Felt vs EPDM vs GRP: choosing a flat roof system
There is no single best flat roof system — there is a best system for a particular deck, shape and use. Here is how the three common options actually differ.
GRP Fibreglass Roof
GRP (fibreglass) gives a seamless, glass-hard finish that reads cleanly against period brick — our usual call for visible bay roofs and small flat areas.
Lifespan
25–30 years when laid in the right weather window with proper resin ratios.
Cost / m²
£100–£150 supplied and laid
Category
flat
Best for
Bay-window roofs, small porches, dormer cheeks — anywhere the finish is visible and a seam would show.
Where it fails
- Hairline crazing if laid too thick or in cold conditions
- Edge trims pulling away when fixings are skimped
- Difficult to repair invisibly once weathered
- Wrong-gauge tissue or cheap resin shows up in 5 years
Our repair approach
We lay GRP at 450g chopped strand mat with proper trim returns, and avoid pouring resin in sub-10°C weather — most failures we patch trace back to that.
GRP fibreglass by area
Our guides on this
Flat roof cost: GRP versus EPDM versus felt
Torch on felt is cheapest to install and shortest lived. EPDM rubber suits larger, simple areas in one seamless sheet. GRP costs most and looks the sharpest on visible bays and porches, but it is weather dependent to lay and unforgiving of movement.
Single-ply vs mastic asphalt: which flat roof suits your property
Single-ply membranes suit most domestic and light commercial flat roofs — lighter, faster and typically £130–£170 per square metre. Mastic asphalt is heavier, costlier and slower, but it is unbeatable on balconies, terraces and roofs that take foot traffic or need a seamless finish over complex detail.