wet.
The latest type of VCL membrane is the 'intelligent' membrane, such as Proclima's Intello Plus membrane. These are very useful products that remain very vapour tight (low vapour permeability) during the winter months when it's important to try and prevent moisture from entering your structure from the interior. As temperature and humidity in the walls rises the pores in the membrane open and allow moisture to migrate towards the interior of the building. This gives the best of both worlds and ensures your structures remain as dry as it is possible to be.
Watch the video to see how an intelligent VCL works
Using a vapour-check or foil backed plasterboard as a VCL
Vapour control layers are always required whenever you insulate, irrespective of the insulation used. They should be used to form a continuous airtight layer and so all the joints and any penetrations must always be sealed with the appropriate airtightness tapes. Without good levels of airtightness the VCL does not work and moisture levels cannot be controlled inside the structures. Products such as vapour-check, foil backed or insulated plasterboard tend to act as a vapour barrier but with none of the joints or penetrations sealed. These products should not be used instead of a VCL or where a VCL is used.
Always refer to a qualified designer if in doubt or ask the manufacturer for technical and installation advice, we are always happy to answer any questions about airtightness or vapour control or point you in the right direction.
Thanks to Paul Jennings and Chris Brookman for their contributions to this article.
Paul Jennings has over 30 years' experience of airtightness testing, in the UK and around the world, and has been extensively involved in the delivery of onerous airtightness specifications in Passivhaus and other low-energy projects. He tested the first UK certified domestic and non-domestic Passivhaus buildings, both in Machynlleth, on the same day more than ten years ago, and recently led the team that used 8 sets of test equipment to carry out the most complex airtightness test carried out in the UK to date, on Agar Grove Phase 1, in London. He trains airtightness testers and pioneered the development and delivery of airtightness champions training courses. He has been instrumental in improving our processes and tools for achieving good airtightness, as well as training sealing operatives and delivering numerous CPDs and conference presentations to a wide range of building professionals on different aspects of airtightness.
Chris Brookman lives in a Passive house of his own design which he built based on his own life principles of low impact, low energy living and human health. Chris runs Back to Earth, is a recognised expert on green building and passive construction, he has written widely on the subject and is a keen blogger on the practical and technical aspects of delivering sustainable construction; Chris also curated the first online Wood Fibre Insulation course
Adhesive tapes: how do they work, what should they be able to do, and what can they do?
This entry was posted in Ecomerchant and tagged Ecomerchant, Tescon Vana, Pro Clima, construction tape, airtight tape, airtightness on August 9, 2018 by ecomerchant.
Why do adhesives stick?
Considerable lengths of various adhesive tapes are used when sealing buildings. A typical application is seen in the photo where tapes are being used to seal and connect an internal airtight membrane.
Adhesive tapes are used as bonding aids in a wide range of applications in the creation of airtight building envelopes. Several hundred metres of tape is often used on a single building! Adhesive tapes have become established as bonding agents for these applications (just as nails are the standard solution for timber structures). They have to fulfil their functions for a number of decades to ensure that the building in question fulfils the standards expected by the energy consultant and by the building client. This article provides an overview of adhesive technology and the key properties of adhesive tapes typically used in construction.
Aren't all adhesive tapes the same?
This illustration shows the various forces that act in an adhesive bonded joint. Cohesion refers to the internal strength of the adhesive. Adhesion refers to the sticking force to the subsurface. As a rule: the higher the adhesion, the lower the cohesion. An optimal balance between cohesion and adhesion is crucial for permanent adhesion. (See information box 1 with regard to adhesive tape tests on construction sites)
Adhesive tapes might appear similar or even identical at first glance: when you compare different products, they all have a backing material. Depending on the planned application for the adhesive tape in question, this backing material may consist of paper, plastic film or fleece. An adhesive substance has been applied to the backing, and this adhesive substance is covered by a protective sheet or protective paper on the underside of the tape. The various types of backing facilitate different areas of application. For example, a tape that can be used both indoors and outdoors must have a UV-stabilised backing; an adhesive window-sealing tape must have a fleece backing that can be plastered over. The difference is easy to recognise. However, if you consider the adhesive substance itself, the difference is not so easy to identify. A review of data sheets is often of little help in this regard, as they generally only specify limited technical data – and this data is also difficult to compare.
