Written by Andrew, Lead Roofer
CORC Certified
Public Liability Insured
Emergency Roof Repairs 24/7
CORC Certified
Public Liability Insured
Emergency Roof Repairs 24/7
Flat roof replacement costs £50-£130 per m² depending on material. Compare EPDM, GRP, and felt prices, plus what affects your quote in 2026.
Flat roofs cover extensions, garages, porches, and bay windows across millions of UK homes. When a flat roof fails, water damage follows quickly. Understanding flat roof replacement costs helps homeowners budget accurately and choose the right material for their property.
This guide covers 2026 pricing for all flat roof materials, explains what affects quotes, and helps you decide between EPDM rubber, GRP fibreglass, and traditional felt systems.
Flat roof replacement costs between £1,500 and £7,500 for most UK homes in 2026. The final price depends on roof size, material choice, and access requirements. Smaller garage roofs sit at the lower end while large extension roofs with premium materials reach the upper range.
| Project Type | Typical Size | Cost Range |
|---|---|---|
| Garage flat roof | 15m² | £1,200–£2,400 |
| Porch or bay window | 5–8m² | £800–£1,500 |
| Rear extension | 20–25m² | £1,800–£3,500 |
| Large extension | 35–45m² | £3,000–£6,500 |
Flat roof replacement pricing includes stripping the old covering, installing new decking where needed, laying the waterproof membrane, and fitting edge trims. Labour accounts for 40–60% of the total flat roof cost, with materials making up the remainder.
Flat roof material choice has the biggest impact on both upfront cost and long-term value. Each flat roofing system offers different lifespans, maintenance requirements, and suitability for specific applications.
| Material | Cost per m² | Lifespan | Best For |
|---|---|---|---|
| Felt (torch-on) | £40–£70 | 15–20 years | Budget projects, temporary solutions |
| EPDM rubber | £50–£90 | 30–50 years | Most residential projects, large roofs |
| GRP fibreglass | £80–£130 | 25–40 years | Balconies, complex shapes, walkable areas |
| PVC membrane | £60–£100 | 25–35 years | Commercial buildings |
Felt flat roofing uses bitumen-impregnated sheets applied with heat. Felt roofing costs less upfront but requires replacement sooner than modern alternatives. Felt flat roofs work for budget-conscious projects where longevity is less critical.
EPDM rubber roofing has become the most popular choice for residential flat roofs in the UK. EPDM flat roof costs offer excellent value when lifespan is considered. EPDM rubber roofing comes in large single sheets, eliminating seams where leaks typically occur.
GRP fibreglass roofing creates a completely seamless, rigid surface that handles foot traffic well. GRP flat roof costs are higher than EPDM but fibreglass roofing excels on balconies, roof terraces, and roofs with complex shapes or multiple penetrations.
PVC membrane roofing is primarily specified for commercial buildings. PVC flat roofing offers good chemical resistance but is less common for residential projects than EPDM or GRP systems.
Flat roof replacement cost scales with roof area, though larger projects often achieve better value per square metre through material and labour efficiencies.
| Roof Size | Felt | EPDM Rubber | GRP Fibreglass |
|---|---|---|---|
| 10m² | £400–£700 | £500–£900 | £800–£1,300 |
| 15m² | £600–£1,050 | £750–£1,350 | £1,200–£1,950 |
| 20m² | £800–£1,400 | £1,000–£1,800 | £1,600–£2,600 |
| 25m² | £1,000–£1,750 | £1,250–£2,250 | £2,000–£3,250 |
| 40m² | £1,600–£2,800 | £2,000–£3,600 | £3,200–£5,200 |
Flat roof replacement for a typical 20m² kitchen extension costs £1,000–£1,800 using EPDM rubber or £1,600–£2,600 for GRP fibreglass. These figures include materials, labour, and standard edge trims but exclude scaffolding, insulation upgrades, or structural repairs.
Several factors influence flat roof replacement quotes beyond basic material and size calculations. Understanding these variables helps explain why quotes vary between contractors.
Roof access significantly affects flat roof costs. Ground-level garage roofs are straightforward to access while rear extension roofs may require scaffolding. Scaffolding hire adds £300–£600 per week to flat roof replacement projects on two-storey properties.
