A GRP fibreglass roof usually costs £70–£110 per m² installed in the UK. That’s the honest answer. But honestly, that range is about as useful as telling someone a car costs “between £5,000 and £80,000,” so let’s get into what actually moves the number up or down.
If you’re replacing a flat roof or costing out a new extension, this guide will help you check whether a quote is fair before you reply. Every figure here reflects current UK contractor pricing for supply and installation as of 2026.
GRP Roof Costs in 2026: Key Figures at a Glance
The main installed cost for a standard GRP fibreglass roof is £70–£110 per m² in 2026. That covers a fully laminated system with topcoat and trims, installed by a qualified roofer. It does not include DIY material kits, which typically cost £25–£40/m² for materials only.
Guarantee length is one of the clearest ways to understand why one GRP quote costs more than another. Longer guarantees usually mean thicker laminate layups, sometimes double-mat systems, better UV-resistant topcoats, and manufacturer-certified materials. A 15-year system might use a single layer of 450g CSM with a standard topcoat. A 40-year system may specify a double-mat layup, premium flowcoat, and full manufacturer sign-off.
| Guarantee Length | Approx. Cost per m² (Installed) |
|---|---|
| 15 years | £75 |
| 20 years | £80 |
| 25 years | £86 |
| 30 years | £94 |
| 40 years | £110 |
To make those per-m² rates more useful, here are estimated total costs for three common roof sizes:
| Roof Type | Approx. Size | Estimated Total (Standard Spec) | Estimated Total (Premium Spec) | Typical Install Time |
|---|---|---|---|---|
| Small garage roof | ~15 m² | £1,125–£1,350 | £1,410–£1,650 | 1–2 days |
| Standard extension roof | ~25 m² | £1,875–£2,250 | £2,350–£2,750 | 2–3 days |
| Large flat roof | ~40 m² | £3,000–£3,600 | £3,760–£4,400 | 3–5 days |
Standard GRP roofing sits in the £70–£90/m² bracket. Premium specifications, including thicker laminates and improved topcoats, tend to cost £90–£120/m². Insulated GRP systems, meaning warm roof build-ups with rigid insulation boards underneath, cost £100–£130/m².
All roofer quotes should include VAT at 20%. Always check. VAT has a reliable habit of materialising at the bottom of a quote after you’ve already mentally spent the saving.
What Affects the Cost of a GRP Roof?
Roof Size
Bigger roofs cost less per square metre because materials can be ordered more efficiently and labour time per m² falls as the job scales. A 10 m² porch roof might come in around £95/m² installed. The same specification on a 40 m² flat roof could sit closer to £75/m².
Roof Complexity
A plain rectangle with no penetrations is the cheapest to install. Add a hip, valley, upstand, or pipe through the middle and the price rises because each detail needs careful lamination and extra trims.
Deck Condition
GRP is laminated directly onto a timber deck, usually 18 mm OSB or plywood. If the existing boarding is damaged, it needs replacing before any laminate goes down. Expect that to add £15–£25 per m².
New Install vs. Overlay
Removing and disposing of old felt or EPDM means skip hire and extra labour. If the existing substrate is sound, a GRP overlay avoids that cost. A strip-and-redeck job for a 15-year spec typically costs around £92/m². New work on a prepared deck sits at about £75/m².
Regional Labour Rates
Roofers typically charge £23–£30 per hour, or £180–£250 per day for GRP installation. London and the South East carry a 15–25% premium, so a £2,000 job in the Midlands could land at £2,400–£2,500 in London.
Materials vs. Labour Split
Materials make up roughly 60–70% of the total installed cost, with labour covering the rest. Moving from a 20-year to a 40-year system adds around £20–£25/m² in materials, but only £5–£10/m² in extra labour.
Insulation
Adding insulation to create a warm roof system costs an extra £20–£40 per m². For habitable rooms underneath, such as a bedroom, home office, or kitchen extension, the thermal improvement is significant and Building Regulations may require it.
Contractor Accreditation
BBA-certified or manufacturer-approved installers, including accreditations from bodies such as the BBA, Polyroof, or Topseal, typically charge 5–15% more than non-accredited roofers. In return, they can offer 10–20 year workmanship guarantees backed by the system manufacturer.
GRP vs. EPDM vs. Torch-On Felt: Cost and Lifespan Compared
Choosing a flat roofing system is really a question of how you want to spend the money: more now, or more later in smaller and more frequent instalments.
| Feature | GRP Fibreglass | EPDM Rubber | Torch-On Felt (3-Layer) |
|---|---|---|---|
| Installed cost per m² | £70–£110 | £60–£95 | £45–£70 |
| Typical lifespan | 25–40 years | 30–50 years | 15–20 years |
| Approx. cost per m² per year of service | £2.80–£3.50 | £1.90–£2.40 | £2.65–£3.90 |
| Maintenance | Very low | Very low | Moderate |
| Seamless finish | Yes, once cured | No, joins possible | No, lapped joints |
| Complex shapes | Excellent | Good | Adequate |
| Repair ease | Simple patch/recoat | Patch kit | Section replacement |
GRP Fibreglass
Once cured, GRP forms one seamless shell. No joints, no laps, no seams waiting to open up on a wet November Tuesday. It carries the highest upfront cost here, but the whole-life cost is often low once you account for the repairs you’re not doing. When something does need attention, it’s typically under £200.
Standard GRP systems (£70–£90/m²) suit most domestic projects. Premium systems (£90–£120/m²) make sense where foot traffic is heavier, the guarantee needs to stretch further, or you simply don’t want to think about the roof again for a very long time.
