Flat roof replacement cost: what to actually budget
Online flat-roof cost calculators are mostly useless because they ignore the two things that drive 60% of the price: deck condition and access. Here's how we actually quote.
Material cost ballpark (fitted, per m²)
Felt (3-layer torch-on): £75–£110/m². EPDM rubber: £95–£140/m². GRP fibreglass: £110–£160/m². Walked-on systems (terraces, balconies): £140–£220/m². These are all-in fitted prices including strip-back, new insulation if upgrading, membrane, trims, and waste.
What pushes the price up
Rotten deck timbers (very common on 1960s–1980s flat roofs across our patch), insulation upgrade to current building regs, complex upstands and penetrations (rooflights, vents, soil pipes), and access — a first-floor flat roof reached by scaffold is significantly more than a single-storey extension.
What a fair quote looks like
Itemised: strip-and-dispose, deck repair allowance, insulation, membrane material and labour, trims and upstand details, scaffold/access, VAT. If your quote is one number with no breakdown, ask for the breakdown — that's how you compare apples to apples.
Typical real-world examples from our jobs
20m² single-storey rear extension EPDM with insulation upgrade in Hampton: ~£2,400–£3,200. 12m² dormer roof in EPDM with scaffold in Teddington: ~£2,000–£2,800. 35m² walked-on terrace in GRP in East Sheen: ~£5,500–£7,500.
FAQs
Most domestic flat roofs are a 1–3 day job. Larger or more complex roofs (walked-on systems, multiple upstands) can take a week.
Re-covering an existing flat roof usually triggers building regs if more than 25% of the roof is being renewed — which most replacements are. We handle the notification and sign-off as part of the job.
We can give a rough ballpark from photos, but a fixed-price quote needs an on-site inspection — flat roofs hide too much under the membrane to quote remotely with confidence.
Related reading
More on roof repairs and the jobs that usually come with it.
- Moss on a roof: does it actually matter?Repairs & problems
- Ridge tile replacement: mortar bedding vs dry-fix ridge
- New roof cost: what a re-roof really costs in 2026
- Lead alternatives: when they work and when they don'tMaterials & systems
Looking for something specific? See our roofing services, cost guides, common roof problems or the areas we cover.
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Family-run and Hampton-based. Tell us what you're seeing on the roof and we'll come and look properly before quoting.