Flat roof cost in Brighton runs mainly on three things: the size of the roof, the system you choose, and how much of the deck underneath needs replacing. These are 2026 budgets for the roofs we lay most.
By roof size
A porch or bay top is from about £900. A dormer flat roof is about £1,200 to £2,500. A single-storey rear extension of 15 to 20 square metres is about £1,800 to £3,500. A double garage is about £2,000 to £4,000.
By system
Torch-on felt is the most affordable and very tough. EPDM rubber costs a little more and goes down in a single sheet. GRP fibreglass is at the top of the range and gives the neatest hard finish. On most extension roofs the difference between them is a few hundred pounds.
The deck is the big variable
If the boards underneath are wet or rotten, they come up and a new OSB deck goes down. That is the single biggest thing that moves a flat roof price, and it is why we check the deck before we quote.
Extras
Rooflights and lanterns, new insulation to bring the roof up to current standards, new fascias and gutters, and scaffold on taller roofs all add to the price and are listed separately on the quote.
Get a real price for your roof
Ranges are a guide. The real number comes from someone looking at your roof. Michael comes out, shows you what is needed and gives you a free written quote.
Questions
Which flat roof lasts longest?
Laid properly on a sound deck, all three last decades. GRP and EPDM have no felt laps to fail; torch-on felt is the toughest underfoot.
Is there a guarantee?
Yes. Every new flat roof we lay carries our 25-year guarantee in writing. Prime West are Firestone approved installers.
Can I walk on it?
For maintenance, yes. For a roof terrace, tell us at the survey so we specify the right system.