Why do flat roofs leak?
Most flat roof leaks come from water that can't drain away, splits in an old covering, or failed edges and upstands. Because water can travel under the covering, the drip inside is often a metre or more from the actual defect.
- Ponding. A roof without enough fall holds puddles, which find every weak joint.
- Blistering, cracking and splits in older felt, especially at seams.
- Upstands and flashing where the flat roof meets the house wall — a very common source of leaks on extensions.
- Edge trims and outlets that have come loose or are blocked with leaves.
Water through the ceiling? The safety steps on our roof repairs page apply here too: catch the water, keep away from wet electrics and don't climb onto a wet roof.
What are the three types of flat roof?
Most UK domestic flat roofs are felt (bitumen), EPDM rubber or GRP fibreglass. They differ mainly in how long they last and how they're repaired.
| Type | What it is | Typical lifespan* | Repair cost (general range)** |
|---|---|---|---|
| Felt (bitumen) | Layers of bitumen membrane, the traditional option | 10–20 years | £100–£140 per m² |
| EPDM rubber | A single rubber sheet with few joints | 30–50 years | £120–£170 per m² |
| GRP fibreglass | Glass-reinforced resin laid on site, seamless but rigid | 25–40 years | £130–£180 per m² |
*Lifespans from a UK roofing guide (July 2026). **General ranges, not quotes, from Checkatrade's roof repair cost guide (October 2026): up to about 3m², ex VAT, excluding access.
How much does a flat roof repair cost?
A small patch repair is usually priced per square metre, roughly £100–£180 per m² depending on the covering, before VAT and access. Once the deck underneath is wet or rotten, or the covering has failed across the roof, re-covering the whole roof often makes more sense than patching.
The roofer will look at the deck as well as the surface: a soft spot underfoot means water has been getting in for a while. Ask for the quote to say clearly whether it is a patch, an overlay or a full strip and re-cover.
Repair or replace a flat roof?
Repair when the problem is local, such as one split, a failed upstand or a blocked outlet, and the rest of the covering is sound. Replace when the covering is near the end of its life, leaks keep moving around, or the deck is wet.
If the roof ponds, ask whether a replacement can improve the fall; that tends to matter more than the choice of material.
Is it the flat roof or the main roof?
On most houses, the flat roofs are on rear extensions, garages, porches and dormers. If the main roof is the problem rather than the extension, start with roof repairs. Either way, local Crawley roofers are a phone call away.