Ask three roofing contractors to quote for the same flat roof and you will often get three different materials recommended — not because two of them are wrong, but because most flat roofers specialise in installing one system and naturally present it as the best option. EPDM installers favour EPDM. GRP installers favour GRP. Very few homeowners get an unbiased side-by-side comparison before they commit several thousand pounds to a covering that needs to perform for the next two to five decades.
The three coverings that dominate the UK domestic flat roof market today are EPDM rubber membrane, GRP fibreglass (also called glass reinforced plastic), and felt — either traditional built-up felt or modern high-performance torch-on felt. Each has a genuinely different set of strengths, and the right choice depends on your roof's shape, your budget, and how long you want the covering to last before you think about it again.
This guide compares all three on the metrics that actually matter: installed cost, realistic lifespan, how they handle complex roof shapes, maintenance requirements, and the specific failure modes to watch for with each. It ends with a straight decision framework based on the type of roof you have.
The three materials side by side
Before the detail on each material, here is the full comparison in one place. Costs assume a standard domestic installation with normal access — complex roofs, poor access, or the need for scaffolding will push all three figures upward proportionally.
| Factor | EPDM Rubber | GRP Fibreglass | Felt (Torch-On) |
|---|---|---|---|
| Realistic lifespan | 30–50 years | 25–40 years | 15–25 years |
| Installed cost per m² | £70–£100 | £80–£120 | £50–£80 |
| Seams / joints | Single sheet, minimal seams | Fully seamless, moulded | Multiple overlapping layers |
| Handles complex shapes | Good with detailing skill | Excellent — moulds to any shape | Difficult around upstands |
| Walkability | Moderate — avoid sharp objects | Excellent, impact-resistant | Poor — punctures easily |
| UV / weather resistance | Excellent | Excellent | Degrades faster in direct sun |
| Repairability | Simple patch repairs | Requires resin/gel coat matching | Simple patch repairs |
| Typical warranty offered | 20–25 years | 15–25 years | 10–15 years |
Overall performance scoring (out of 10)
What each material costs on a typical UK extension roof
These figures are for a standard 15m² single-storey extension roof — the most common domestic flat roof job — with reasonable ground-level access and no scaffolding required.
EPDM rubber membrane
EPDM (Ethylene Propylene Diene Monomer)
Single-ply synthetic rubber sheet, typically installed in one continuous piece with mechanically fixed or fully adhered edges.
EPDM is supplied in large rolls — often wide enough to cover an entire domestic roof in a single sheet with no field seams at all, which removes the single biggest cause of flat roof failure: seam breakdown. Where seams are unavoidable on larger roofs, they are joined with a specialist tape or liquid-applied seam adhesive that, correctly installed, is as durable as the membrane itself.
The material is highly flexible, which lets it accommodate a building's natural thermal movement and minor structural settlement without cracking — something rigid materials like GRP cannot do as well. This flexibility is a major reason EPDM roofs regularly reach 30 to 50 years of service life.
- Excellent UV, ozone, and weather resistance — does not become brittle with age like older felt
- Minimal or zero seams on most domestic roof sizes
- Easy to repair — small punctures are patched with the same membrane and adhesive
- Works well on roofs with moderate movement (timber decks, extensions on older properties)
- The roof is a simple rectangular or near-rectangular shape
- You want the longest realistic lifespan for the budget
- The roof deck is timber and likely to move slightly over time
- You want a covering that's simple and cheap to repair later
- The roof has many upstands, roof lights, or complex detailing
- You need a hard-wearing, frequently walked-on terrace surface
- Your installer is not EPDM-trained — poor detailing at edges is the main cause of early failure
GRP fibreglass
GRP (Glass Reinforced Plastic / Fibreglass)
Liquid resin laminated over glass fibre matting on site, cured into a single rigid, fully bonded, seamless surface.
Unlike EPDM and felt, GRP is not a pre-made sheet — it is built up in layers on the roof itself, which means it moulds perfectly around upstands, roof lights, pipe penetrations, and awkward angles with genuinely no joints anywhere on the finished surface. This makes it the preferred choice for roofs with more complicated geometry, such as dormer roofs, bay window roofs, or roofs with multiple abutments.
Once cured, GRP is rigid, hard-wearing, and highly resistant to impact and foot traffic, which is why it's commonly specified for roof terraces, balconies, and walkways as well as standard flat roofs. Its rigidity is also its main limitation — it does not flex with structural movement the way EPDM does, so deck stability matters more with GRP than with rubber.
- Completely seamless — the single biggest advantage over both other materials
- Excellent for roofs with roof lights, upstands, or unusual shapes
- Fully walkable and impact-resistant once cured — suited to terraces and balconies
- Wide colour range for the top gel coat, useful where the roof is visible
- The roof has multiple upstands, roof lights, or an irregular shape
- The area will see regular foot traffic (terrace, balcony, walkway)
- The roof deck is structurally solid plywood/OSB with minimal expected movement
- You want a visibly clean, seamless finish
- The deck is older timber with any doubt about ongoing movement
- You need the cheapest possible option for a simple rectangular roof
- Future repairs need to be invisible — colour and sheen matching gel coat is skilled work
Felt roofing (torch-on and built-up)
Felt (High-Performance Torch-On / Built-Up)
Bitumen-based felt applied in two or three overlapping layers, heat-welded (torch-on) or bonded with hot bitumen (built-up), with a mineral or reflective cap sheet on top.
