Greater London

Building Regulations for rear extensions in Greater London

Construction drawings, structural calculations and building control through to the completion certificate. Rear extensions in Greater London: we cover 187 towns including Islington, Bexley and Barking, with design, approvals and the build under one contract.

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Building control inspector with a clipboard checking new blockwork walls of a rear extension under construction

Greater London is mostly 1930s semis, short terraces and post-war houses, so full-width single-storey and two-storey rear extensions are realistic on many plots. Some later estates had permitted development rights removed by condition, so we check the planning history first.

What does it cost in Greater London?

As a guide, £2,500–£5,500 including VAT. Your written price follows a measured survey and an agreed design, so it reflects your house, not an average.

What approvals does it need in Greater London?

Every rear extension in England needs Building Regulations approval, whether or not planning is needed. You can use the council's building control service or a registered building control approver, by full plans (checked before work, usually within five weeks) or a building notice, and you get a completion certificate at the end.

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 Greater London do we work?

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FAQ

Questions people ask

Full plans or building notice?

Full plans for most extensions: the design is checked before work starts. A building notice suits only simple jobs.

Who inspects the work?

The council's building control team or a registered building control approver (in Scotland, the council's building standards team).

What is a completion certificate?

The document confirming the work meets the regulations. Keep it; buyers' solicitors ask for it.

Do you cover all of Greater London?

We cover 187 towns and districts in Greater London, including Islington, Bexley and Barking.

Who builds the extension?

Vetted building teams working under contract to us; your contract is with S&K Property Investments and Improvement Ltd.