Grantham at a glance
- Postcode districts
- NG31
- Population
- about 44,580 (GeoNames)
- Council area
- South Kesteven District Council
- Building approval
- South Kesteven District Council building control, or a registered building control approver
- Guide price region
- East Midlands (−2% on West Midlands rates)
What makes a good extension roof in Grantham?
Condensation drives some replacements in Grantham. Older extension roofs were often built cold, with insulation between the joists and no reliable vapour control. Warm air from the kitchen reaches the cold deck, moisture builds up and the timber suffers. A warm roof deals with the cause, not just the stain.
Grantham's flat roofs are mostly on lock-up garage blocks on estates, with plenty on shops with flat-roofed rear stores below flats too. The East Midlands is drier than the west of Britain, so most flat roofs here fail through age, UV and poor detailing at upstands rather than sheer rainfall.
How much does a new extension roof cost in Grantham?
At East Midlands guide rates, a 20 m² extension roof in EPDM with a new deck and insulation comes to £2,750–£4,800 including VAT. 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 | £2,750–£4,800 |
| Extension (20 m²), GRP, new deck + insulation | £2,950–£5,300 |
| Extension (20 m²), EPDM, insulation + 1 rooflight upstand | £2,950–£5,150 |
| Single garage (18 m²), EPDM rubber | £1,550–£2,750 |
Does an extension roof replacement need building regulations?
Usually, yes. An extension roof over a heated room is a thermal element, so replacing most of it typically brings insulation requirements and an approval route.
In England, renovating more than half of the roof means upgrading it towards 0.16 W/m²K where that is technically, functionally and economically feasible. The approval comes from building control or a competent person scheme. A brand-new extension roof is designed to 0.15. Wales usually requires approval for most re-roofing, with a renovation target of 0.16 and a new-extension target of 0.13. Scotland handles this through building standards and the warrant process, and Northern Ireland through district council building control.
Planning is not normally needed to re-cover an extension roof that looks broadly the same afterwards. Turning the roof into a terrace is another matter. We handle building control where the job needs it; see our building regulations page.
What's included?
- Free survey of the roof, abutment and room below
- Building control handled where needed, and a written workmanship guarantee
- Staged strip-out so the room stays weathertight
- New deck, vapour control layer and warm-roof insulation
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?
- Sleaford · 11 mi
- Newark-on-Trent · 13 mi
- Melton Mowbray · 14 mi
- Stamford · 19 mi
- West Bridgford · 20 mi
- Arnold · 21 mi
Extension and kitchen roofs in Grantham: questions
Do you cover Grantham?
Yes. Grantham is part of our Lincolnshire coverage, including postcode districts NG31. 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 Grantham?
Where the work needs approval it goes to South Kesteven District 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 new extension roof cost in Grantham?
£2,750–£4,800 for a 20 m² extension roof in EPDM with a new deck and insulation, at East Midlands guide rates including VAT. The fixed price comes after a free survey for new and replacement roofs.
Can you keep my existing roof lantern?
Often, if the lantern itself is sound. We lift it, rebuild the kerb, dress the new membrane up the upstand and refit the lantern.
Why does my extension ceiling get damp in winter if the roof isn't leaking?
That is often condensation in a cold roof, where warm, moist air reaches the cold underside of the deck. A warm-roof replacement with a vapour control layer usually solves it.