Winchester’s damp Itchen Valley winters are hard on traditional felt flat roofs. The combination of persistent moisture, freeze-thaw cycling on exposed membranes and the biological growth encouraged by the valley’s humid microclimate means felt flat roofs on extensions and garages typically last only 10–12 years in this area before failing.
GRP fibreglass is the material we recommend for most Winchester properties. It is a fully seamless installation with no laps or joints to fail, handles standing water well, and when properly installed will outlast the building it is fitted to. It is particularly well-suited to rear kitchen and dining extensions, which account for the majority of our flat roof work across Weeke, Stanmore and Badger Farm.
GRP Fibreglass Flat Roofing Winchester
GRP is laid in a single seamless skin reinforced with fibreglass matting. We install a minimum 40mm polyisocyanurate insulation board underneath to bring the roof to current Building Regulations standards. The topcoat is UV-stabilised and comes in a range of finishes. Installation time for a standard kitchen extension is typically one day, with the surface walkable within 24 hours.
EPDM Rubber Flat Roofing Winchester
EPDM rubber is a cost-effective alternative for larger, simpler areas such as garage roofs. It is a single-ply membrane bonded to the roof deck, and a properly installed EPDM roof will last 25 years with minimal maintenance. We use fully-bonded EPDM, not mechanically fastened, to ensure wind resistance on exposed properties.
Flat roof failing? We survey and quote free of charge. Most extensions and garages in Winchester can be quoted on the same day as the survey. Call 01962 809171.
Flat Roof Prices in Winchester
Small extension (up to 15m²): £800–£1,800 GRP. Standard extension (15–30m²): £1,800–£3,500 GRP. Single garage in EPDM: £1,200–£2,500. Double garage in GRP: £2,500–£5,000. All prices include existing felt removal, insulation board and disposal.
Flat Roof Costs in Winchester (2025)
| Flat Roof Type | Typical Cost |
|---|---|
| GRP fibreglass — extension (20m²) | £1,800–£2,800 |
| GRP fibreglass — garage | £900–£1,600 |
| EPDM rubber — large extension | £1,600–£3,200 |
| Deck replacement (if required) | £150–£450 add |
| GRP manufacturer warranty | 25 years |
What a Flat Roof Survey Involves
We survey the existing membrane from the roof surface — checking for blistering, cracking, joint failure and drainage falls. We inspect the deck boards at the edges and any accessible areas for softness or delamination. We check the outlet drainage and confirm the fall direction. The written survey report confirms whether repair is appropriate or whether replacement is the better value decision, with costings for both options where repair is viable. Deck replacement cost, where required, is confirmed before work starts — not discovered and charged afterwards. Free survey and written fixed quote. Call 01962 809171.