An extension quote that starts with “about two thousand a metre” is only useful if both of you mean the same metre and the same finish. Shell-only is not a kitchen-ready room. A side-return in a London terrace is not a rear addition on a semi with a wide garden. This page is the pounds briefing for that rate. It is not a planning decision and it is not a list of builders.
For when the job needs building-control approval, read when you need building regulations. Use the renovation budget tool to split labour, materials and contingency, then open building and conversions when you want a number.
Published UK bands
Checkatrade’s house-extension guide puts a finished single-storey rate at about £1,800–£3,000 per m² excluding VAT, with an average near £2,400. A 20m² example is printed at £40,000–£56,000. A 30m² example is £60,000–£84,000. A 50m² example is £100,000–£140,000. The per-m² table on that page was last updated March 2025; the wider project ranges still circulate as 2026 briefing figures.
The same guide puts a shell-only rate lower, about £1,200–£1,700 per m². A two-storey example based on 60m² of new floor is printed at £108,000–£180,000. Those are not interchangeable with the single-storey finished rate.
| What the guide describes | Published band (excl. VAT) |
|---|---|
| Single-storey, per m² | £1,800–£3,000 (average about £2,400) |
| Shell only, per m² | £1,200–£1,700 |
| 20m² single storey | £40,000–£56,000 |
| 30m² single storey | £60,000–£84,000 |
Sixty-one building cards here mention extensions. Almost all still say a written quote is needed. The only timed rate on a building card is a small-job clock in London, not an extension budget.
London rates are not Leeds rates
London and the South East sit at the top of any published band: party-wall awards, pavement licences, skip permits and restricted access on Victorian terraces all add days before the first brick. A side-return that looks small on plan can still need steel and temporary works. Open builders in London when that is the job, and ask whether the rate is shell or finished.
Manchester, Birmingham and Leeds more often come in nearer the middle of Checkatrade’s £1,800–£3,000 band for a straightforward rear addition — if the ground is clean and the finish is standard. Bristol hills and Georgian neighbours change scaffolding and neighbourly notice. Glasgow and Edinburgh add tenement and listed-building constraints that a per-m² national rate never priced. Cardiff and Nottingham behave like other mid-size cities on labour; ground conditions and drainage still move the first month more than the city name does.
What moves the rate more than floor area
- Ground. Trees, drains, a shared sewer or made-up ground can swallow the contingency before walls go up.
- Structure. Steel in a side-return or a large opening into the existing house is not in a basic rate.
- Glazing. A roof lantern or a wall of sliders can outspend the brickwork.
- Finish. “Warmed shell” versus painted walls, flooring and a fitted kitchen are different contracts.
- Access. No side gate means materials through the house or over a neighbour.
Permitted development can remove a planning application on a smaller rear addition. It does not remove building regulations. Read the building-regulations page before you treat “no planning” as “no paperwork”.
What sits outside a per-m² build rate
Architect or designer fees, structural calculations, planning or lawful-development applications, building-control fees, party-wall surveyors, temporary accommodation, kitchen and bathroom fit-out, landscaping, and VAT are the usual extras. A rate that is silent on VAT is not “including VAT”. Ask which VAT rule they are using on a dwelling extension.
From 1 October 2026, GOV.UK notes that some residential building-control applications may attract a Building Safety Levy. That is a government charge on certain applications, not a builder’s day rate. Check the current GOV.UK page for the work you are actually doing.
What to have on the call
Have a rough internal floor area, whether you mean shell or finished, and whether neighbours share a wall. Ask the builder to price a written specification, not a single rate. Ask who applies for building control and whose name is on the completion certificate.
This site does not email the builder. Open building in London, Manchester or Leeds and use the number on the card.
Questions before you treat this as a bill
How much does a house extension cost per m² in the UK?
Checkatrade’s guide puts a finished single-storey extension around £1,800–£3,000 per m² excluding VAT, average about £2,400. A 20m² example is £40,000–£56,000. A figure here is not a quote from this site.
Is planning the same as building regulations?
No. You might need both, one, or neither in rare exempt cases. Most habitable extensions still need building-control approval even when planning is not required.
Does the per-m² rate include a kitchen?
Usually not. Confirm whether the rate is shell, warmed shell or fully finished, and whether the kitchen is a separate quote.
Where do I find a builder?
Open a building city list and use the phone number on the profile. This site does not send your job.
Need a builder’s number?
Open building and conversions, pick the city, and contact the business yourself.