- Guide price
- £3,350–£5,850
- Survey
- Free for new and replacement roofs
- Quote
- Fixed, in writing
- Coverage
- England, Wales, Scotland, NI
London at a glance
- Largest towns
- Westminster, Camden, Islington, Haringey
- Postcode areas
- BR, CR, DA, E, EC, EN, HA, IG, KT, N
- Building control
- City of Westminster, London Borough of Camden, London Borough of Islington and 29 other councils
- Neighbouring areas
- Surrey · Hertfordshire · Buckinghamshire · Berkshire
- Guide price region
- London (+20% on West Midlands rates)
How much does a warm roof upgrade cost in London?
Guide prices including VAT at London rates. The fixed price comes after a free survey for new and replacement roofs.
| Job | Guide price inc VAT |
|---|---|
| Extension (20 m²), EPDM, new deck + insulation | £3,350–£5,850 |
| Extension (20 m²), EPDM with sedum green roof | £5,300–£9,700 |
Which flat roofs are common in London?
Flat roofs in London sit on shops with flat-roofed stores below flats above, mansard and dormer loft conversions and Victorian and Edwardian terraces with flat-roofed back additions. 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.
Can a cold flat roof be converted to a warm roof?
Yes, and it is the usual approach when an older cold roof is re-covered. The old covering is stripped, the deck is checked and replaced where needed, and the vapour control layer, insulation and new waterproofing go on top.
The existing insulation between the joists is assessed at the same time. Leaving it in place can create a cold, unventilated gap that traps moisture, so it is often removed or the build-up is designed so that most of the insulation sits above the deck. We decide this case by case once we can see inside the roof. If the covering is still sound and you are only patching it, the upgrade isn't usually required, and our repair or replace guide explains how to decide between the two.
Will insulating the roof raise its height, and what about doors and upstands?
Yes. A warm roof makes the roof thicker, often by more than 100 mm depending on the insulation and the U-value target. That extra height is the main thing we plan around.
Waterproofing at a wall usually needs to rise about 150 mm above the finished roof surface, so if the roof gets higher, the upstand has to go higher too. That can be a problem where the roof meets a door threshold, a low window sill, a cavity tray or a rooflight kerb. At the edges, trims and fascias are reset to the new level, and gutters may need to move.
Where there isn't enough height, the options include using thinner, higher-performance insulation, lowering the deck where the structure allows, raising the sill or threshold, or, where it is genuinely not feasible to reach the full target, insulating as far as is reasonable and recording why with building control. We work this out at the survey so there are no surprises on the day.
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
Warm roof insulation upgrades in London: questions
Which towns in London do you cover?
All of London. The main towns have their own pages below, and if yours isn't listed we still cover it: send your postcode and we'll confirm.
How much does a warm roof upgrade cost in London?
£3,350–£5,850 for a 20 m² extension roof in EPDM with a new deck and insulation, at London guide rates including VAT. The fixed price comes after a free survey for new and replacement roofs.
Which postcode areas do you cover in London?
All of London, including the BR, CR, DA, E, EC, EN, HA, IG postcode areas. Send your full postcode and we'll confirm.
Is a warm roof worth it on a garage?
On a detached, unheated garage, usually not, as there is no heated space to protect and the thermal rules don't normally apply. On an integral or heated garage, or one being converted into a room, it is.
Does a warm roof stop condensation?
It greatly reduces the risk by keeping the deck warm and placing a vapour control layer on the warm side. Good ventilation in kitchens and bathrooms below still helps.
Can you insulate a flat roof from inside instead?
It is possible, but insulating between or under the joists creates a cold roof, which needs ventilation and carries a higher condensation risk. When the roof is being re-covered anyway, a warm roof from above is usually the better option.
Everything about warm roof insulation upgrades → · All flat roofing in London →