Flat roofing in Walmley

Walmley has more flat roofs per street than anywhere else we work, because that is how the 1960s and 1970s estates were built: a flat-roofed garage, often a flat porch, and — from the 1980s onward — a flat-roofed dormer bolted onto the back to get another bedroom. Nearly all of it went on in three-layer bitumen felt, and nearly all of that felt is now long past done.

This is the one job where we are unambiguously on the side of the modern material. We are traditionalists about slate and lead and mortar mixes. We are not traditionalists about felt. A fibreglass or EPDM covering will outlast the felt it replaces several times over and it is not a close call or a matter of taste.

The Walmley wrinkle is the deck. A lot of these garages were decked in chipboard, and fifty years of felt failing slowly above it means the board underneath is often soft — sometimes soft enough that you would not want to stand on it. Putting a twenty-five-year covering onto a deck with five years left in it is money set on fire, so we check before we quote, and if the deck is going we say so even though it makes our number bigger than the man who did not look.

For the choice: a plain rectangular garage is an EPDM job, because the whole roof goes on as a single sheet of rubber with no joints in the field at all. A 1980s dormer, with its cheeks and upstands and awkward junctions, is a fibreglass job, because GRP cures into one continuous piece and there is nothing at those junctions for water to find. Different roofs, different answers.