Flat Roof Build - Ups
EPDM rubber membranes are suitable for use in most flat roof systems. The finished roof should have a fall of at least 1 in 80 (1.25%) as recommended by Single Ply Roofing Association (SPRA) to ensure water run-off. There are two main roof build-ups for a flat roof, a warm roof and a cold roof.
A warm deck roof is the more modern roof build-up and preferable where possible. It is called a warm deck roof because the insulation is above the joists and main deck, meaning the entire roof structure is insulated (and warm). The benefit of this is that the chance of condensation within the roof structure is reduced. Unlike cold deck roofs, there is also no need to vent the roof void. If you are installing a warm roof over an existing roof, it is possible to leave the original roof covering in place to act as the vapour barrier as long as it is in good condition.
Cold deck roofs are the most common and traditional method of roof build-up and can be retrofitted where it is not possible to build a warm deck. Cold decks are so-called because the insulation is placed directly above the ceiling boards, and a cavity left between this and the roof deck. The air in this area is essentially outside and cold, so must be well ventilated to avoid condensation occurring.