GRP fibreglass suits domestic extensions and garages up to 40m2 with a seamless rigid finish lasting 25-40 years. EPDM rubber suits larger or complex flat roofs and installs in colder conditions, lasting 40+ years. GRP needs temperatures above 5C to cure; EPDM has a wider installation window.
If you're replacing a flat roof on an extension, garage or outbuilding, you'll encounter two main modern system options: GRP fibreglass and EPDM rubber. Both are substantially better than the traditional felt systems that dominate on 1980s–2000s properties across Kent. Both carry long material lifespans. But they suit different situations, and the right choice for your roof depends on size, shape, access and budget.
This is an honest comparison, not a sales pitch for one system over the other. We install both regularly across Ashford, Folkestone, Canterbury and the rest of our coverage area, and we recommend based on what fits the roof in front of us.
GRP (Glass Reinforced Plastic) flat roofing is applied as a liquid resin system that cures to a rigid, seamless surface. The installer lays fibreglass matting onto the prepared decking, applies polyester resin and allows it to cure, then applies a topcoat. The result is a one-piece waterproof surface with no joints or seams — the primary failure point of felt systems. GRP has been used in construction for over 30 years and has a well-documented performance record in the UK climate.
EPDM (Ethylene Propylene Diene Monomer) is a synthetic rubber membrane available in large sheets that are bonded to the roof deck using adhesive. The membrane is highly flexible, handles thermal expansion and contraction well, and is available in sheet sizes large enough to cover many domestic flat roofs in a single piece — eliminating the joins that cause most flat roof failures. EPDM has been the dominant flat roofing material in North America for decades and has a strong track record in comparable climates.
A flat roof requires a minimum drainage fall of 1:80 (approximately 12mm per metre) to prevent ponding, the primary cause of premature flat roof failure.
Source: BS 6229 — Code of practice for flat roofs
| Factor | GRP Fibreglass | EPDM Rubber |
|---|---|---|
| Material lifespan | 25–30+ years | 20–25+ years |
| Surface finish | Hard, rigid, smooth | Soft, flexible, matte |
| Seams / joints | None (seamless laminate) | Minimal (large sheet sizes) |
| Complex shapes | More difficult | Easier — membrane conforms |
| Walkability | Good — rigid surface | Limited — rubber can puncture |
| Repair if damaged | Patch with resin — slightly more complex | EPDM tape patch — straightforward |
| Cost (typical domestic) | Slightly higher | Slightly lower |
| UV resistance | Excellent with topcoat | Excellent — inherent to material |
Replacing a flat roof in Kent? Free survey and system recommendation.
Book Free SurveyFor most domestic extensions and garages in Kent, GRP is our default recommendation. The reasons are practical:
GRP is less suitable for roofs with very complex geometry — multiple upstands, acute internal corners, very large areas. On a standard rectangular domestic extension roof it is straightforward to install correctly.
EPDM becomes our preference in three situations:
We don't install new felt flat roofing systems. Felt has a typical service life of 10–15 years, and on many Kent extension roofs from the 1980s–2000s we replace felt systems that are leaking at 12–15 years old. The cost difference between felt and a modern GRP or EPDM system is not large enough to justify a product that will need replacing again within a similar timeframe. If you're investing in a flat roof replacement, do it once properly.
Garage flat roof replacement (GRP, up to 20m²): £800–£1,800
Small domestic extension (up to 15m², GRP): £1,200–£2,200
Medium extension (15–30m², GRP or EPDM): £2,000–£3,500
Large flat roof (30m²+, EPDM): £3,000–£6,500
All prices include removal of existing covering, additional boarding where required, new system installation and a 10-year workmanship guarantee. Free surveys across Ashford, Folkestone, Canterbury and all Kent coverage areas.
Not sure which system is right for your flat roof? We'll survey and recommend the right solution.
Book Free Flat Roof SurveyEvery grp vs epdm flat roofing job starts with a free inspection and written quote before any work begins. We do not start work until you have confirmed the written quote. Our standard rates apply across Ashford and the surrounding Kent area.
We cover all Ashford postcodes and the surrounding towns: Folkestone, Canterbury, Maidstone, Tenterden, Hythe and the villages across the Weald. Emergency cover is available 24 hours a day on 01233 877 146.
No call-out fee across our full service area. Written quote before work starts. For grp vs epdm flat roofing work the quote is provided on the same visit as the inspection in most cases. You pay only for work carried out.
