When repair stops making sense, we do full flat roof replacements across Amersham.
If your flat roof is past 20 years old, leaking in multiple places, or the substrate underneath has gone soft, replacement is usually the smarter long-term option. We strip the old covering, check the timber, and install a new system that will last 25–40 years depending on the material.
Call 01494 702 599 for a free survey and quote.
When does a flat roof need replacing?
Not every leak means a new roof. But here are the signs that replacement makes more sense than another repair:
- Multiple leaks in different areas — the membrane has failed generally, not just in one spot
- Ponding water that won’t drain — the fall is wrong and can’t be fixed by patching
- Soft or spongy deck — the timber underneath has absorbed water and lost its strength
- Felt that’s cracked and granule-bare across the whole surface — beyond economic repair
- You’ve already had two or three repairs in the last few years — the roof is telling you something
If you’re not sure, we’ll come out, have a look, and tell you honestly whether a repair will buy you more time or whether replacement is the right call.
Your options for a new flat roof
We install three main systems. Each has different strengths, lifespans, and price points.
EPDM rubber roofing
A single sheet of synthetic rubber bonded to the deck with adhesive. No joins on most domestic roofs, which means no seams to fail. The go-to choice for most garage and extension flat roofs in Amersham.
- Lifespan: 30–40 years
- Pros: seamless, flexible, handles thermal movement, UV-resistant
- Cons: harder to repair if damaged, relies on good adhesion
- We use: Firestone RubberCover — industry standard with a 20-year manufacturer guarantee
GRP fibreglass roofing
A liquid-applied system that cures into a hard, seamless, walkable surface. Popular for balconies, roof terraces, and flat roofs you need to walk on regularly.
- Lifespan: 25–30 years
- Pros: completely seamless, very durable, walkable, clean finish
- Cons: rigid (can crack on poorly prepared decks), needs warm dry conditions to install
- We use: Cromar GRP systems
Three-layer felt roofing
The traditional option, modernised. Three layers of high-performance torch-applied felt. Still a solid choice, especially for budget-conscious replacements.
- Lifespan: 15–20 years
- Pros: proven system, lower cost, widely repairable
- Cons: shorter lifespan than EPDM or GRP, seams are a potential weak point
- We use: IKO and Permaroof torch-on felts
We’ll recommend the right system for your roof based on the size, use, budget, and how long you want it to last. No pressure toward the most expensive option.
What the work involves
A typical flat roof replacement takes 2–3 days for a standard garage or extension. Here’s the sequence:
- Strip the old covering — remove the existing membrane, insulation if needed, and any rotten timber
- Inspect and repair the deck — replace any damaged boards or joists
- Install insulation (if upgrading) — improves energy efficiency and meets current Building Regs for habitable rooms
- Lay the new membrane — EPDM, GRP, or felt depending on what you’ve chosen
- Flash and trim — new flashings where the roof meets walls, new drip edges, new trims
- Clean up — all waste removed, site left tidy
What it costs
Typical prices for flat roof replacement in the Amersham area:
| Type of work | Typical price |
|---|---|
| Garage flat roof replacement (single) | £1,200–£2,200 |
| Garage flat roof replacement (double) | £2,000–£3,500 |
| Extension flat roof replacement (small) | £1,800–£3,000 |
| Extension flat roof replacement (large) | £3,000–£5,000 |
| Dormer flat roof replacement | £1,500–£3,000 |
| Porch flat roof replacement | £800–£1,500 |
Prices depend on material choice, deck condition, access, and whether insulation is being added. We quote a fixed price after a free survey — no estimates that grow later.
Common questions
How long does a flat roof replacement take?
Two to three days for a standard garage or extension. Larger roofs or roofs needing significant deck repairs may take longer — we’ll agree the schedule with you before starting.
Will I need Building Regulations approval?
If the roof covers a habitable room (kitchen extension, bedroom, living room) and you’re replacing more than 50% of it, Building Regs require you to upgrade the insulation to current standards. We handle this as part of the job. Garage roofs don’t usually require Building Regs sign-off.
Can you do it in winter?
EPDM can be installed in most conditions above 5°C. GRP needs warmer, dry weather (ideally above 10°C). Felt is the most weather-tolerant of the three. We’ll advise on timing based on what you choose.
What guarantee do I get?
All our work comes with a workmanship guarantee. The materials carry their own manufacturer guarantees — typically 20 years for Firestone EPDM and 25 years for GRP systems.
Where we cover
We do flat roof replacements across Amersham, Old Amersham, Little Chalfont, Chalfont St Giles, Chalfont St Peter, Great Missenden, Chesham, Beaconsfield, Penn, Holmer Green, and Hazlemere.
Get a free survey
Call us or send a message. We’ll come out, inspect the roof, and give you a fixed-price quote with our honest recommendation.
Phone: 01494 702 599
Email: info@amershamroofers.co.uk