Barnet at a glance
- Postcode districts
- N20, N11, N14, N12, EN4, N3, EN5, NW7 and 1 more
- Council area
- London Borough of Barnet
- Building approval
- London Borough of Barnet building control, or a registered building control approver
- Guide price region
- London (+20% on West Midlands rates)
Why upgrade to a warm roof in Barnet?
Kitchen extensions in Barnet, as elsewhere, produce a lot of moisture from cooking. Under a cold flat roof, that moisture can condense on the deck. A warm roof keeps the deck warm and puts a vapour control layer in the way, which lowers the risk considerably.
Around Barnet, flat roofs are common on Victorian and Edwardian terraces with flat-roofed back additions and on kitchen extensions and roof terraces behind period houses. 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.
How much does a warm roof upgrade cost in Barnet?
For Barnet we use London rates: £3,350–£5,850 is the guide for a 20 m² extension roof in EPDM with a new deck and insulation, VAT included. 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 |
Do I have to insulate my flat roof when I replace it?
Usually, yes, if the roof is over a heated room and you are replacing more than half of its covering. In England, Wales and Northern Ireland, that counts as renovating a thermal element, so the roof should be upgraded to the renovation standard where that is technically, functionally and economically feasible.
The rules don't usually apply to patch repairs, or to an unheated, detached garage. The target U-value depends on where you live:
| Nation | Roof renovation target |
|---|---|
| England | 0.16 W/m²K (homes), 0.18 (non-domestic) |
| Wales | 0.16 W/m²K |
| Scotland | Section 6 framework, with a domestic benchmark of 0.12 W/m²K pursued as far as reasonably practicable |
| Northern Ireland | 0.18 W/m²K |
A new extension roof has a tighter target than a renovation: 0.15 in England and 0.13 in Wales. The economic test in England's guidance is a simple payback within 15 years. We handle building control or building standards where it is needed. The building regulations page sets out the approval routes in each nation.
What's included?
- Rigid insulation boards sized to the U-value target
- New waterproofing, with a written workmanship guarantee
- Upstands, trims and kerbs reset to the new roof level
- Building control or building standards handled where needed
Building regulations in England
Replacing more than half of a flat roof over a heated room usually counts as renovating a thermal element, so the roof is insulated to around 0.16 W/m²K where that's technically and economically feasible, and the work is notified to building control: the council or a registered building control approver, unless a registered competent person self-certifies it. A roof on a new extension is built to 0.15 W/m²K. Patch repairs, and most unheated detached garages, don't trigger the upgrade. Structural changes, or a new covering that adds 15% or more to the roof's weight, also need approval. More on the rules.
Which nearby areas do we also cover?
Warm roof insulation upgrades in Barnet: questions
Do you cover Barnet?
Yes. Barnet is part of our London coverage, including postcode districts N20, N11, N14, N12, EN4, N3 and 3 more. Surveys and roofs are carried out by vetted roofing teams working under S&K Property Investments and Improvement Ltd.
Who checks building regulations for a flat roof in Barnet?
Where the work needs approval it goes to London Borough of Barnet building control, or a registered building control approver. We tell you at the survey whether your job needs it and deal with the paperwork as part of the quote.
How much does a warm roof upgrade cost in Barnet?
£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.
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.