Ground floor extension in London

Q: How much does a ground floor extension cost in London?

Our current prices are £40,000–£250,000 (October 2026), depending on the shape and size. The cost table on this page shows each option and what the price includes.

Q: Side return, rear or wraparound: which should I choose?

Choose a side return if the kitchen is narrow and the garden small, a rear extension if you have garden depth and want one deep room, or a wraparound if you want the most space on one level and can accept a full planning application. We compare all three on the survey.

Q: Do I need planning permission for a ground floor extension?

A side return or a modest rear extension often does not need planning permission, because it falls under permitted development; a wraparound almost always does. Conservation areas, Article 4 directions, flats and listed buildings always need a full application.

Q: How long does a ground floor extension take?

A ground floor extension takes six to eight months in total: 12–14 weeks of design and planning, then 12–20 weeks on site depending on size.

Q: Can I add a loft conversion at the same time?

A loft conversion can be built at the same time as a ground floor extension. Doing both together means the scaffolding, site set-up and disruption are shared, and we design them as one scheme so the structure and services line up.

Q: Does a ground floor extension need a party wall agreement?

A ground floor extension almost always needs a party wall agreement, because the new walls or foundations are on or near the boundary. We draft and serve the notices the Party Wall etc. Act 1996 requires, and can appoint the surveyor.

Side return, rear, or both: a ground floor extension that gives your London home the open-plan living space it was never built with. One team, priced in writing.

A ground floor extension with Build Team costs £40,000–£250,000 (October 2026); the table below shows what each price includes. The price depends mainly on the shape: a side return, a rear extension or a wraparound. Allow 12–14 weeks for design and planning, then 12–20 weeks on site. Side returns and modest rear extensions are usually permitted development; wraparounds need a full application. Every Build Team extension carries a 3-year structural guarantee plus 2 years’ defects liability.

What is a ground floor extension?

A ground floor extension is any single-storey addition at the back or side of the house: a side return that fills the alleyway beside the outrigger, a rear extension that pushes the back wall into the garden, or a wraparound that does both. On a London terrace it almost always becomes an open-plan kitchen, dining and living space with wide doors to the garden.

Which shape is right depends on the plot: a narrow kitchen and a small garden point to a side return; a long garden and the wish for one deep room point to a rear extension; a family wanting the most space on one level points to a wraparound. We look at all three on the first survey and show you what each gives you and what each costs.

How much does a ground floor extension cost in London? (October 2026)

Option	From	To	Per m²	Includes
Side return (10–18 m²), all-in	£80,000	£140,000	£6,500–£8,500	Fills the side alleyway; keeps the garden
Rear extension (15–25 m²), all-in	£75,000	£150,000	£4,200–£6,500	Extends the back wall into the garden
Wraparound (20–35 m²), all-in	£130,000	£250,000	£5,500–£7,500	Side and rear together; largest footprint
Shell only (any shape), build cost	£40,000	£160,000	£2,500–£5,000	Structure, roof, glazing, first-fix services; before fees, VAT, kitchen

Prices updated October 2026. All prices include VAT unless stated.

Try our extension cost calculator

How long does it take?

A ground floor extension takes six to eight months from the first design meeting to handover, depending on shape. Design and planning take 12–14 weeks; the build takes 12–20 weeks.

Weeks 1–2: measured survey, concept design (we compare side return, rear and wraparound)
Weeks 3–12: Lawful Development Certificate or full planning application
Weeks 13–14: Building Regulations drawings, structural calculations, party wall notices
Weeks 15–34: build, with a named Build Manager on site

What adds time: a full application rather than permitted development, two party wall awards on a mid-terrace, drainage under the new footprint, and structural-glass roofs with long lead times.

Will it need planning permission?

Planning permission for a ground floor extension depends on the shape: a side return or a modest rear extension usually does not need it, and a wraparound does. Class A of Schedule 2, Part 1 to the Town and Country Planning (General Permitted Development) (England) Order 2015 sets the limits. To the rear, a single-storey extension can go 3 metres deep on a terrace or semi and 4 metres detached, or 6 and 8 metres under prior approval. To the side, it can be up to half the width of the house. Both must stay under 4 metres high. A wraparound goes beyond the side and rear walls at once, so it falls outside Class A and needs a full application.

Any shape needs a full application in a conservation area, under an Article 4 direction (parts of Hackney, Camden, Islington, Lambeth and Westminster), or for a flat or a listed building. We confirm which route your address is on before we draw, and run it for you. If you are building near a boundary, see our Party Wall service.

What can go wrong, and how we handle it

The final bill will be higher than the quote.

The build price is fixed in writing before you sign, whichever shape you choose. The price moves only if you change the design, and you approve each change and its cost before the work is done. The unknowns on a ground floor job are below ground, in the foundations and the drainage under the new floor, and the quote carries a contingency for them.

I'll pick the wrong shape and regret it.

On the first survey we draw all three options on your plan and show you what each gives you in space, light and garden, and what each costs. You choose with the numbers in front of you, not from a brochure.

The builder will hand the job to subcontractors and vanish.

One Build Manager runs your extension from the first day on site to snagging. That person is a Build Team employee and is on site through the whole job. Each trade on site is one of our regular teams rather than whoever happens to be free.

How Build Team designs and builds your ground floor extension

Build Team works on a ground floor extension in two fixed-price stages: design, then build. The Design Phase starts by drawing the side return, rear and wraparound options on your own plan, so you choose the shape with the costs in front of you. It covers the survey, drawings, planning and Building Regulations, and Ready to Build design fees for ground floor work start from £3,995. You can use the drawings with any builder.

Once you sign the build contract, a named Build Manager runs the site and reports to you every week. Because design and build sit in one company, the person who decided where the new steels and drains go is on hand when the builders open up the back of the house.