Flat roof cost in Brighton in 2026 depends mostly on the size of the roof, the system you choose and the state of the deck underneath. Here are the ranges for garages, extensions and dormers.
Garages
A single garage flat roof, stripped and re-covered with a new deck: about £1,200 to £2,500 in torch-on felt or EPDM, a little more in GRP.
Extensions
A rear extension of 15 to 25 square metres with a new deck, upstands and trims: about £2,000 to £4,500. Add about £400 to £900 for each rooflight built in.
Dormers and bays
Small flat roofs on dormers and bays cost more per square metre because of the access and the edges: about £600 to £1,500 depending on height and size.
Felt, EPDM or GRP on price
Torch-on felt and EPDM rubber come out close on most roofs. GRP fibreglass costs a little more and gives a hard, walkable finish. The deck and the access make more difference to the total than the choice of system.
Why the deck matters
Laying new felt over a wet deck traps the water and the new roof fails early. We replace the deck every time we replace a covering, and it is in the prices above.
Get a real price for your roof
Ranges are a guide. The real number comes from someone looking at your roof. William comes out, shows you what is needed and gives you a free written quote.
Questions
How long does a flat roof take?
A garage or small extension is done in a day. One of our customers had her felt roof finished in about five hours.
What guarantee comes with a new flat roof?
Our 25-year guarantee on the workmanship, plus the manufacturer's guarantee on the system.
Can I go over the old felt?
We do not recommend it. Overlaying traps moisture in the old deck.