Cost of a Flat Roof in the UK (2025)
A flat roof costs £40–£120 per m². A typical garage or extension flat roof (20–25m²) costs £1,500–£4,000 depending on material.
Flat roof material options
Traditional felt roofing (3-layer system) is the cheapest option but typically lasts 10–15 years. EPDM rubber roofing is durable, easy to install, and lasts 25–50 years — it is increasingly the preferred mid-range option. GRP (fibreglass) roofing is seamless, hard-wearing, and has a 25-year lifespan — ideal for areas requiring a clean, attractive finish. Liquid membrane systems are flexible and good for complex shapes.
Signs your flat roof needs replacing
Pooling water, visible cracks or splits, bubbling or lifting felt, and leaks inside the property are all signs that a flat roof is failing. Temporary repairs can buy time but a roof approaching the end of its lifespan is better replaced than repeatedly patched.
Cost Breakdown
All prices are indicative UK averages for 2025. Actual costs vary by location, specification, and contractor. London and South East rates are typically 20–35% higher.
| Item | Low | High |
|---|---|---|
| Felt flat roof (per m²) | £35 | £55 |
| EPDM rubber roof (per m²) | £45 | £75 |
| GRP fibreglass roof (per m²) | £60 | £100 |
| Liquid membrane (per m²) | £50 | £90 |
| Garage flat roof (20m²) | £1,000 | £2,500 |
| Extension flat roof (25m²) | £1,500 | £4,000 |
What Affects the Cost?
- ✓Roof area in m²
- ✓Material chosen — felt, EPDM, GRP, or liquid membrane
- ✓Whether the existing decking needs replacing
- ✓Insulation requirements — Building Regulations may require upgrade
- ✓Access and height
- ✓Location — London and South East rates are higher
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Post a Job — It's FreeFrequently Asked Questions
Which flat roof material is best?
For most homeowners, EPDM rubber or GRP fibreglass offer the best balance of cost, durability, and longevity. Avoid cheap single-layer felt as a long-term solution — it will need replacing within a decade.
Does a flat roof need planning permission?
Replacing a flat roof like-for-like does not need planning permission. If you are adding a roof terrace, adding rooflights, or significantly altering the appearance, planning consent may be required.
Can I walk on a flat roof?
EPDM and GRP roofs can handle occasional foot traffic for maintenance. Standard felt roofing should not be walked on unless designed for it. For a roof terrace, a specific trafficable waterproof system must be used.