Adhesive tapes for the creation of air-tightness are generally manufactured using two main production methods. The majority (around 80 – 85%) are produced as dispersion adhesives. In this process, acrylates dissolved in water are applied to the backing material in a liquid state. Emulsifiers are added to the dispersion to ensure that the dispersion remains homogeneous and that the acrylates dissolve in water in the first place. The function of these emulsifiers is to attract water. The water is then evaporated in long drying tunnels later in the production process. The dissolved acrylates bond with one another, form long chains of molecules and become »sticky« as a result. The emulsifiers remain in the adhesive film, but no longer serve any purpose.
A more exclusive group of adhesive tapes is manufactured using a solids-based adhesive containing pure acrylate. This production technology is relatively new and more laborious from an engineering viewpoint compared to the process used for adhesive tapes with acrylate dispersions. The adhesive is applied to the backing material in the form of a viscous mass and the individual acrylate molecules are cross-linked by the controlled addition of energy in such a way that the desired adhesive properties are created.
Honey and stone, or adhesion and cohesion
Honey has high adhesion – it sticks immediately to every surface. However, its cohesion is low, which means that honey drops off the surface under the action of its own weight. Stone is the exact opposite: it has high inner strength, i.e. cohesion, but has no adhesion and therefore does not stick to surfaces.
Adhesion and cohesion can be demonstrated very well by comparing runny honey with a stone. Honey exhibits good adhesion and sticks to surfaces very well as a result. However, its inner strength (cohesion) is so bad that it runs off in drops under the action of its own weight. A stone has high inner strength, i.e. cohesion, but very low adhesion. Good adhesion is generally associated with poor cohesion and vice versa. A good adhesive tape results from an ideal balance between cohesion and adhesion.
Why do adhesives stick? Sloths, squirrels and geckos
These photos show how strength builds up over the course of contact time. An adhesive tape was employed here that can be used for interior air sealing and exterior wind sealing. The initial adhesion – after 20 minutes – can be seen on the left; the significantly stronger adhesive bond after 24 hours can be seen on the right.
Let us consider the interesting question of how and why an adhesive tape is able to stick things together. The bond with the substrate is achieved using various mechanisms. Sheeting or a pane of glass may appear smooth at first glance, but their surfaces actually look very different – with hills and valleys – when viewed under magnification. The adhesive flows around these structures and claws to the surface like a squirrel on a tree or grips the surface like a sloth wrapped around a branch.
If the adhesive is in direct contact with the surface, attractive forces – so-called Van der Waals forces – will result between the two elements at a molecular level. The closer the adhesive comes to the surface, the more these forces will come into play and increase the strength of adhesion to the substrate. A similar principle applies with the gecko, which is able to walk upside-down on smooth surfaces such as panes of glass. This is made possible by a large number of very fine setae (hairs) on the feet of geckos, which increase the contact surface and thus facilitate sufficiently strong adhesive forces.
Take your time: the build-up of adhesive force
It can take some time before an adhesive has flowed into a subsurface fully and established a strong bond with it. Adhesive strength is generally built up over a period of hours. The reason that all manufacturers recommend that their adhesive tapes should be pressed into place can be explained by the mechanisms described above: an adhesive must be brought into close contact with a subsurface to be able to flow around and surround it.
A drop of water brings clarity – The influence of surface tension
There is a commonly held myth that an adhesive should be able to stick to every surface. And if an adhesive bond doesn't hold as desired, then it's always the adhesive agent's fault! However, this assumption is false. Nobody would think of taking two pieces of sawn timber, applying wood glue to them, pressing them together briefly and then pulling them apart again immediately, and then saying that the glue was responsible for the fact that the bond didn't hold.
