Chapter 1: Why does the flat roof on our Bracknell new-town house keep leaking in the same corner?
What we find
Bracknell grew fast after 1949, and builders of the 1950s and 1960s used flat and low-pitched roofs freely on garages, rear extensions and porches. Those roofs were usually covered in bitumen felt or mastic asphalt over a timber or concrete deck. A repair has probably been laid over an earlier repair, and each layer adds weight and traps moisture in the one beneath.
A leak that comes back to the same corner nearly always has a fixed cause. The usual suspects are an upstand (the short vertical edge where the roof meets a wall) where the felt has pulled away, a flashing that has lifted from the brickwork, or a hollow where the deck has dipped and water now stands. Inside, you may see a brown ring on the ceiling that dries out in summer and grows again in autumn.
What we fix
We start by finding where the water really gets in, which means lifting the top layers at the suspect corner and checking the deck below for soft or darkened boards. If the deck is sound and the covering is sound elsewhere, a local repair is the honest answer and we say so. If the felt is blistered right across the roof, patching only moves the leak, and a new covering is the better spend.
A replacement means stripping to the deck, renewing damaged boards, adding insulation to current rules and fitting a single-piece membrane. EPDM is a synthetic rubber sheet and GRP is glass-reinforced plastic, laid wet and cured hard. Typical UK ranges per square metre, supply and fit, are felt £60 to £100, EPDM £80 to £120 and GRP £100 to £160; your fixed quote follows the survey. Replacing rather than overlaying a flat covering can bring the insulation upgrade in Approved Document L into play, so we handle the building control side. Our flat roofing page sets out the choices.