Cambridgeshire
Flat-roof rear extensions in Cambridgeshire
Warm flat roofs with lanterns, parapets and long-life membranes. Across Cambridgeshire we handle the whole rear extension: survey, drawings, the planning route, building control and the build. Towns we cover here include Peterborough, Cambridge and Wisbech.
Flat roofs are the usual choice for rear extensions because they stay below first-floor windows and take a lantern neatly. Post-war semis and newer estates are typical of Cambridgeshire, and many have room for a full-width extension. Shrinkable clay is common in the East of England, so foundations near trees and hedges are designed to NHBC-style depth guidance.
How much does a flat-roof rear extension cost in Cambridgeshire?
For Cambridgeshire we work from the East of England rate: £2,010–£3,290 per square metre of new floor, including VAT, standard specification. East of England prices run slightly above our West Midlands baseline; clay soils near trees are the main foundation variable.
| Size | Guide price inc VAT |
|---|---|
| 3 m wide × 4 m deep (12 m²) | £24,000–£39,500 |
| 4 m wide × 5 m deep (20 m²) | £40,500–£65,500 |
| 4 m wide × 6 m deep (24 m²) | £48,500–£79,000 |
Ground conditions, glazing, the roof and how far the house is opened up move the final figure within the range.
Do you need planning permission in Cambridgeshire?
Under England's householder permitted development rules you can usually add 3 metres at the back of an attached house, or 4 metres on a detached house, without a planning application, as long as the extension stays under 4 metres high and its eaves stay under 3 metres where it is within 2 metres of a boundary.
New fabric must meet Approved Document L (2021 edition incorporating 2023 amendments): walls 0.18, roof 0.15 and floor 0.18 W/m²K, windows 1.4 W/m²K or Band B. Under the simple route, new windows, doors and rooflights should not exceed 25% of the extension floor area plus any openings removed; more glass is possible with a whole-house calculation.
Conservation areas, National Parks, National Landscapes and the Broads restrict permitted development, and listed buildings always need listed building consent.
Where in Cambridgeshire do we work?
FAQ
Questions people ask
How long does a flat roof last?
A well-built single-ply or GRP warm roof typically lasts 25 years or more.
Is a flat roof really flat?
No; it is built to falls so water drains to outlets or gutters.
Can I walk on it?
Not as a balcony without planning permission and a guarding design; it can be accessed for maintenance.
Do you cover all of Cambridgeshire?
We cover 11 towns and districts in Cambridgeshire, including Peterborough, Cambridge and Wisbech.
Who builds the extension?
Vetted building teams working under contract to us; your contract is with S&K Property Investments and Improvement Ltd.