Surface tension of foils: the low-energy surface has few attachment points and a low surface tension. It is not able to pull the water drop out of its shape. The more attachment points there are, the more energy the surface has and the more the water drop will be pulled out of its round shape as a result. High-energy surface: The liquid spreads across the material.
The quality of a given bond is always dependent on the bonding agent, the subsurface and the method of applying the bond. The release films used are evidence that not all foils are suitable for adhesion: some adhesive tapes can be easily removed from their release films. On the other hand, there are films that tapes bond well too, but which then become detached under tension. Finally, there are also films that adhesive tapes cannot be removed from at all. The surface tension of membranes is responsible for all of this. This tension describes how well a given membrane can be 'wetted' by an adhesive – in other words, how well the adhesive can get close to the surface of the membrane to be stuck. The surface tension of a membrane cannot be seen, and this value is specified in data sheets by a few limited number of manufacturers.
Water drop test
Silicone paper: Surface tension: < 30 N/mm. Very poor surface wetting. Very hard to stick for this reason.
Weak wetting and a poor adhesive ability for this PE airtightness membrane: approx. 35 N/mm
Double-layered airtightness membrane: Very good wetting and good adhesive ability, as the surface tension is greater than 45 N/mm.
How can one estimate surface tension on a construction site? One possible method here is the water drop test: a drop of water is placed on the surface of the membrane and it is observed how well the drop of water spontaneously wets the surface. The greater the surface tension (surface energy) of the membrane, the greater the likelihood that the water drop will be pulled out of its "drop" shape. This indicates a stronger and more reliable adhesive bond with an airtight membrane.
Of course, this test does not provide precise information, but it has proven useful in practice over a long period. Membranes with a surface tension of > 40 N/mm are recommended for permanent airtight adhesive bonds. Membranes with surface tensions significantly below this value are often used in building practice. In order to supply the market with adhesive tapes that can still stick to these lower-quality surfaces, large quantities of resins are added to acrylate dispersion adhesive tapes, in particular. These resins stick aggressively to poor surfaces. However, the problem here is that resins can oxidise with oxygen, become brittle over their service lives and lose their adhesive strength. To prevent this from happening, it is recommended to ensure that adhesive tapes that only contain pure acrylates are selected.
As well as being used for adhesive bonds for membrane overlaps, acrylate adhesive tapes can also be used on joints to adjacent building components consisting of timber, stone, wood fibreboards, plaster and concrete. This is possible as long as the surface is generally even, free of dust and resistant to abrasion. If all three of these prerequisites are not fulfilled by a given surface, it can be pre-treated with a primer. Primers for acrylate tapes are applied in liquid form and differ from undercoats in terms of their mechanism. An undercoat penetrates deep into the surface and strengthens it. A primer for an acrylate adhesive tape is designed to penetrate into the subsurface and also to form a film on the surface that levels out any unevenness. These primers have proven themselves in practice. It is critical that the primer is suitable for the adhesive tape: i.e. one should always think in terms of overall systems.
Resistance to moisture – why are there differences?
Adhesive tape after storage in water for 24 hours: Top: a conventional acrylate dispersion adhesive tape, re-emulsified with water; the adhesive has lost its strength. Bottom: pure acrylate on a solid basis is absolutely water-resistant.
Nobody wants moisture on a building site, but regrettably the reality often very different! Adhesive tapes have to be able to reliably withstand the challenges of moisture after they are installed. The first protective layer is the backing material that is used. A film is clearly more resistant to water than paper. However, moisture does not always come only from the outside, but often from the subsurface too. In this case, the advantage of the external protective effect of the film is reversed, as the moisture cannot escape through the film and builds up instead between the adhesive and the film.
As already described, acrylate dispersion adhesives contain emulsifiers in their adhesive film after production. A characteristic of emulsifiers is that they store water, and they are still capable of doing this years later. If an acrylate dispersion adhesive comes into contact with water again, the adhesive re-emulsifies often assumes a white colouring and can lose adhesive strength. Pure acrylates are fully water-resistant, as they do not react with water – in this way, their adhesive strength is preserved.
