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Flat Roof Cost in 2026: Felt, EPDM and GRP Prices Explained

Felt garage roofs from £1,000. EPDM rubber £1,200 to £2,200. GRP fibreglass £1,500 to £2,600. Below are honest 2026 guide prices for the flat roofs we replace every week across Windsor, Berkshire and South West London, then we price your actual roof free, in writing.

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2026 guide prices

Flat Roof Costs at a Glance

Guide ranges for the flat roof jobs we quote most often. Every roof is priced individually after a free inspection, and the written figure is fixed.

Job	2026 guide price	Notes
Flat roof patch repair	£150–£450	Splits, blisters and failed joints on an otherwise sound covering
Single garage roof, torch-on felt	£1,000–£1,800	Strip, deck check, three-layer felt system and trims
Single garage roof, EPDM rubber	£1,200–£2,200	One seamless sheet, typically 30 to 50 year lifespan
Single garage roof, GRP fibreglass	£1,500–£2,600	Rigid finish that takes foot traffic well
Extension roof, felt (15–25m²)	£1,500–£2,800	Includes upstands, drip trims and flashing into the house wall
Extension roof, EPDM (15–25m²)	£1,800–£3,200	Our usual recommendation for extensions: no seams, no naked flame
Extension roof, GRP (15–25m²)	£2,200–£4,000	Best where the roof doubles as a balcony or is walked on
Dormer flat roof re-cover	£600–£1,500	Small areas but fiddly details; access drives the price
Warm deck insulation upgrade	+£40–£70 per m²	Brings older roofs up to current building regs when re-covering
Replace rotten deck boards	Priced per board	Only visible once the old covering is off; agreed openly before work

Guide prices for 2026 assuming straightforward access. Larger or complex roofs are priced by measure after a free inspection. If your flat roof is on a garage or extension attached to a tired main roof, it can pay to look at both together: see the new roof cost guide. For pitched roof faults, start with the roof repair cost guide.

Felt vs EPDM vs GRP

Which Flat Roof Covering Should You Pay For?

All three systems work when fitted properly. The right one depends on what the roof does, not on the brochure:

Torch-on felt. The cheapest, and modern three-layer systems are far better than the felt that gave garages a bad name. Fine for garages, sheds and outbuildings. Typical life 15 to 20 years.
EPDM rubber. One seamless sheet, glued not flamed, so there are no joints to fail and no torch near your fascias. Our usual recommendation for extension roofs. Typical life 30 to 50 years.
GRP fibreglass. A rigid, wet-laid laminate that sets hard and takes foot traffic. The right answer for balconies and any roof you will actually walk on. Typical life 25 to 30 years.

We fit all three across Old Windsor, Egham, Surbiton, New Malden and the surrounding towns, so the recommendation is driven by your roof, not by the one system a contractor happens to sell.

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New flat roof completed by Seal Pro Roofing in Kingston

Flat roof replacement in progress by Seal Pro Roofing in Hampton

The honest bit

What Moves a Flat Roof Price Up or Down

Four things decide where your roof lands within the ranges above:

The deck. The biggest unknown on any flat roof. If the boards under the old covering are dry, the price stays at the bottom of the range. If water has been sitting in them for years, some need replacing, and we price that per board before touching it.
Details and upstands. A plain rectangle is quick. Pipes, rooflights, walls on two sides and abutments into the house all take time to detail properly, and the details are exactly where cheap flat roofs fail.
Insulation. Re-covering like for like is cheapest. Upgrading to a warm deck adds cost now and saves heat every winter after, and on habitable rooms building regs usually require it.
Access. A garage you can ladder is simple. A second-storey extension over a conservatory needs proper access, and the quote says so plainly rather than hiding it.

Every quote is written, fixed and free, with photographs of what we found. You can see exactly how we work on a real job in our Kingston flat roof case study and the Hampton re-roof and flat roof.

Spend once, not twice

Repair It or Replace It?

Repair when the fault is one split, blister or failed joint and the rest of the covering is sound. A proper patch costs £150 to £450 and buys years, not months.

Replace when the covering has crazed all over, water ponds across the middle, or the boards feel spongy underfoot. At that point patches are false economy: each one moves the water to the next weak point, and the deck keeps getting wetter underneath.

The most useful thing we do on a flat roof inspection is tell you which of those two your roof is, with photographs, before any money changes hands. If it does not need replacing yet, we say so.

“The team were knowledgeable and worked carefully to ensure everything was done properly. The roof looks solid and well finished. Very happy with the professionalism shown.”

Victoria Harris · Google review · ★★★★★ 5/5

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Get Your Flat Roof Priced Properly

Tell us what the roof is doing and we will inspect it, photograph what we find and put a fixed price in writing, free. Water coming in right now? Call us, we answer 24 hours a day.

07777 735785 01753 415 442

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Tell us about the job, we usually reply within the hour.

Prefer to talk? Speak to Cornelius on 07777 735785 or 01753 415 442

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FAQs

Flat Roof Cost Questions, Answered

How much does a new flat roof cost on a garage?

As a 2026 guide, replacing a single garage flat roof costs £1,000 to £1,800 in felt, £1,200 to £2,200 in EPDM rubber and £1,500 to £2,600 in GRP fibreglass, including stripping the old covering and checking the deck. The exact figure depends on the deck condition, which only shows once the old covering comes off.

Which is better, felt, EPDM or GRP?

All three work when fitted properly. Modern torch-on felt is the cheapest and fine for garages and sheds. EPDM rubber is a single sheet with no seams, which is why we recommend it for most extensions. GRP fibreglass is the most rigid and takes foot traffic well, so it suits balconies and roofs you walk on. We fit all three and recommend by roof, not by what we would rather sell.

Can a flat roof be repaired instead of replaced?

Often, yes. A localised split, blister or failed joint on an otherwise sound covering can be patched for £150 to £450. Repairs stop being worth it when the covering has crazed or ponded across its whole area, or when the deck underneath is saturated. We tell you honestly which side of that line your roof sits, with photographs.

How long does a flat roof last?

Properly installed, modern torch-on felt typically lasts 15 to 20 years, EPDM rubber 30 to 50 years and GRP fibreglass 25 to 30 years. Poor installation shortens all of them, which is why the fitter matters more than the material. Our work is covered by our company workmanship guarantee.

Does a new flat roof price include removing the old one?

Ours do. Every Seal Pro quote includes stripping the old covering, checking and reporting on the deck and timbers, the new covering and trims, and clearing everything away. If deck boards need replacing we price that openly per board before doing the work, never as a surprise on the invoice.

Do you charge to quote a flat roof?

No. Inspections and written quotes are free with no obligation anywhere in Windsor, Berkshire, South West London and Surrey. Cornelius, the owner, inspects the roof, photographs what he finds and puts a fixed price in writing.

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