Existing roof removal adds cost when the old covering and decking need stripping. Flat roof removal and disposal typically costs £500–£1,000 depending on roof size and material. Some EPDM systems can overlay existing felt if the deck remains sound.
Insulation upgrades often accompany flat roof replacement. Building regulations require improved insulation when replacing more than 50% of a roof covering. Flat roof insulation upgrades add £800–£1,500 to project costs depending on roof size and required U-values.
Structural repairs increase flat roof costs when decking boards have rotted or joists need attention. Replacing plywood decking adds approximately £25–£35 per m² to flat roof replacement costs.
London pricing runs 10–20% higher than national averages for flat roof replacement. In areas like Fulham and Clapham, where Victorian terrace extensions are common, a typical 20m² kitchen extension roof costs £1,800–£2,600 for EPDM or £2,400–£3,200 for GRP fibreglass.
| Item | Typical Cost |
|---|---|
| Scaffolding hire | £300–£600 per week |
| Skip hire for waste | £200–£400 |
| Old roof removal | £500–£1,000 |
| Insulation upgrade | £800–£1,500 |
| Decking replacement | £25–£35 per m² |
| Guttering repairs | £300–£800 |
Flat roof replacement quotes should itemise these additional costs clearly. Request written quotes specifying exactly what is included before comparing prices between contractors.
EPDM rubber and GRP fibreglass are the two leading flat roof systems for residential properties. Choosing between EPDM and GRP depends on roof use, complexity, and budget priorities.
| Factor | EPDM Rubber | GRP Fibreglass |
|---|---|---|
| Cost per m² | £50–£90 | £80–£130 |
| Lifespan | 30–50 years | 25–40 years |
| Seams | Single sheet (no seams) | Seamless laminate |
| Foot traffic | Walkway pads recommended | Excellent durability |
| Complex details | Requires more trims/adhesives | Moulds around details |
| Appearance | Black rubber finish | Smooth coloured finish |
| Repairs | Patch repairs straightforward | Requires professional repair |
| Best for | Large simple roofs | Balconies and complex shapes |
EPDM rubber roofing offers the best value for most residential flat roofs. EPDM comes in large single sheets up to 15m wide, covering many extension roofs without any seams. EPDM rubber can stretch over 300% without damage, accommodating building movement and thermal expansion without cracking or splitting.
GRP fibreglass roofing creates a rigid, seamless surface ideal for walkable areas. GRP fibreglass excels on balconies, roof terraces, and roofs with skylights or multiple penetrations where EPDM would require numerous trims and joints. GRP flat roofs can be finished in various colours to match property aesthetics.
For a standard rectangular extension roof with minimal foot traffic, EPDM rubber typically offers better value. For balconies, roof terraces, or architecturally complex roofs, GRP fibreglass often proves the superior long-term investment despite higher upfront costs.
Flat roof replacement triggers building regulations requirements in specific circumstances. Understanding when building control approval is needed prevents compliance issues and ensures work meets current standards.
Building regulations apply when replacing more than 50% of a flat roof covering. Flat roof replacement meeting this threshold must achieve minimum thermal performance standards under Approved Document L. The required U-value for flat roof insulation is 0.18 W/m²K for renovation projects.
Building regulations also apply when flat roof replacement involves structural alterations, changing roof height, or converting previously unheated space to heated accommodation.
Building regulations typically don’t apply for minor flat roof repairs covering less than 50% of the roof area, though the repaired section should still meet reasonable thermal standards where practical.
Contractors registered with the NFRC Competent Person Scheme can self-certify certain flat roof replacement works, issuing Building Regulations Compliance Certificates directly without separate local authority inspection. Flat roof replacement by scheme members can offer cost and time savings compared to the standard building control route.
Flat roof insulation meeting building regulations typically requires 100–150mm of rigid PIR insulation board above the deck in a warm roof configuration. LABC guidance provides detailed information on thermal element requirements for homeowners planning flat roof projects.
Flat roofs show specific warning signs when replacement becomes necessary. Recognising these indicators early prevents water damage to ceilings, walls, and building structure.
Ponding water that remains on a flat roof 48 hours after rainfall indicates drainage problems. Persistent ponding accelerates membrane deterioration and increases leak risk. Flat roofs should drain completely within 24–48 hours of rainfall.