See yee, who join in endless union – Durability: experience and laboratory tests
Cohesion adhesion test with 47 adhesive tapes: 40 adhesive tapes failed within two years in a long-term test with low loading.
Reference is often made to the positive experience observed over the last 20 years with regard to the durability of adhesive tapes. When we plan and build a house nowadays, clients expect the built structures and the materials used to have a service life of 50 years or longer. As a result, it is even more important when selecting adhesive tapes to take into account long experience in the marketplace alongside ageing tests that confirm the high durability of bonding agents.
Consistent rules are coming: a new standard for bonding agents will create a basis for comparison
The forthcoming standard DIN 4108-11 will specify laboratory tests that have to be carried out for all adhesive tapes. This will create consistent quality standards and provide a basis for users to compare products.
Presently, adhesive tapes are not regulated by standards and there are no uniform minimum requirements that have to be fulfilled by-products. The draft of DIN 4108 Part 11 that is soon to be published will fill this gap and specify uniform and comparable minimum requirements for adhesive tapes. This standard contains various tensile strength tests on standardised subsurfaces such as wood and membranes, as well as the possibility of having systems (membranes and adhesive tape) tested by manufacturers.
Many of the requirements demanded from adhesive tapes described above are formulated in this standard. For example, the tapes are pressed into place in a defined manner before conducting a pull-off test, and the test is carried out with a low pull-off speed so as to simulate the long-acting, low tensile stresses that occur in real applications in this test. Ageing will also form part of the scope of the standard. It is not yet possible to state exactly whether and when the standard will be introduced and become part of construction law. However, the standard will form a good basis for comparing adhesive tapes with one another and will help installers and project planners to make informed decisions.
Summary: permanent adhesive joints are only possible with good systems and the right handling
Soft adhesives perform better in the 'finger adhesion' test, as they are better able to wet the surface of the thumb. This can lead to problems in practical construction applications, as soft adhesives generally have low cohesion forces.
Actual loading in practice on site: the adhesive joint is subjected to low forces over a period
of years, so sufficient cohesive strength is important.
Permanent adhesive joints on construction projects are feasible and can achieve reliable performance; nonetheless, damage to structures often occurs when joints become detached. Knowledge about the fundamentals of adhesion technology and about the loads that will actually be acting in practice is crucial in order to be able to carry out reliable project planning and testing too. An optimal end result can only be achieved with good handling, a high-quality subsurface and a suitable adhesive tape. All three of these criteria should be carefully considered by the specifier and the energy consultant on site. Manufacturers who make statements about the surface quality of their membranes and about the production technology used in their adhesive tapes (solid acrylate or acrylate dispersion) and who offer long market experience, 3 rd party accreditation by reputable bodies (i.e. PHI, BBA, NSAI, BRANZ etc.) appropriate ageing testing and engineering support should be preferred over suppliers who provide little or no information about their products.
See the Pro Clima range of airtight tapes here
This article was written by Jens Lüder Herms, Dipl.-Ing. (FH), Jens trained as a carpenter and then studied construction engineering. He develops practical solutions for sealing buildings as part of research and development at Pro Clima.
Design elements that help prevent overheating
This entry was posted in Ecomerchant and tagged thermal conductivity, thermal diffusivity, heatwave, phase shift, warm roof, overheating, heat loss, natural insulation, Heat protection, Decrement delay on July 16, 2018 by ecomerchant.
The current prolonged spell of hot weather will have highlighted to many of us the susceptibility of our buildings to overheating.
The issue of overheating in buildings is a serious health risk, figures published on mortality rates during heatwaves make grim reading but still, our construction methods and building regulations fail to deliver buildings resilient to overheating.
In this article, we look at why this is important, how we can design for cooler more comfortable buildings and what to look out for when planning building work.
The World Meteorological Organisation definition of a heatwave is "when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5oC, the normal period being 1961-1990". They are most common in summer when high pressure develops across an area. High-pressure systems are slow moving and can persist over an area for a prolonged period of time such as days or weeks.
