GRP vs EPDM Flat Roofs. Which to Choose.
GRP and EPDM are two modern flat roof systems. Suitability and expected service life depend on the deck, drainage, detailing, installation and product specification. Here is how they compare.
Key takeaways
- GRP is harder, walk on, takes a coloured topcoat, fibreglass.
- EPDM is a single rubber sheet, flexible in cold, mostly seamless.
- GRP usually costs a little more per square metre than EPDM, though the gap is small.
- Product warranties vary by manufacturer, system and installer. Check the written terms before choosing.
- GRP is better for high traffic and complex shapes. EPDM for large simple shapes.
GRP fibreglass
Glass reinforced polyester laid wet on an OSB deck and finished with a coloured topcoat (slate grey, anthracite, dark grey). Hard, walk on, looks tidy. Best for porches, dormers, garages, and any flat roof you will ever step on.
EPDM rubber
Single piece rubber membrane bonded to the deck. No seams on most domestic roofs. Flexible in cold, will not crack, very forgiving on slight movement. Black only. Best for large simple flat roofs.
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How the two compare on cost
GRP normally sits a little above EPDM per square metre, but on a normal domestic roof that gap is small next to the deck work and the detailing. Both are priced on measured area, the number of upstands and outlets, and how much of the existing deck has to be renewed first. Worth choosing on suitability rather than price. The figure comes in writing after the roof has been looked at.
Which to choose
GRP for porches, garages, dormers, anything walkable. EPDM for big simple extension roofs where seamless is the priority. Either way, neither is the leaky felt of the 1970s, both will give you 20 plus years if installed properly.
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About the author
David Boardman founded Boardman Roofing in 2018. Dave has 25 years on the tools. Read 150+ Google reviews or call 07879 736629.
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150+ Google reviews. Dave has 25 years on the tools.
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