Extensions, garages and porches in a village near a market town often finish in a flat or low-pitched roof. They are simple to build, and they are the part of a house most likely to start leaking first.
Q2.1Which flat roof coverings are common?
Three do most of the work. Bitumen felt, laid in layers, is the traditional choice. EPDM is a rubber membrane, usually supplied as one large sheet with few joints. GRP is fibreglass laid in resin to form one continuous skin on the deck. Each suits particular shapes and budgets, and we explain which suits yours. Our flat roofing page sets out the options.
Q2.2What decides whether a flat roof drains?
Water must run off, not sit. BS 6229:2018, the flat roof code of practice, recommends a finished minimum fall of 1:80, with the design set at 1:40 so the finished roof still achieves it once the deck has settled. A roof with ponding water has lost that fall, and standing water wears out a covering early. Under Approved Document L, replacing a flat roof's waterproof membrane is renovation of a thermal element, so insulation joins the conversation whenever one is renewed.
Q2.3What do these coverings cost?
The table gives typical national figures per square metre from the guides named in its caption. They are not our prices. What your roof costs depends on its area, the state of the deck, how we reach it and which covering is chosen; the quote you receive after the survey gives one total. Felt carries the lowest price per square metre in the table and the shortest life, while EPDM and GRP cost more and last longer, so the lower price is not always the better value. If you hold another quote, see whether it includes VAT and scaffolding.