They can occur in the UK due to the location of the jet stream, which is usually to the north of the UK in the summer. This can allow high pressure to develop over the UK resulting in persistent dry and settled weather.
When was the hottest heatwave in UK history?
The scorching summer of 1976 was the hottest summer since records began. It led to a severe drought owing to the exceptionally dry conditions, although it is thought that 1995 was drier. In the summer of 1976, Heathrow had 16 consecutive days over 30oC from June 23rd to July 8th, and for 15th consecutive days from June 23rd to July 7th temperatures reached 32.2oC somewhere in England. But the single hottest temperature of 38.5oC was set on August 10th, 2003, the heatwave of 2003 led to the government creating a Heatwave Plan for England in response to the increase of deaths directly attributed to the heatwave.
You can read the Heatwave Plan here https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/711503/Heatwave_plan_for_England_2018.pdf
The current 2018 summer heatwave has seen the hottest day of the year so far recorded on Sunday, July 8th a temperature of 32.4oC (90F) recorded in Gosport, Hampshire.
Outdoor Temperature Thresholds – the effects on health
Statistical analysis shows that maximum daytime outdoor temperatures are a predictor of heat-related mortality.
In London, mortality starts to rise when the maximum daily external air temperature goes above 24.7ºC and has been estimated to rise by approximately 3% for every further 1ºC increase in external temperature. In other regions, the thresholds at which mortality starts to rise are lower. For example, the threshold for the North East of England is 20.9ºC.
Heatwave Plan Regional Threshold Temperatures for Heat-Health Watch Alert Levels 2-4.
Design considerations to prevent overheating - decrement delay and thermal buffering.
Anyone familiar with spending a hot summer's day in a caravan and then another in a stone house with closed shutters will appreciate the meaning of 'Decrement delay'. The inside of the caravan closely maps the rise and fall in external temperature to provide the familiar stifling effect on the occupants. In contrast, the internal air temperature of the stone house stays well below the midday heat, barely varies throughout the day and so provides relative comfort to those sheltering from the sun.
In the caravan, as soon as the outside cladding starts to heat up, output is detected within minutes on the inside face as most of the heat quickly transfers through the aluminium / lightweight insulation composite; whereas as the face of the stone wall heats up, the heat is absorbed by the stone and progresses slowly from the outside inwards. Hours later, some of that heat has arrived on the inside face of the wall whilst the remainder is released back into the cooler evening air.
The interesting, and often baffling, aspect of this phenomena is that the two materials can have very similar u-values - so that in steady-state conditions where heat applied at a constant rate over a period of time to the external face of both materials, there is an equally constant flow of (diminished) heat from the inside surfaces. Crucially though, for the purposes of thermal design, one material will start delivering heat to the inside before the other.
Heat transfer factors: Conductivity, Density and Specific Heat Capacity
But let's start with understanding how different materials cause different heat flow rates. What's actually happening within the materials? The answer relates to the dynamics acting between three variable characteristics whose values are unique to each material. The rate of heat transfer is determined by:
And of course, a further factor is the quantity or thickness of the material the heat is transferred through.
Thermal Diffusivity
Thermal Diffusivity ties the above factors together into an equation that measures the ability of a material to conduct thermal energy relative to its ability to store thermal energy. In effect, it is a measure of thermal inertia or 'buffering'.
The equation is:
Thermal diffusivity = thermal conductivity / specific heat capacity x density
Rigid polyurethane insulation has a thermal diffusivity of approximately 4.46 x 10-7 m2/s
Timber fibre insulation has a thermal diffusivity of approximately 1.07 x 10-7 m2/s
Copper has a thermal diffusivity of around 1.11 × 10−4 m2/s
In a material with high thermal diffusivity, heat moves rapidly through it because the substance conducts heat quickly relative to its volumetric heat capacity or 'thermal bulk'.
In the above three examples, we can see that heat races through copper while it moves more rapidly through rigid polyurethane than it does through timber fibre board.
Introducing the variable heat source - Periodic heat flow
'Thermal diffusivity' then accounts for the different rates of heat transfer through the variety of materials from a constant heat source.
