Greater London

Flat-roof rear extensions in Greater London

Warm flat roofs with lanterns, parapets and long-life membranes. We design and build rear extensions across Greater London, from Islington and Bexley to Barking, covering single-storey kitchen extensions, two-storey additions, side returns and wraparounds.

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Flat roof of a new rear extension with a grey membrane, aluminium coping and a large roof lantern

Flat roofs are the usual choice for rear extensions because they stay below first-floor windows and take a lantern neatly. 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.

How much does a flat-roof rear extension cost in Greater London?

Guide prices for a flat-roof rear extension in Greater London start from our London rate of £2,470–£4,030 per square metre, including VAT. London prices sit at the top of our range because of labour rates, access through the house, parking suspensions and skip licences.

Flat-roof rear extension guide prices in Greater London
Size	Guide price inc VAT
3 m wide × 4 m deep (12 m²)	£29,500–£48,500
4 m wide × 5 m deep (20 m²)	£49,500–£80,500
4 m wide × 6 m deep (24 m²)	£59,500–£96,500

These are guide ranges; the written quote after the survey is the figure that counts.

Do you need planning permission in Greater London?

In England a single-storey rear extension can often be built under permitted development: up to 3 metres beyond the original rear wall of an attached house, or 4 metres on a detached house, no higher than 4 metres, with eaves no higher than 3 metres if any part 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 Greater London do we work?

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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 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.