Blistering and bubbling on felt flat roofs signals moisture trapped beneath the membrane. Blistered felt roofing often indicates the roof has reached end of life and patch repairs will only provide temporary relief.
Multiple previous repairs suggest a flat roof is failing systematically rather than suffering isolated damage. Flat roofs with numerous patches typically need full replacement rather than additional repairs.
Visible cracks or splits in the membrane allow water ingress. Cracked flat roofing rarely responds well to patch repairs and usually indicates the material has exceeded its serviceable lifespan.
Interior water stains on ceilings below flat roofs confirm water is penetrating the building envelope. Interior damage from flat roof leaks requires prompt attention to prevent timber decay and mould growth.
Roof age provides a useful replacement indicator. Felt flat roofs over 15 years old and EPDM or GRP roofs over 25 years old warrant professional inspection to assess remaining lifespan. Professional roof surveys identify problems before they cause interior damage.
Flat roof lifespan varies significantly by material, installation quality, and maintenance regime. Understanding realistic lifespans helps homeowners plan replacement timing and evaluate material choices.
| Material | Expected Lifespan | With Good Maintenance |
|---|---|---|
| Traditional felt | 10–15 years | 15–20 years |
| Torch-on felt | 15–20 years | 20–25 years |
| EPDM rubber | 30–40 years | 40–50 years |
| GRP fibreglass | 25–35 years | 35–40 years |
| PVC membrane | 20–30 years | 30–35 years |
Felt flat roof lifespan depends heavily on installation quality and UV exposure. South-facing felt roofs typically deteriorate faster than shaded roofs. Felt roofs benefit from reflective coatings that reduce UV damage and extend service life.
EPDM flat roof lifespan makes rubber roofing attractive despite moderate upfront costs. EPDM rubber resists UV degradation, thermal cycling, and weathering without the maintenance felt roofs require. Properly installed EPDM roofs regularly exceed 40 years of service.
GRP flat roof lifespan depends on gel coat condition and installation quality. GRP fibreglass may require topcoat renewal after 15–20 years to maintain UV protection and appearance. GRP roofs installed by trained contractors with quality materials routinely achieve 30+ year lifespans.
Maintenance impact on flat roof longevity is substantial. Annual inspections, prompt debris removal, and clearing blocked outlets extend flat roof lifespan by 5–10 years across all material types. Gutter maintenance prevents water backing up onto flat roof surfaces and causing premature deterioration.
Traditional felt is the cheapest flat roof material at £40–£70 per m² installed. Felt flat roofing costs less upfront than EPDM or GRP but requires replacement after 15–20 years compared to 30–50 years for modern alternatives. EPDM rubber offers better lifetime value for most homeowners despite higher initial costs.
EPDM rubber roofing can sometimes overlay existing felt if the underlying deck remains structurally sound and dry. Overlaying saves removal costs and reduces project time. GRP fibreglass and new felt systems typically require complete removal of existing coverings before installation.
Flat roof replacement takes 1–3 days for most residential projects. A typical 20m² extension roof requires 1–2 days for EPDM installation or 2–3 days for GRP fibreglass. Larger roofs, structural repairs, or complex detailing extend project duration accordingly.
EPDM rubber suits most residential flat roofs, offering excellent value and 30–50 year lifespan. GRP fibreglass is better for balconies, roof terraces, and roofs requiring regular foot traffic. EPDM works best on large simple roofs while GRP excels on complex shapes with multiple penetrations.
Ground-level garage and single-storey extension roofs rarely require scaffolding. Flat roof replacement on two-storey buildings typically needs scaffolding for safe access, adding £300–£600 per week to project costs. Tower scaffolds may suffice for smaller elevated roofs.
Flat roof replacement should include both manufacturer material warranties and contractor workmanship guarantees. EPDM and GRP systems typically carry 20–25 year manufacturer warranties. Reputable contractors provide 10–20 year workmanship guarantees. Insurance-backed guarantees offer additional protection if the installing company ceases trading.
Flat roof replacement costs £50-£130 per m² depending on material. Compare EPDM, GRP, and felt...
Welsh slate lasts 150-200 years, Spanish 75-150 years. Learn what affects slate roof lifespan, signs...