All re-roofing work and major repairs carry our written 10-year workmanship guarantee. Lead flashing work is guaranteed for 10 years. Minor tile repairs carry a 2-year guarantee. The guarantee is provided in writing at completion and transfers to a new owner if the property is sold.
We are registered with the National Federation of Roofing Contractors. Verify our registration at nfrc.co.uk. We carry 5m public liability insurance on every grp vs epdm flat roofing job. Insurance certificate available on request before work starts.
Ashford's housing stock spans five decades of construction: Victorian and Edwardian terraces in Newtown and the older town streets, 1930s semis in Kennington and Willesborough, post-war and 1960s estates at Bockhanger, Stanhope and Park Farm, and more recent development across the southern suburbs.
Each era presents different characteristics. Victorian clay tile on period properties requires matching reclaimed material and lime mortar at any repointing work. 1960s concrete interlocking tile on the estates is now 50-65 years old with corroded nail fixings on most unmodified properties. Understanding which housing era a property belongs to is the starting point for any assessment.
These estates are Ashford's highest-volume source of roofing work. The 1960s-70s concrete interlocking tile stock is now 50-65 years old. Nail sickness is present on the majority of unmodified properties. If you live in one of these areas and have not had roofing work in the last 15 years, a free assessment is worthwhile.
The Victorian terraces in Ashford's Newtown area and the older streets around the town centre require period-appropriate specification: reclaimed or reproduction clay tile, lime mortar at chimney repointing, and conservation-aware approach to any work on visible elevations.
Free survey and advice across Ashford and Kent. Call 01233 877 146.
Call 01233 877 146For context on how roofing costs compare across the range of work we carry out, here are realistic price ranges for the most common jobs across the Ashford area. All prices include labour and materials. VAT is not applicable on most domestic residential roofing work.
| Job Type | Typical Cost |
|---|---|
| Single tile replacement | £150 – £300 |
| Ridge repointing (per 4m) | £200 – £400 |
| Lead chimney flashing replacement | £500 – £1,100 |
| Full re-roof (3-bed semi, concrete tile) | £4,800 – £7,500 |
| Flat roof replacement (GRP, up to 20m2) | £900 – £1,800 |
| Full gutter clear (semi-detached) | £80 – £160 |
| Fascia and soffit replacement (semi) | £800 – £1,800 |
| Roof condition survey | £120 – £200 |
Free written quotes on all work. No call-out fee. Call 01233 877 146 to book.
We are a family-run roofing business based in Ashford, covering the town and the surrounding Kent area. We have been working on roofs in this area since 2003. Every job is carried out by our own employed team — we do not subcontract labour. The people who quote are the people who work.
We are registered with the National Federation of Roofing Contractors (NFRC). Our registration can be verified at nfrc.co.uk. We carry £5m public liability insurance on every job. Our insurance certificate is available on request before any work starts. All re-roofing work carries a written 10-year workmanship guarantee. Lead flashing work is guaranteed for 10 years. The guarantee is transferable to a new owner if the property is sold.
We cover Ashford and a broad area of the surrounding Kent countryside: Folkestone, Hythe, Canterbury, Maidstone, Tenterden, and the villages across the Weald and Romney Marsh. Emergency cover is available 24 hours a day, 7 days a week. Call 01233 877 146 for any roofing emergency. For non-urgent work, we aim to survey within 5-7 working days and have the quote in writing within 48 hours of the survey.
We do not charge for call-outs or surveys. Every job gets a written quote before a single tile is moved. The quoted price is the price on the invoice unless we identify and agree additional scope with you during the work. For re-roofing projects where deck condition is unknown before stripping, we include a clear provisional allowance for batten replacement rather than presenting you with a surprise on invoice.
Last reviewed: July 2026
GRP fibreglass suits domestic extensions and garages up to 40m2 with a rigid seamless finish. EPDM rubber suits larger or complex roofs and installs in colder conditions.
GRP lasts 25-40 years and EPDM 40+ years when correctly installed with adequate drainage fall. Traditional felt lasts only 10-15 years.
EPDM installs in most winter conditions. GRP requires temperatures above 5-10C for the resin to cure, so GRP work is deferred during cold snaps.
Inadequate drainage fall causing ponding is the primary cause. A flat roof needs a minimum fall of 1:80 under BS 6229 to drain correctly and avoid standing water.