House extension cost UK 2026

A well-designed extension is the single biggest spend most UK homeowners make — and the single biggest opportunity to add space and value. Expect £2,000–£3,200 per m² for a quality single-storey rear in 2026, with London and bespoke specs pushing well above.

How much does this cost in the UK in 2026?

The typical UK price range is £35,000–£180,000, with the average household paying around £65,000. Use the free calculator below to get a personalised estimate.

Free house extension cost uk 2026 calculator

What affects the cost?

• Extension type — single, double, side return or wrap-around all carry different per-m² rates
• Size in m² and number of storeys
• Whether the kitchen moves into the extension (kitchens add £8k–£25k)
• Bi-fold doors and roof lanterns (typical premium £4,000–£10,000)
• Foundations — clay soil, near trees and high water tables all add cost
• Whether you need an architect, structural engineer and party wall surveyor
• Region (London +35 %, North −10 %)

Cost breakdown

Cost by UK region

Regional pricing varies by up to 50 %, mostly driven by labour rates. These multipliers apply to the base UK cost:

Planning permission?

Many extensions are permitted development; double-storey and front extensions almost always need permission

How long does it take?

8–16 weeks typical, plus design and approvals time beforehand.

DIY vs Professional

Difficulty: Pro required. UK building regulations and Part P/Gas Safe rules mean most of this work must be done by registered professionals. Even where DIY is permitted, paying a pro is usually faster and more reliable.

How to save money

• Build under permitted development if possible — saves £200–£400 and 8 weeks
• Keep the kitchen footprint and move only what you must — a new kitchen alone is £10k+
• Use a fixed-price contract, not a labour-and-materials arrangement
• Order high-cost items (kitchens, bi-folds) yourself to avoid 15–25 % builder mark-ups
• Schedule for spring start — autumn builds run into weather delays

How to find a trusted tradesperson

Always get at least three written quotes. Use a vetted UK trade network for peace of mind:

• Checkatrade — vetted local trades with reviews
• MyBuilder — reviewed builders by job type
• Bark — get quotes from local pros

Or use the calculator above to get 3 free quotes direct to your inbox.

Frequently asked questions

How much does an extension cost per m² in 2026?

Expect £2,000–£2,800 per m² for a basic-spec single-storey rear extension outside London. Mid-spec is £2,400–£3,200. London and bespoke can hit £3,500–£5,000 per m². Double-storey is typically only 60–80 % more than single because you share foundations and the roof.

Do I need planning permission for an extension?

Many single-storey rear extensions fall under permitted development (up to 4 m for detached, 3 m for terraced/semi, or 6/8 m under the Larger Home Extension scheme). Double-storey, side and front extensions usually need planning permission. Always check with your local council and consider a Lawful Development Certificate.

How long does an extension take?

A typical 25 m² single-storey extension takes 10–14 weeks on site, plus 8–16 weeks beforehand for design, planning and building control. Allow longer for double-storey and party wall arrangements with neighbours.

Will an extension add value?

Yes — typically 5–15 % uplift, but only if the layout is good and the spec matches the neighbourhood. Over-spec’ing rarely pays back. Kitchen extensions add the most value per pound spent.

What is the cheapest type of extension?

A single-storey rear extension on flat ground with simple foundations is the cheapest at £35,000–£55,000 for around 20 m². Side returns can be similarly priced but often need more bespoke design work.

Get 3 free quotes

Use the calculator above to get an estimate, then submit your details to receive 3 free quotes from vetted local tradespeople. No signup, no spam.

Disclaimer: Prices are guide ranges based on 2026 UK market data. Get quotes from local tradespeople for accurate pricing.