House extensions in London
Single and double storey rear and side extensions on London terraces and semis — from the first site visit through to building control sign-off, with one team and one price.
From £2,100 per m² · typically 10–16 weeks on site
What the price actually includes
An extension quote from us covers the whole build, not just the shell. Foundations and drainage diversions, steel beams designed by an engineer, brickwork matched to your existing stock, roof and insulation, windows and doors, first and second fix electrics and plumbing, plaster, and making good where the new work meets the old house.
What sits outside the price is listed clearly rather than buried: architectural drawings, structural calculations, planning fees, party wall surveyor fees, and your choice of kitchen or flooring. If you already have any of these, we price around them.
Do you need planning permission?
Many single-storey rear extensions on a house fall under permitted development, which means no planning application. The usual limits are 3m for a terrace or semi and 4m for a detached house, extendable under the larger home extension scheme with a neighbour consultation. Flats never get permitted development, and conservation areas and previously extended properties are treated differently.
We will tell you which category you are in at the site visit, before you have spent anything on drawings.
Party walls
Almost every London extension touches a shared wall or digs within three metres of a neighbour’s foundation. That triggers the Party Wall Act, and notices have to be served two months before work starts on a wall, or one month for excavation. We flag this at quote stage and tell you exactly which notices you need and when, so the start date does not slip.
How long it takes
A straightforward single-storey rear extension runs 10 to 16 weeks on site. Double storey is 16 to 22 weeks. Add roughly six to ten weeks before that for drawings, building control and party wall notices if you are starting from nothing.
Common questions
How much does an extension cost per square metre?
Around £2,100 per m² is a realistic starting point for a good specification in London, and we are not VAT registered so there is no VAT on our labour. Ground conditions, drainage runs, glazing choices and the roof design move that number, which is why the quote follows a site visit rather than a phone call.
Can we stay in the house during the build?
For a single-storey rear extension, usually yes. There will be a week or two around the knock-through when the kitchen is out of action, and we will tell you when that window is so you can plan around it.
Who deals with building control?
We do. We submit the notice, book each inspection and meet the inspector on site, then hand you the completion certificate at the end. You will need that certificate when you sell the house.
What if you find something unexpected under the floor?
It happens — old drains, poor foundations, asbestos in an old outhouse. Anything we cannot see at the site visit is priced as a provisional sum in the quote. If it turns out to cost more, we show you the cost in writing and get your agreement before carrying on.
Get an extension quote
Free site visit. Written price in 48 hours.
Thinking about an extension?
Book a free site visit this week. We will tell you what is possible, what it costs, and whether you need planning — before you spend a penny on drawings.