Modern high-performance torch-on felt is a significant improvement over the older two-layer "shed felt" systems that gave the material its poor reputation. A correctly specified three-layer system — underlay, intermediate layer, and a mineral-finished cap sheet — from a reputable manufacturer such as IKO or Ruberoid, installed by a trained contractor, can reasonably be expected to last 15 to 25 years.
The trade-off is the multiple overlapping seams inherent to the system, each of which is a potential failure point if not correctly heat-welded, and a lower tolerance for UV exposure and foot traffic than EPDM or GRP. Felt remains the lowest-cost option and is a reasonable choice for garages, sheds, and outbuildings where the roof's lifespan expectation is inherently shorter than a habitable extension.
- Lowest upfront installed cost of the three materials
- Fast to install — a standard job is often completed in a day
- Widely available — most general roofers can install felt without specialist training
- Reasonable choice for lower-value structures (sheds, garages, outbuildings)
Which material suits your roof?
Use these factors together rather than any single one in isolation — the right material is usually the one that satisfies your two or three highest priorities, not necessarily the cheapest or the longest-lasting on paper.
Roof shape and complexity
Simple rectangle → EPDM or felt. Multiple upstands, roof lights, or dormers → GRP's seamless moulded finish handles detailing far more reliably.
Budget vs lifespan
Lowest upfront cost → felt, accepting a shorter lifespan. Best cost-per-year-of-service → EPDM, in most standard cases.
Foot traffic
Terrace, balcony, or roof accessed regularly → GRP's impact resistance is the clear winner. Occasional maintenance access only → EPDM is fine.
Deck condition and age
Older timber deck with any flex or movement → EPDM's flexibility tolerates this better than rigid GRP, which can crack over an unstable substrate.
Before you sign off on a quote
- ✅ Confirm the exact specification — layer count for felt, membrane thickness for EPDM (1.2mm or 1.5mm), or resin/matting weight for GRP
- ✅ Ask what warranty is offered in writing, and whether it covers materials only or materials and labour
- ✅ Check the installer holds manufacturer accreditation for the specific system quoted — this is what makes many warranties valid
- ✅ Confirm insulation is being upgraded to current Building Regulations U-value requirements if this is a full re-cover, not just a like-for-like patch
- ✅ Ask how the roof's fall (slope to drainage) will be achieved — firrings, tapered insulation, or the existing deck — poor drainage design shortens the life of any material
Drainage design affects every material equally — a perfectly installed EPDM, GRP, or felt roof will still fail early if water is allowed to pond. See our full guide to flat roof drainage problems and solutions for what correct fall and outlet placement should look like.
Frequently asked questions
Which flat roof covering lasts the longest?
EPDM rubber membrane typically lasts the longest of the three main UK flat roof coverings, with a realistic lifespan of 30 to 50 years when correctly installed with welded or taped seams. GRP fibreglass is close behind at 25 to 40 years, since it forms a single seamless surface with no joints to fail. Felt roofing, even modern high-performance torch-on felt, lasts 15 to 25 years, with older two-layer shed-style felt lasting closer to 10 years.
Is GRP fibreglass better than EPDM rubber?
Neither is universally better — they suit different roofs. GRP forms a single rigid, seamless surface that handles complex shapes, upstands, and roof lights very well, and it's walkable and impact-resistant once cured. EPDM is a flexible rubber sheet that accommodates building movement better than rigid GRP, has a longer typical lifespan, and is usually slightly cheaper on straightforward rectangular roofs. For a simple extension roof, EPDM is often the more cost-effective choice. For a roof with multiple upstands or angles, GRP's seamless finish is often preferred.
How much does a new flat roof cost in the UK in 2026?
For a typical UK domestic flat roof, felt (three-layer torch-on) costs approximately £50 to £80 per square metre installed, EPDM rubber costs approximately £70 to £100 per square metre installed, and GRP fibreglass costs approximately £80 to £120 per square metre installed. A standard 15 square metre extension roof therefore costs roughly £750–£1,200 in felt, £1,050–£1,500 in EPDM, or £1,200–£1,800 in GRP, including labour, materials, and edge trims. Scaffolding, if needed, is an additional cost.
Can you walk on a GRP fibreglass roof?
Yes, cured GRP fibreglass roofing is fully walkable and one of the more impact-resistant flat roof coverings available, which is why it's often specified for roof terraces and balconies with light foot traffic. EPDM can tolerate occasional foot traffic for maintenance access but is more easily damaged by sharp objects than GRP. Felt is the least tolerant of regular foot traffic and can be punctured or blistered by repeated walking, especially in warm weather.
Do flat roof coverings need planning permission in the UK?
Re-covering an existing flat roof with EPDM, GRP, or felt is generally considered like-for-like maintenance and does not require planning permission or Building Regulations approval on its own, provided you are not raising the roof height, altering its pitch, or extending its footprint. However, if the work is part of a new extension or loft conversion, Building Regulations approval is required regardless of which covering is used, and planning permission may also apply. Always confirm with your local authority or installer if the project involves anything beyond a straightforward re-cover.
Get the right material recommended for your actual roof
The best flat roof covering is the one suited to your roof's shape, deck, and how it's used — not whichever system the nearest contractor happens to install. Find a vetted local specialist who works with all three materials and can recommend based on your roof, not their van signage.
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