However, when we look at the transference of the heat from the sun striking real-world roofs and walls, the heat source is not constant. The variability caused by such as the sun's passage through the sky is known as 'periodic heat flow' and, because the sun behaves, in the same way, every day ('diurnal'), its effects can be designed for.
Decrement delay
So, what is 'Decrement delay' and what can it do for us? In discussing its use we're looking to take advantage of the fact that some materials are slower at transferring heat than others. In buildings, the benefits of decrement delay are only realised where the outside temperature fluctuates significantly higher and lower than the inside temperature. So, ideally, if the maximum heat delivery to the wall or roof is at around midday, and because we can achieve a delay in heat transfer, it should be possible for that heat to finally penetrate the wall or roof to the interior of the building some time later when the inside of the building is relatively cool and the outside temperature has fallen as the sun goes down. At this point, the heat 'stored' in the wall can be released from the wall in both directions without overheating the inside.
The time it takes the peak temperature in the middle of the day on the outside of a wall or roof, to make its way to a peak temperature on the inside face, is called 'time lag'' phase shift or, more commonly, 'Decrement delay'.
By controlling decrement delay it is possible to control and prevent the overheating of a building.
A delay of between 8 and 12 hours might be considered optimum in normal conditions during extended periods of hot weather and cloudless skies up to 16 hours may be required.
It's worth noting too at this point that in a construction element containing several layers, the sequence of the material layers that heat passes through is also a factor in determining decrement delay. For example, in masonry construction where insulation forms one layer, locating it on the exterior of the masonry can significantly enhance the decrement delay effect.
The image below shows a roof make up with a variation in decrement delay (phase shift) achieved only by changing the insulation type, the overall section U value remains the same but the difference in phase shift is 8.8hours between the maximum at 16 hours and the minimum at 7.2 hours.
Image courtesy of Steico
How Decrement delay / Thermal buffering works on a rendered stone wall
Amplitude damping and the 'Decrement factor'
A stable indoor temperature is an aspect of thermal comfort. In conditions where the outside temperature fluctuates relatively widely, a constant indoor temperature is desirable. For example, an outside temperature might vary between 10ºC and 30ºC while internally it might vary just 1ºC above or below 20ºC. The fabric of the building envelope has effectively dampened the degree of oscillation.
The ability to attenuate the amplitude of the outside temperature to that of the inside is known as the 'decrement factor'.
It is calculated as f (the decrement factor) = Ti (the maximum swing from the ambient temperature on the inside) / Te (the swing in external temperature)
Example: From above, the peak to peak amplitude of the outside temperature is 20 degrees, and for the inside temperature it is 4 degrees.
f = Ti / Te = 1 / 10 = 0.1
Hence the closer the decrement factor approaches zero, the greater the effect the construction element has on attenuation. I.e. the smaller the decrement factor, the more effective the wall / roof at suppressing temperature swings.
The decrement factor is determined by the type and thickness of the materials that make up the wall or roof that the heat passes through.
(Confusingly, the same effect or 'amplitude suppression' is often expressed as a straight ratio. Taking the example above, the ratio would be 10:1 or 5:1 or more often just '10')
For a construction element containing several layers, the sequence of the material layers that heat passes through is a factor in determining decrement delay. For example, in masonry construction where insulation forms one layer, locating it on the exterior of the masonry can significantly enhance the decrement delay effect.
Calculating decrement delay
The response of construction elements to periodic cycles in temperature and heat gain can be quantified by using the thermal admittance framework as described in EN ISO 13786:2007. The framework also provides the basis for the CIBSE 'Simple Dynamic Model' for calculating cooling loads and summertime space temperatures (CIBSE (2005) Guide A: Environmental design).
