text: The Greek Ministry of Finance has now installed a green roof on the Treasury in Constitution Square in Athens. The so-called "oikostegi" (Greek – oiko, , meaning building-ecological, and stegi, pronounced staygee, meaning roof-abode-shelter) was inaugurated in September 2008.  Studies of the thermodynamics of the roof in September 2008 concluded that the thermal performance of the building was significantly affected by the installation. In further studies, in August 2009, energy savings of 50% were observed for air conditioning in the floor directly below the installation.  The ten-floor building has a total floor space of .  The oikostegi covers , equalling 52% of the roof space and 8% of the total floor space.  Despite this, energy savings totalling €5,630 per annum were recorded, which translates to a 9% saving in air conditioning and a 4% saving in heating bills for the whole building. An additional observation and conclusion of the study was that the thermodynamic performance of the oikostegi had improved as biomass was added over the 12 months between the first and second study.  This suggests that further improvements will be observed as the biomass increases still further.  The study also stated that while measurements were being made by thermal cameras, a plethora of beneficial insects were observed on the roof, such as butterflies, honey bees and ladybirds. Obviously this was not the case before installation.  Finally, the study suggested that both the micro-climate and biodiversity of Constitution Square, in Athens, Greece had been improved by the oikostegi.