EPDM vs GRP vs felt: which flat roof is best?

All three systems can give long service when installed properly. Below we compare them honestly.

How do the three systems compare at a glance?

When is EPDM the best choice?

• Simple rectangular roofs on extensions, dormers and garages
• Where you want a single sheet with few or no joints
• Where flame free installation is preferred, for example near timber cladding
• Roofs with limited foot traffic

When is GRP the best choice?

• Roofs with lots of details, such as roof lights, upstands and outlets
• Balconies and roofs you will walk on, with a suitable finish
• Where you want a smooth, neat finish and coloured trims
• Dormers and porches where appearance matters

GRP needs dry weather to cure properly, so timing is more weather dependent.

When is felt still a good choice?

• Larger roofs where budget matters
• Garages and outbuildings
• Roofs that need to take regular foot traffic for maintenance
• Matching or repairing an existing felt roof

Modern felt systems are a big improvement on old single layer felt, but they are usually torch applied, which needs careful fire safety around timber.

Does insulation change the choice?

All three can be laid on a warm roof build up, with insulation boards above the deck. If you are replacing more than half of a flat roof, Building Regulations usually expect the insulation to be upgraded where practical. That affects the height of the roof and its edges, so we plan it at the survey.

What do we see on local flat roofs?

Across Crawley, East Grinstead and the surrounding towns, many flat roofs on garages and 1960s to 1980s extensions are old felt, often with ponding water from poor falls and blocked outlets caused by leaves from nearby trees. Whichever system you choose, correcting the falls and the drainage is as important as the membrane.

When to call a roofer

How is each system installed?

EPDM comes as a large sheet, often one piece for a garage or small extension. It is bonded to the deck with adhesive, and the edges are finished with trims and, where needed, flashings at the walls. No flame is used.

GRP is built in place. A resin is applied to the deck, a glass fibre mat is laid into it and wetted out with more resin, and once it has cured a coloured topcoat is applied. Preformed trims give the edges a neat finish. It needs dry weather and suitable temperatures to cure properly.

Built up felt is laid in layers, typically a base layer and a cap sheet with a mineral surface. Most modern systems are torch applied, so fire safety around timber, cladding and roof voids is critical. Some systems are cold applied or self adhesive.

Which flat roof material is best for a garage?

Older garage roofs sometimes have asbestos cement sheets. These must be identified and dealt with safely before any new roof is fitted.

Which flat roof material is best for an extension?

For a rear extension, the roof is often seen from upstairs windows and may have roof lights. EPDM and GRP are both popular. GRP handles a busy roof with many details neatly, while EPDM is excellent on simple shapes. A warm roof build up is normally the right choice over a heated room.

Can you walk on EPDM, GRP and felt?

All three tolerate occasional foot traffic for maintenance. For a balcony or a roof used regularly, GRP with a suitable surface, or a paved or decked finish on supports above the membrane, is a better choice. Remember that turning a flat roof into a balcony or terrace usually needs planning permission and must meet Building Regulations for guarding.

What goes wrong with each system?

• EPDM: problems usually come from poor adhesion, badly detailed corners or trims, or damage from sharp objects.
• GRP: problems usually come from laying in damp or cold conditions, a deck that moves, or a laminate that is too thin.
• Felt: problems usually come from old single layer felt, poor laps, and ageing from sun where there is no protective surface.

In every case, the quality of installation matters more than the name of the product.

What do local homeowners usually choose?

On Crawley’s rows of postwar garages, felt and EPDM are common choices because they detail well where garage roofs join. On extensions and dormers in East Grinstead and the surrounding villages, many homeowners choose GRP or EPDM for a clean finish. We are happy to show you samples and explain what would suit your roof. See EPDM rubber roofing and GRP fibreglass roofing.

How do the costs compare?

Felt is usually the most economical, EPDM sits in the middle and GRP is often a little more, but size, shape and details can change that order. We price your roof after a free survey. Read flat roof replacement cost.

Step by step: choosing your flat roof system

1. Measure and sketch the roof, noting roof lights, pipes and walls it meets.
2. Decide how it will be used. Maintenance only, or a balcony or terrace?
3. Check the deck and falls with a roofer, because these affect every option.
4. Decide on insulation, especially over a heated room.
5. Consider appearance from upstairs windows and neighbouring homes.
6. Compare like for like quotes that list the deck work, insulation, trims and drainage.

Does each system need maintenance?

All flat roofs benefit from a yearly check. Clear leaves from outlets and gutters, look for lifted trims, and check sealed joints around roof lights and pipes. EPDM and GRP need very little beyond this. Felt roofs with a mineral surface may shed some granules over time, which is normal, but bare patches should be looked at.

Frequently asked questions

Choose the right flat roof

Read more about EPDM rubber roofing, GRP fibreglass roofing and flat and felt roofing, or see flat roofing in Crawley and flat roofing in East Grinstead. Call 01342 445004, WhatsApp 07939 862 818, or get a free survey.