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 choose a green roof in Cobham?
Rainwater from flat roofs in Cobham runs off quickly in heavy showers. A green roof holds some of that water back and releases it more slowly, which is one reason some owners and developers choose one. The flowering sedum also draws in bees and other insects.
In a town like Cobham, flat roofs are commonly found on shops with flat-roofed rear stores below flats or newer estates where the first extension roofs are now being replaced. 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 green roof cost in Cobham?
Guide price in Cobham: £4,850–£8,900 for a 20 m² insulated extension roof finished as a sedum green roof, 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 with sedum green roof | £4,850–£8,900 |
| Extension (20 m²), EPDM, new deck + insulation | £3,100–£5,350 |
Can my flat roof take the weight of a green roof?
Not every roof can, which is why we check the structure before quoting. A sedum roof is light compared with an intensive garden, but its growing medium holds water, and a saturated build-up adds significant weight to the roof.
We look at the joist sizes, spans and spacing, the condition of the deck and what the roof sits on. On a recently built extension with generously sized joists, an extensive green roof may be straightforward. On an older garage or a roof with undersized or rotten timbers, the structure may need strengthening, or a structural engineer's calculation may be needed before we can go ahead.
In England, a new roof covering that adds 15% or more to the weight of the roof triggers building control approval, and a green roof will often fall into that category. We handle building control where it is needed. The building regulations page covers the approval routes in each nation.
What's included?
- Warm or inverted build-up to suit the roof
- Gravel strips kept clear around edges and outlets
- Drainage layer, filter and lightweight growing medium
- Structural check of joists, deck and supports
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
Green and sedum roofs 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 green roof cost in Cobham?
£4,850–£8,900 for a 20 m² insulated extension roof finished as a sedum green roof, at South East guide rates including VAT. The fixed price comes after a free survey for new and replacement roofs.
Can a green roof have a rooflight in it?
Yes. The rooflight sits on a raised upstand with a gravel strip around it, so the planting stays clear of the glazing and the upstand stays visible and dry.
Can you put a sedum roof on a garage?
Often, yes, if the structure is strong enough. Many older garage roofs have light timbers, so a structural check comes first and strengthening may be needed.