Flat roof prices in London vary by material, roof size, access, and property requirements. This guide is based on real Knights Roofing projects completed across London in 2025-2026, so you can budget accurately before you get a quote.
Prices include materials, labour and VAT, based on residential installations in London, January 2026. Typical project costs range from £1,200 to £6,000 depending on size and material.
Whether you're replacing an old felt roof, considering EPDM rubber, or exploring GRP fibreglass, several factors shape what you'll actually pay. For repairs rather than a full replacement, see our flat roof repair page instead — most localised damage doesn't need a full replacement.
EPDM, GRP, felt and PVC have different price points and lifespans
Larger roofs benefit from economies of scale
Central London commands 20–30% premium pricing
Difficult access increases labour costs
Deck board replacement adds to total cost
Costs based on standard installations in London, 2026. Actual prices vary by project specifics — a free survey gives you an exact figure.
Cost: £50–£90 per m² | Lifespan: 40–50 years
Best for most residential projects · very low maintenance
Cost: £80–£130 per m² | Lifespan: 30–40 years
Ideal for balconies and complex shapes · low maintenance
Cost: £40–£70 per m² | Lifespan: 15–20 years
Budget projects and temporary solutions · moderate maintenance
Cost: £60–£100 per m² | Lifespan: 25–35 years
Commercial buildings · low maintenance
Felt has the lowest upfront cost but the shortest lifespan — a 30m² felt roof runs around £1,500 now plus another £1,800 in 15–20 years, versus roughly £2,200 once for EPDM lasting 45+ years. Book a free survey and we'll recommend the option with the best lifetime value for your roof.
GRP adds multiple resin coats plus a colour topcoat and anti-slip finish.
Felt uses two or three torch-on layers depending on the specification.
EPDM is either fully adhered or mechanically fastened, depending on the roof.
Small roofs carry higher per-m² costs due to minimum callout charges; larger roofs benefit from economies of scale.
| Roof size | EPDM | GRP | Felt | PVC |
|---|---|---|---|---|
| Small garage (15m²) | £1,200–£1,600 | £1,800–£2,400 | £900–£1,300 | — |
| Typical extension (25m²) | £1,800–£2,600 | £2,800–£3,800 | £1,400–£2,000 | £2,000–£2,800 |
| Large extension (40m²) | £2,800–£4,200 | £4,200–£6,000 | £2,200–£3,200 | £3,000–£4,400 |
| Commercial unit (80m²) | £5,200–£7,800 | £7,500–£11,200 | £4,000–£6,000 | £5,600–£8,400 |
PVC is rarely specified for roofs under 25m² — figures not applicable at garage scale. Get a free, itemised quote for your exact roof.
From Knights Roofing projects across London, 2024–2026.
Beyond the core installation, these are the most common extras — flagged upfront in a proper quote rather than added later.
Planning permission is rarely required for flat roof replacement — it typically counts as repair and maintenance. Listed buildings and conservation areas may have restrictions. Building Regulations compliance under Approved Document L applies to most projects; we handle this as part of the job.
At Knights Roofing, we provide written quotations within 2–3 working days of inspection, clearly detailing costs, materials and timelines. Request your free inspection.
The average price ranges from £50 to £130 per square metre depending on material. For a typical 25m² extension, expect £1,250–£3,250. EPDM offers the best value at £50–£90 per m², GRP costs £80–£130 per m², and felt ranges from £40–£70 per m². These include materials, labour and VAT — total cost also depends on access, structural condition and insulation requirements.
Traditional torch-on felt has the lowest upfront cost at £40–£70 per m², but only lasts 15–20 years compared to EPDM's 40–50 years. On a 30m² roof, felt costs around £1,500 now plus £1,800 again in 15–20 years (£3,300 lifetime), while EPDM costs about £2,200 once and lasts 45+ years — better long-term value despite the higher initial price.
EPDM: £1,400–£2,000. GRP: £2,000–£2,800. Felt: £1,000–£1,500. These assume existing deck boards are in good condition — insulation upgrades, structural repairs or scaffolding add to the total.
Yes, typically 30–40% less — EPDM costs £50–£90 per m² versus GRP at £80–£130 per m². Both perform well; GRP is generally preferred for roofs that double as balconies, while EPDM offers better value for standard flat roofs.
Usually not — it's normally covered by permitted development rights. Exceptions: listed properties, conservation areas with added restrictions, significant changes to roof height or structure, or new rooflights overlooking neighbouring properties. You will still need to comply with Building Regulations, which we handle as part of the job.
Small garage (15–20m²): 1–2 days. Standard extension (25–35m²): 2–3 days. Large extension (40–60m²): 3–5 days. Commercial (80m²+): 5–10 days. This assumes good weather and no major structural surprises.
Current Building Regulations require improved thermal performance when replacing a flat roof, so insulation is typically recommended and often required for compliance. Always confirm in your quote whether it's included and to what specification.
Usually covered: storm damage, fire, accidental damage, vandalism. Usually not covered: wear and tear, age-related deterioration, lack of maintenance, or pre-existing problems. Document the damage with photographs and notify your insurer before starting work — most policies require multiple quotes.
EPDM rubber: 40–50 years. GRP fibreglass: 30–40 years. Single-ply PVC: 25–35 years. Traditional felt: 15–20 years. Proper installation and regular maintenance help roofs reach the top of these ranges.
Most quotations include VAT at the standard 20% rate. Reduced VAT (5%) may apply if the building has been empty for 2+ years and is being renovated, you're converting a non-residential building to residential use, or the work is for a registered charity. Standard occupied residential replacements are charged at 20%.
Mainly labour costs, access challenges (parking restrictions, congestion, limited space), higher demand for skilled contractors, and stricter enforcement of Building Regulations and party wall requirements. Central London (Zones 1–2) sits at the top of the range, with costs easing in outer London.
Written, itemised quote within 2–3 working days. No obligation.
Get your free quote Call 020 7126 8439
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