Flat roof replacement across London

Guide price

£3,350–£5,850

Survey

Free for new and replacement roofs

Quote

Fixed, in writing

Coverage

England, Wales, Scotland, NI

How much does a flat roof replacement cost in London?

Guide prices including VAT at London rates. The fixed price comes after a free survey for new and replacement roofs.

Which flat roofs are common in London?

Flat roofs in London sit on shops with flat-roofed stores below flats above, Victorian and Edwardian terraces with flat-roofed back additions and mansard and dormer loft conversions. The Thames basin is one of the drier parts of Britain at roughly 730 mm of rain a year, but summer heat is the bigger test here: dark membranes on south-facing roofs swing a long way in temperature. Approximate 1991–2020 regional averages based on Met Office data.

Building regulations in England

Replacing more than half of a roof over a heated room usually counts as renovating a thermal element, so it is insulated to current standards and notified to building control. Renovated roofs over heated rooms are insulated to around 0.16 W/m²K where that's feasible, and new extension roofs are built to 0.15 W/m²K. In London the application goes to City of Westminster, London Borough of Camden, London Borough of Islington and 29 other councils. More on the rules.

How long does it take to replace a flat roof?

A garage or single-storey extension roof is usually stripped and re-covered in one to three working days; larger, higher or more detailed roofs take longer. Weather sets the pace, because the deck must be dry before insulation and membrane go down.

We strip only as much as can be made weathertight that day, so the roof is never left open overnight. Expect noise and some vibration during the strip, a skip on the drive (or on the road with a permit) and ladders or a tower against the house. Rooms below stay usable, though it helps to clear shelves near the ceiling. Resin systems such as GRP smell strongly while they cure, so keep nearby windows closed that day. Two-storey roofs need scaffold, which goes up before we start and comes down after sign-off.

Do I need building regulations approval to replace a flat roof?

Often, yes. Replacing the covering of a flat roof over a heated room is usually treated as renovating a thermal element, which brings insulation requirements and, in most cases, approval.

In England, if more than half of that roof is renovated, the whole roof should be upgraded towards a U-value of 0.16 W/m²K for homes (0.18 for non-domestic buildings) where that is technically, functionally and economically feasible, judged against a simple payback of 15 years. Approval comes from building control or self-certification through a registered competent person scheme. Structural changes, or a covering that adds 15% or more to the roof's weight, also need approval.

The other nations differ: most re-roofing in Wales needs approval, Scotland works through building standards and the building warrant, and in Northern Ireland you contact the district council's building control first. An unheated detached garage is not normally a thermal element. Planning permission is not usually needed if the roof looks much the same afterwards, though listed buildings and conservation areas are different. We handle approvals where needed; see building regulations.

Which towns in London do we cover?

• Westminster
• Camden
• Islington
• Haringey
• Hounslow
• Barnet
• Bexley
• Lambeth
• Croydon
• Havering
• Lewisham
• Redbridge
• Southwark
• Bromley
• Ealing
• Hammersmith and Fulham
• Harrow
• Kensington and Chelsea
• Barking and Dagenham
• Brent
• Greenwich
• Hillingdon
• Kingston upon Thames
• Richmond upon Thames
• Sutton
• Waltham Forest
• Enfield
• Hackney
• Newham
• Tower Hamlets
• Merton
• Wandsworth

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