GRP fibreglass flat roofs in Amersham — tough, seamless, walkable.
GRP (glass-reinforced polyester) is the premium flat roof option. It’s applied as a liquid resin over fibreglass matting and cures into a hard, completely seamless surface. No joins, no seams, no weak points. It’s the right choice for balconies, roof terraces, and any flat roof you need to walk on regularly.
We install, repair and replace GRP flat roofs across Amersham and the surrounding area.
Call 01494 702 599 for a free survey.
How GRP works
Unlike felt or EPDM (which are sheets laid on top of the roof), GRP is built up on site in layers:
- The roof deck is prepared (usually 18mm OSB or plywood)
- A layer of GRP resin is applied
- Fibreglass matting (chopped strand mat) is laid into the wet resin
- A second layer of resin is applied over the top
- The whole thing cures into a single, rigid, waterproof shell
- A topcoat is applied for UV protection and colour
The result is a completely seamless surface with no joins anywhere — the whole roof is one continuous waterproof layer. That’s the main advantage of GRP over other systems.
We use Cromar GRP systems — a UK manufacturer with a strong track record in the domestic market.
GRP repairs
GRP roofs are tough, but they’re not indestructible. The problems we see most:
- Surface crazing — fine cracks in the topcoat, usually cosmetic. A new topcoat layer fixes this.
- Impact damage — something dropped on the roof, or heavy foot traffic in one area, has cracked the laminate. We cut out the damaged area and re-laminate a patch.
- Edge debonding — the GRP has lifted away from the edge trims or upstands. We grind back, re-laminate and re-seal.
- Osmotic blistering — moisture trapped under the laminate causing bubbles. Each blister gets ground out and re-laminated.
Typical GRP repair cost: £200–£600 depending on the extent.
GRP installation and replacement
If you’re replacing an old flat roof and want the longest-lasting, most durable option, GRP is it.
What you get:
- Old covering stripped and removed
- Deck inspected and replaced where needed
- New 18mm OSB3 or plywood deck laid (GRP needs a rigid, stable base)
- Insulation added if required
- Full GRP laminate system applied — resin, matting, resin, topcoat
- New edge trims, drip details and flashings
- Choice of topcoat colour (grey is standard, other colours available)
- All waste removed
Typical prices:
| Roof type | Typical price |
|---|---|
| Porch | £1,000–£1,500 |
| Single garage | £1,500–£2,500 |
| Double garage | £2,500–£4,000 |
| Small extension | £2,000–£3,500 |
| Large extension | £3,500–£5,500 |
| Balcony or roof terrace | £3,000–£6,000 |
GRP costs more than EPDM or felt upfront, but lasts 25–30 years with minimal maintenance and gives you a walkable surface.
When GRP is the right choice
- You need to walk on the roof regularly (balcony, terrace, roof garden access)
- You want a clean, finished-looking surface
- You’re doing a premium extension and want the roof to match the quality of the build
- You want minimal maintenance over the longest possible lifespan
- The roof is complex with lots of upstands, penetrations and detail work (GRP handles complex shapes well because it’s moulded on site)
When something else might be better
- Budget is tight — EPDM gives you 90% of the performance at 60% of the cost
- The roof is very large — GRP works best on roofs under about 40m²
- You need to install in cold or wet weather — GRP needs temperatures above 10°C and dry conditions to cure properly
Common questions
How long does GRP last?
25–30 years is typical. With a topcoat refresh every 10–15 years, some GRP roofs last significantly longer.
Can GRP go over my existing felt roof?
No. GRP needs a rigid, stable deck (OSB3 or plywood). The old covering has to come off and the deck has to be right before GRP goes on.
Is GRP slippery when wet?
The standard topcoat can be slippery. If the roof is a walkway or terrace, we add a non-slip aggregate to the topcoat at no extra cost.
Can GRP crack?
On a properly prepared deck, cracking is rare. Most GRP failures happen when the deck wasn’t rigid enough or the resin was applied in poor conditions. We’re careful about both.
What colours are available?
Grey is standard. Dark grey, green, black, and other colours are available on request.
Where we cover
We install and repair GRP flat roofs across Amersham, Old Amersham, Little Chalfont, Chalfont St Giles, Chalfont St Peter, Great Missenden, Chesham, Beaconsfield, Penn, Holmer Green, and Hazlemere.
Get a free quote
Call us or send a message. We’ll survey the roof and give you a fixed-price quote.
Phone: 01494 702 599
Email: info@amershamroofers.co.uk