Flat roofs on extensions, garages and dormers rarely fail all at once. Instead, they tend to develop small problems — a soft patch here, a slow drip there. These build up over a few years. The question homeowners in Richmond upon Thames ask us most is simple. Is it worth repairing, or should we just replace it?
When a repair makes sense
A repair is usually the right call when the damage is small and localised. Common examples include:
- A single blister or split in the membrane, caught early
- A leak at a flashing detail (where the flat roof meets a wall or chimney) rather than across the whole surface
- Ponding water in one corner that a repair, or better falls, can resolve
- A roof that’s otherwise structurally sound and under 10–15 years old
Because a targeted repair only deals with the affected area, it’s almost always the cheaper option upfront. It can also buy you several more years of service. That’s real value from a roof that still has life left in it.
When replacement is the better investment
Replacement tends to make more financial sense once a roof is showing its age across most of its surface, not just in one spot. Warning signs include widespread blistering, multiple leaks in different places, or a felt roof that’s visibly cracked and brittle. If you’re patching the same roof every year, however, you’re likely paying more in repair costs. Over time, that adds up to a long way toward a proper replacement.
Material choice matters here too. As we cover in our comparison of EPDM, GRP and felt, a modern EPDM rubber membrane can last 40–50 years. A traditional felt roof, by comparison, lasts just 15–20. As a result, a full replacement now can mean far fewer repair calls over the years that follow.
What it costs
For context, a typical 25–30m² garage or extension flat roof costs roughly £1,200–£3,500 for felt. EPDM rubber runs £1,800–£3,200, and GRP fibreglass £2,400–£4,200, according to Checkatrade’s 2026 flat roof cost guide. A single repair, by contrast, is often just a few hundred pounds. That’s exactly why it’s worth having a roofer assess a repair first. They can tell you whether it will actually hold before you commit to one.
Getting the right advice
The honest answer depends on the roof in front of you, not a rule of thumb. A good roofer will tell you plainly if a repair is the sensible option. They won’t push for a full replacement you don’t yet need. If you’re weighing up a bigger project, our new roof cost guide for Twickenham & Richmond covers pitched roofs too.
We also work across Teddington and St Margarets, assessing flat roofs on the same honest basis. We repair where it holds, and replace where it doesn’t.
Related reading
- EPDM Rubber vs GRP Fibreglass vs Felt: The Best Flat Roof Material for London Homes
- How to Tell If Your Roof Needs Replacing: 8 Warning Signs
- What to Do When Your Roof Is Leaking: An Emergency Checklist
- Slate vs Tile Roofing for Period Homes in Richmond upon Thames
- Fascias, Soffits & Guttering: A Homeowner’s Guide to Your Roofline
- Chimney Repairs, Re-Pointing and Removal Explained
- Velux & Roof Windows: Costs, Planning and Installation
- Storm Damage to Your Roof: What to Do and How Insurance Works