Flat roof replacement for extensions, garages and dormers

A single split, a failed joint at an upstand, or one lifted edge trim on an otherwise sound roof is a repair. Replacement becomes the better option once the covering is cracked or blistered across large areas, once the timber deck underneath has gone soft or spongy, once ponding has been a persistent problem despite earlier fixes, or once a roof has had several patch repairs that keep failing in new places. At that stage, repeated small jobs cost more over time than renewing the roof properly once.

We inspect the surface, the edges and, where we can, the deck itself before recommending either option, and we will say plainly which side of that line your roof falls on.

There is no single rate per square metre, because what lies beneath the surface matters more than the area alone. We look at the size and shape of the roof, including corners, rooflights and changes of level, since every junction and penetration needs extra detailing. The condition of the deck is usually the biggest unknown: sound boards can stay, but soft or rotten ones have to be replaced before the new covering goes down, and this is only confirmed once the old covering is stripped back.

Insulation, upstands and edge flashings, the outlets and drainage path, and how the old roof and its waste are removed all form part of the estimate, along with the access the property allows. A written estimate sets these factors out rather than quoting a flat figure before the roof has been opened up.

The existing covering is stripped off and taken away, and the deck boards are inspected, with any that have softened or rotted cut out and replaced. Insulation is considered at this stage, since building rules may call for it once a roof is fully renewed, and it affects the height of the finished upstands and edges. A new waterproof covering is then laid to a proper fall, directing water to the outlets and gutters rather than letting it sit on the surface.

Upstands where the roof meets a wall are finished with a flashing, edge trims are fixed to throw water clear of the fascia, and outlets are checked for a clear run to the downpipe. The work is carried out in a suitable weather window, since the covering needs dry conditions to bond properly.

Flat roofs over rear extensions, garages and dormer windows all replace in broadly the same way, but each has its own weak points. A dormer meets the main pitched roof on three sides, so those junctions matter as much as the flat surface itself. An extension roof often meets the house wall at a single long upstand, which needs to be properly flashed. Garage roofs are frequently the oldest and most neglected on a property, and are a common candidate for full replacement once the deck has deteriorated.

When comparing estimates, check that each one covers the same scope: full strip of the old covering, an allowance for deck repairs if more damage is found, insulation, upstand and edge detailing, outlet work and waste removal. A lower figure that skips an allowance for deck repairs, or that proposes laying over a wet deck, is a false saving. Ask what happens if the boards turn out worse than expected once the roof is opened up.

Rowan Roofing is family-run, based in Cardenden, Fife, trading for 16 years with over 50 years of roofing experience in the family. We cover Edinburgh, Perth, Dundee and the surrounding area, travelling up to 50 miles for the right job. Call 07508 571291 or send details and a photo through our contact page, and we will arrange a visit before putting anything in writing.