Flat roofs - over extensions, garages, dormers and porches - don't last forever, and once the covering fails, patching only buys so much time. Replacement costs depend mostly on the material you choose and the size of the roof, and the cheapest option up front is rarely the cheapest over twenty years.
A small flat roof (a garage or porch) is usually £1,000-£2,500. A larger extension roof in rubber or fibreglass runs £2,500-£5,000+.
Typical UK Prices
| Job | Typical price |
|---|---|
| Felt (small roof / garage) | £1,000-£2,000 |
| EPDM rubber (extension) | £2,000-£4,000 |
| GRP fibreglass (extension) | £2,500-£5,000 |
| Warm-roof upgrade (added insulation) | +£800-£2,000 |
| Tear-off & dispose of old roof | £300-£800 |
| New fascias & trims | £200-£600 |
Materials Compared
- Felt (torch-on)
- The cheapest, and modern torch-on felt is far better than the old stuff - but still the shortest lifespan, around 10-15 years.
- EPDM rubber
- A single rubber sheet with very few joins. Hard-wearing, flexible, and good for 25-30 years. The popular mid-range pick.
- GRP fibreglass
- A seamless, rigid finish that looks smart and lasts 25-30 years. Pricier and weather-dependent to install.
- Warm roof
- Not a covering but a build-up with insulation on top of the deck. Costs more but cuts heat loss - often required by building regs on habitable rooms.
What Affects the Price
- Size and access
- Square metres drive the bulk of the cost; a high or awkward roof needs more access equipment.
- The deck underneath
- If the timber deck has rotted from a long-term leak, replacing it adds to the job.
- Insulation
- Upgrading to a warm roof adds cost but is often required when the room below is heated.
Repair or Replace?
- One small split or blister - a repair may do, see our roof repair cost guide
- Widespread cracking, ponding or a sagging deck - replacement is the better spend
- Old felt patched several times - you're throwing good money after bad
- Leaking into a habitable room - worth doing properly with insulation
Getting a Fair Quote
- Get the material, area and tear-off listed separately on the quote
- Ask what guarantee comes with the covering (EPDM and GRP often carry long ones)
- Check whether new fascias, trims and a warm-roof build-up are included
- For anything over £1,000, get two or three quotes
How Long Should a Flat Roof Last?
Lifespan is the real story behind the price. Old-style felt might give you ten years; modern torch-on felt a little more. EPDM rubber and GRP fibreglass are built to last 25 to 30 years, which is why they cost more up front but usually work out cheaper over the life of the roof. If you're staying long term, the dearer covering is often the better value - you replace it once instead of twice.
Signs Your Flat Roof Is Failing
Flat roofs tend to fail gradually, then suddenly. Watch for water that pools and never drains, blisters or bubbles in the surface, cracks along the seams, and any sag in the deck underfoot. Inside, look for damp patches on the ceiling below. Once the timber deck gets wet it rots, so a covering that's only cracked can quietly turn into a far bigger, dearer job if it's left.
Why Building Regs Sometimes Force a Warm Roof
If the room beneath the flat roof is heated - a kitchen extension or a converted space - building regulations usually require insulation when you replace the covering, meaning a warm-roof build-up rather than a simple recover. It adds cost, but it cuts heat loss and condensation, and it isn't optional on habitable rooms. A reputable roofer will flag this in the quote rather than skipping it.
Can You Walk on a Flat Roof?
Most flat roofs are designed to be walked on only for the odd bit of maintenance, not used as a terrace - standing water and foot traffic both shorten their life. If you want a usable balcony or roof terrace, that's a heavier, costlier build-up with proper structural support and a walk-on finish, so flag it at the quote stage rather than assuming a standard roof will take it.
Figures are typical 2026 UK ranges and vary by region and access. After a storm, run our storm damage roof checklist first. If a flat roof is leaking into the house right now, get an emergency roofer on the way to make it safe.