Manually calculating thermal response simulations is not for the faint-hearted, but a number of programs are available to take the load - notably the freely available, Excel spreadsheet based 'Dynamic Thermal Properties Calculator' developed by Arup and distributed by the Concrete Centre. https://www.concretecentre.com/Publications-Software/Publications/Dynamic-Thermal-Properties-Calculator.aspx
The importance of decrement delay
Decrement delay will nearly always be more important in hotter climes than in the UK. An exception though is in timber/steel frame construction. One of the more common criticisms directed at lightweight construction is the lack of thermal mass - which can lead to the familiar 'caravan effect' above. Whereas masonry construction has the obvious benefit of 'heavy' materials such as brick and block, framed structures are typified by combinations of a cavity and lightweight insulation - leading to low thermal diffusivity and so little in the way of decrement delay.
Steico Special Dry Wood fibre insulation boards used on a pitched roof. Picture Courtesy Kithurst Builders Ltd
Until recently, insulation products were chosen mostly on the basis of a combination of their u-value and their thickness. Since the most commonly used insulation materials such as polystyrene, polyurethane and mineral wool had broadly similar densities and heat capacities, their decrement capabilities were relatively insignificant. With the increasing availability of wood fibreboard insulation materials in the UK, boasting comparatively high levels of diffusivity, designers can look forward to realising thermal performances more closely mapped to traditional masonry construction.
Some examples of materials
Don't building regulations already set a standard?
Approved Document Part L1A is designed to drive the conservation of fuel and power, rather than set thermal comfort standards. It requires housebuilders to make "reasonable provision to limit heat gains" in dwellings in order to reduce the need for mechanical cooling. Specific criteria or thresholds are not specified. The overheating 'check' in SAP Appendix P provides a means of demonstrating that reasonable provision has been made, but the calculation is not integral to the SAP rating and it is unclear what happens if a development fails the test.
"The dwelling should have appropriate passive control measures to limit the effect of heat gains on indoor temperatures in summer, irrespective of whether the dwelling has mechanical cooling. The guidance given in paragraphs 2.38 to 2.42 of this approved document provides a way of demonstrating reasonable provision." Criterion 3, Approved Document Part L1a
The Standard Assessment Procedure (SAP) is the Government's procedure for rating the energy performance of homes.
Designers and developers in the UK need to show compliance with SAP for each of the domestic units they are designing. It is not a design tool, but rather a compliance tool intended to produce an energy rating.
SAP Appendix P is a simplified check of whether the home could have an overheating problem. It uses regional average external air temperatures for the months of June, July and August, heat gains and fabric characteristics of the building in order to calculate monthly mean summer internal air temperatures. These are then compared to a table of threshold temperatures. For monthly mean internal temperatures below 20.5°C, overheating risk is predicted to be 'not significant', whereas for temperatures of 23.5°C and above, the risk is 'high'.
Issues with SAP
The temperature inside a home depends on many variables and changes throughout the day. Overheating risk during severe hot weather events cannot be calculated using monthly average temperatures. Neither can the impact of the Urban Heat Island effect or future changes in climate.
Housing Providers and experts consulted by the Zero Carbon Hub raised many concerns with SAP Appendix P. For example, it allows unrealistic assumptions to be included, such as that windows are constantly open, which make it too easy to pass.
SAP 2012 (Appendix P): Levels of threshold temperature corresponding to a likelihood of high internal temperature during hot weather.
We have to acknowledge that overheating is a problem to be avoided and that we don't need a heatwave to prod us into action, buildings can overheat for a multitude of reasons but the use of materials that help buffer heat preventing rapid transfer through the building can be used to substantially mitigate the risk. Typical areas that will benefit from such design are timber frame and lightweight structures, on a brick or masonry house this will usually be the roof. This is an important area to factor in heat buffering as it combines the warmest part of the house (hot air rises) with the largest solar collector on the building – the roof itself. Wherever possible design with overheating in mind, the Building Regulations do not require minimum standards for decrement delay and SAP is currently under review regarding overheating, so the choice to design and build to prevent overheating is one that rests solely with you.
BRE Overheating in Dwellings
Tackling Overheating in Buildings
Overheating - a growing threat that mustn't be ignored
Our thanks to Sandy Patience Dip Arch RIBA editor of www.greenspec.co.uk for material used in this article

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