EPDM Rubber
EPDM offers a 30–50 year lifespan at a slightly lower installed cost than GRP. Maintenance is minimal. The catch is that fewer local installers specialise in it, which can reduce quote options and make warranty-backed work harder to source in some areas.
Torch-On Felt (3-Layer)
Felt remains the cheapest option at £45–£70/m². It’s proven and widely available, but with a 15–20 year expected lifespan, you may replace it again before a GRP roof needs its first major attention. Regular inspections and occasional recoating keep it watertight in the meantime.
For most homeowners replacing a domestic flat roof, GRP offers strong long-term value. But if you’re genuinely planning to sell within five years, felt may make more financial sense because the lower upfront cost is unlikely to be recovered in the sale price during that window.
How Much Do GRP Materials Cost for a DIY Job?
This breakdown is useful whether you’re planning a DIY job or checking whether a roofer’s quote includes enough product for a proper application.
DIY Material Costs for a Typical 20 m² Roof
| Material | Quantity Needed | Approx. Unit Cost | Approx. Total Cost |
|---|---|---|---|
| 450g Chopped Strand Mat (CSM) | 20 m² + extra for overlaps/upstands | ~£2.50/m² | £55–£65 |
| Polyester Resin | 30–40 kg | ~£5.35/kg | £160–£214 |
| Topcoat (Flow Coat) | 10–16 kg | ~£6.00/kg | £60–£96 |
| Catalyst (MEKP) | 1–2% by weight of resin/topcoat | Included with resin/topcoat | — |
| Total DIY material cost (20 m²) | £275–£375 |
That’s roughly £14–£19/m² for materials alone, rising to £25–£40/m² once trims, drip edges, and detailing materials come in. If you’re buying a kit and your roof falls between two kit sizes, buy up. Overlaps, upstands, and awkward corners eat material faster than the raw square footage suggests.
Topcoat is the layer not to skimp on. Saving £30 on topcoat thickness can lead to premature chalking, cracking, UV degradation, and £500 or more in repair costs within five years.
How Long Does a GRP Roof Last, and Is It Better Than Felt?
A properly installed GRP roof typically lasts 25–40 years. Some manufacturer-backed systems carry a 20-year product guarantee, with expected service life well beyond 30 years. Industry estimates put 25 years as the minimum before replacement becomes a serious conversation, assuming correct installation and basic upkeep.
Why GRP Outlasts Felt
The seamless finish is the main advantage. Once the resin and matting cure, you have one rigid shell across the roof surface. Felt depends on bonded or torched laps, and those joints are where felt roofs often fail. GRP is also chemically inert once cured, so it doesn’t blister or become brittle in the same way bituminous felt can.
Maintenance Requirements
Very little, genuinely. A yearly visual check and clearing leaf debris around outlets is usually enough. After 15–20 years, a topcoat recoat may be recommended to restore UV protection and refresh the surface. Options include specialist GRP flowcoat or, in some cases, a compatible acrylic-based roof coating. Your installer can advise on the right product.
Where GRP Excels
GRP works especially well on complex shapes: dormer cheeks, bay window tops, angles, and penetrations where jointed systems create more failure points. It costs more upfront, but a seamless finish can avoid the £200–£400 leak repairs that jointed systems often need within their first decade. GRP is also standard for balcony decks with a non-slip surface and walkable flat roofs where foot traffic adds wear.
What Should a GRP Roof Quote Include? A Checklist
The most common reason homeowners overpay for GRP is comparing quotes that aren’t covering the same things. A £75/m² quote and a £95/m² quote can look like a clear choice until one includes deck replacement and the other very much does not.
Essential Inclusions
- Removal and disposal of existing roofing material, if applicable, including skip hire
- Deck inspection with written confirmation of whether boarding replacement is needed
- Supply and installation of all GRP materials: chopped strand mat, resin, and topcoat, with specification and manufacturer named
- All detailing: upstands, trims, drip edges, outlets, and penetration work around pipes or vents
- Clean-up and waste removal on completion
- Written workmanship warranty, including guarantee period and terms
- VAT confirmation, including whether the quote includes VAT at 20%
- Guarantee length, such as 15-year, 25-year, or 40-year specification
Red Flags
Be cautious if a quote is verbal only, has no materials breakdown, makes no mention of deck inspection, or lands well below £70/m². If the roofer can’t name the GRP system or manufacturer they’re using, that’s another warning sign.
Industry pricing shows a 15-year spec starting at around £75/m² and a 40-year spec reaching approximately £110/m². A quote outside that range deserves at least one direct question before you sign anything.
Getting Comparable Quotes
Get at least three quotes and make sure each is based on the same guarantee length and specification. Otherwise, you’re comparing different products and calling it comparison shopping. In London or the South East, allow for the 15–25% regional premium when checking figures against national averages.
For work on habitable spaces or energy-efficiency upgrades, Building Regulations (Part L) generally require an insulated warm roof build-up on extensions over habitable rooms. That makes the £100–£130/m² insulated system figure the realistic starting point for those jobs, not the £70–£90/m² base rate. Ask your installer whether Building Regulations sign-off or inspection applies before you budget for the wrong number.
Quick cost summary: Standard GRP = £70–£90/m² | Premium GRP = £90–£120/m² | Insulated warm roof = £100–£130/m² | Strip & re-deck add £15–£25/m² | DIY materials only = £25–£40/m²
Ready to get a fair price for your GRP roof? Use Fix My Roof to compare free, no-obligation written quotes from qualified GRP installers near you. Make sure every quote is fully itemised, including materials, labour, VAT, and guarantee terms, so you know exactly what you’re comparing before you decide.