In many areas of the world, particularly tropical areas, the potable water supply system utilizes roof structures for gathering rain water which is directed to a collecting reservoir. Use of such systems are increasing worldwide. In certain areas of the world, population increases coupled with primitive or inadequate sewage treatment facilities have toxified the aquifer rendering well water unfit for consumption. In other areas, toxic wastes have poisoned the acquifer and/or underground wells again rendering well water unfit for consumption. In such areas, roof structures, particularly roof structures for large buildings, form an integral part of the potable water system.
Slate, shale, tile and bituminous roofing systems are unsuitable for collecting and directing potable water from the roofs of various buildings to collecting reservoirs. Besides water contamination, such systems are unsuitable as roofing structures for certain climates. Metal roofing systems are the only roofing systems suitable for use in all climates throughout the world.
The most common, long term, durable and easily assembled roof system which can be used for channeling water along a pitch roof of a large building is the Follansbee roofing system which is commonly known as the FRS system. One of the essential features of the FRS system, as currently produced, is the use of terne coated steel as the roofing material. The terne coated steel employed in the FRS system is a type 304 stainless steel coated on both sides with a terne alloy of 20% tin, 80% lead. The terne coated steel has inherent characteristics which assure functional longevity of the roof. Among such characteristics is the fact that the FRS terne coated steel solders easily so that pretinning or other special preparations are not required. This characteristic assures leakproof seams and joints. Importantly, the FRS terne coated steel is one of the most easily worked metals permitting on-site formation of standing seams without difficulty. The terne coated sheeting which is usually supplied in 26 to 28 gauge thickness (0.015 to 0.018 inches) is strong, takes shape and holds it but is easily worked. This is an important characteristic of the FRS system permitting not only easy installations but precise placement and forming of waterproof seams. Also, the FRS terne coated steel is not effected by alkali attack permitting applications in which contact with cement is possible and the terne coating is anodic to stainless steel which means that the terne coating will sacrifice itself to protect the core metal.
The aforementioned characteristics of the terne coated steel allows for a unique construction of either preformed or job site formed roofing pans, cleats, caps and other components which collectively form and have become widely known in the trade as the FRS system. Reference should be had to Boyd U.S. Pat. Nos. 4,934,120; 4,982,543; 4,987,716; 5,001,881 and 5,022,203 for a detailed discussion of the FRS system and many of the components used therein.
Despite all the advantages and inherent functional characteristics of the terne coat steel which permitted and enabled the development of the FRS system, terne coated steel is unsuitable for use in a potable water collecting system. This deficiency is not limited to terne coated steel but is applicable to all other metals currently used in conventional metal roof systems. For example, roofing systems formed from only stainless steel form standing seams by resistance welding, and the welding causes corrosion which can contaminate rain water and significantly reduce the life span of the roof.