New GRP flat roof installation
We install GRP fibreglass systems to manufacturer specifications on garages, extensions, porches and commercial properties. Full strip of the existing covering and deck check included before installation.
GRP Fibreglass Roofing Hampshire
CMW Roofing & Renovations installs and repairs GRP fibreglass flat roofs throughout Hampshire. GRP (Glass Reinforced Plastic) is our preferred flat roofing system — it outperforms traditional felt on durability, lifespan and weather resistance, and typically carries a 20-year manufacturer guarantee.
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What we offer
GRP fibreglass roofing is a single-ply, seamless flat roof system applied as a liquid that cures to form a tough, waterproof surface. Unlike traditional felt systems, which rely on lapped joints that can lift and crack over time, a GRP roof has no seams — the entire surface is one continuous material, eliminating the most common failure point of conventional flat roofing. We install GRP systems on garages, extensions, porches, bay windows and commercial flat roofs across Hampshire.
GRP is often the right answer when a traditional felt flat roof has failed and you want a long-term replacement. We also carry out flat roof repairs where the existing system can be salvaged, and full pitched roof replacements where the roof structure itself needs addressing.
Felt to GRP conversion
Replacing a failed or ageing felt flat roof with a GRP system is one of our most common jobs. We strip the existing felt, check and replace any damaged decking, and install a new GRP surface with upstands and flashings.
GRP repairs and patch work
If an existing GRP system has a localised crack, blister or failed upstand, we carry out GRP-compatible repairs using the same laminate system. A properly carried out GRP repair is seamless and can extend the life of the roof considerably.
GRP bay window roofs
Bay window roofs are particularly prone to leaking at the junction with the wall. We install GRP systems on bay roofs with properly formed upstands and lead soakers or code 4 lead at the wall junction.
GRP for extensions and outbuildings
Rear extension flat roofs and outbuilding roofs are ideal applications for GRP. We install to the same standards as main roof work, with written guarantees on both materials and workmanship.
Flat roof surveys and reports
If you're unsure of the condition of an existing flat roof — before buying a property, for example, or after a leak — we carry out a written condition report covering the surface, drainage, upstands and any visible defects.
Frequently asked questions
How long does a GRP flat roof last?
A properly installed GRP roof will typically last 25–30 years or more. Most GRP systems carry a 20-year manufacturer guarantee on the materials. Our workmanship is guaranteed separately. In contrast, a standard felt flat roof typically lasts 10–15 years before requiring significant attention.
Is GRP better than EPDM rubber roofing?
Both systems are significantly better than traditional felt. GRP is harder and more rigid, while EPDM is more flexible. GRP tends to perform better in areas with foot traffic and at junctions with upstands, because it can be formed continuously without seams. EPDM is more elastic and can accommodate minor structural movement. We install GRP as our preferred system.
How much does a GRP flat roof cost in Hampshire?
Pricing varies depending on roof size, access, and the condition of the existing deck. We provide a free written quote before starting.
Can GRP be installed in cold or wet weather?
GRP requires dry conditions and a minimum temperature of around 5°C to cure correctly. We do not install GRP in rain or frost. If weather intervenes after stripping has started, we will make the roof temporarily weatherproof while waiting for suitable conditions.
Does a GRP roof need maintenance?
Very little. We recommend a light clean every couple of years to prevent moss and algae build-up, and a visual check of the upstands and any penetrations. Other than that, a well-installed GRP system should require no intervention for many years.
Get a free GRP roofing quote
Call or message for a free, no-obligation quote on a GRP flat roof for your garage, extension or bay window. We cover Southampton, Portsmouth, Fareham, Winchester and across Hampshire.