Cobham at a glance
- Postcode districts
- KT11
- Population
- about 16,724 (GeoNames)
- Council area
- Elmbridge Borough Council
- Building approval
- Elmbridge Borough Council building control, or a registered building control approver
- Nearest main town
- Woking, about 6 miles
- Guide price region
- South East (+10% on West Midlands rates)
Why upgrade to a warm roof in Cobham?
Many flat-roofed extensions and dormers in Cobham were built with little or no insulation, or with a cold roof that was never properly ventilated. Those rooms are often hard to heat in winter and can suffer condensation, mould and, in time, a rotten deck.
In and around Cobham, flat roofs are typically found on newer estates where the first extension roofs are now being replaced, and on lock-up garage blocks on estates. Much of the South East sits in the drier Thames catchment at roughly 730 mm of rain a year, so the usual failures are at joints, upstands and outlets rather than from sheer volume of rain.
How much does a warm roof upgrade cost in Cobham?
Guide price in Cobham: £3,100–£5,350 for a 20 m² extension roof in EPDM with a new deck and insulation, including VAT at South East 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 | £3,100–£5,350 |
| Extension (20 m²), EPDM with sedum green roof | £4,850–£8,900 |
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.
What's included?
- Survey of the deck, joists and existing insulation
- New waterproofing, with a written workmanship guarantee
- Upstands, trims and kerbs reset to the new roof level
- Rigid insulation boards sized to the U-value target
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?
- Esher · 3 mi
- Weybridge · 4 mi
- Leatherhead · 4 mi
- West Molesey · 5 mi
- Sunbury-on-Thames · 5 mi
- Chertsey · 6 mi
Warm roof insulation upgrades in Cobham: questions
Do you cover Cobham?
Yes. Cobham is part of our Surrey coverage, including postcode districts KT11. 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 Cobham?
Where the work needs approval it goes to Elmbridge Borough Council 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 Cobham?
£3,100–£5,350 for a 20 m² extension roof in EPDM with a new deck and insulation, at South East guide rates including VAT. The fixed price comes after a free survey for new and replacement roofs.
How thick does flat roof insulation need to be?
It depends on the insulation product and the U-value target. With common PIR boards, meeting a renovation target usually means well over 100 mm. Thinner, higher-performance boards are available where height is tight.
Can you add insulation over my existing roof without stripping it?
Sometimes, if the existing covering and deck are dry and sound. We will check at the survey and explain the risks, and our overlay or strip guide covers this choice.