Flat Roof Condensation Risk

We ve been talking to ian dryden business development manager at sig roofing about an increasing concern he has for flat roofs built in the 1980s and early 1990s and incorrectly refurbished roofs which appear to be leaking but they aren t.

Flat roof condensation risk. A flat roof should be designed to minimise condensation and a condensation risk analysis should be undertaken taking into account positioning of insulating materials vapour control layers ventilation thermal insulation and the choice of materials. However doing so increases the risk of condensation forming on the elements not surrounded by insulation such as cold roof decks. There are two forms of flat roof construction which can reduce the risk of condensation forming. Flat and low slope roof designs to avoid moisture condensation problems flat roofs call up a whole new breed of building moisture problems how to avoid moisture traps under flat roofs avoid mold rot caused by moisture trapped under un vented flat roofs questions answers about the cause cure prevention of moisture problems in flat roofs and similarly hard to ventilate structures.

For a flat roof construction be it a cold roof a warm roof or a warm inverted roof the calculation method for year round condensation risk set out in bs en iso 13788 known as the glaser method is almost always sufficient. This type of roof has normally been used over small extensions to dwellings using timber joists and plywood deck. As long as the roof accords with good practice then a more complex calculation method should not be necessary. Nowhere does it support the design and construction of hybrid roofs.

Designers should therefore take a cautious approach and adopt fail safe solutions. To that end the standard lists three acceptable scenarios for the placement of flat roof insulation. Cold roof warm roof inverted roof. This problem may become more common as existing buildings are altered to become eco friendly.