Cost of Single Storey Extension in Westminster (2026)
Expect to pay somewhere between £2,520 and £4,480 for single storey extension in Westminster, per m². Greater London prices are noticeably above the UK average. Get at least three written quotes before committing — it's a 10 to 15 percent swing in either direction for not much effort.
About single storey extension in Westminster
Westminster is a large city of around 261,000 in Greater London. The housing is mostly South West London housing leans Victorian and Edwardian with pockets of 1930s semis and modern flats. That matters: older properties usually mean more pipework, rewiring and retrofit surprises, while newer builds in districts like SW1, W1, WC2 tend to be quicker jobs with standardised fittings. Local trade prices sit on the expensive side for UK trade work. That's mostly wage levels plus the cost of running a van and a yard in and around Greater London.
London's the deepest trade market in the country, and also the priciest. ULEZ, congestion charge, parking permits, higher van insurance — it all feeds into the day rate. Most decent firms charge a callout and central boroughs run a clear premium over zones 4 and 5. Book two to three weeks ahead if you can.
Building jobs are labour-heavy, and materials have moved fast — brick, timber, steel, insulation and board are all 20 to 40 percent up on pre-2022. FMB and TrustMark are your best signposts for a proper builder. On anything bigger than a loft conversion, get a Building Control officer involved from day one; fixing non-compliance later costs a fortune.
Single Storey Extension cost breakdown in Westminster
Simple rear extension with standard finish
Open-plan kitchen extension with bi-fold doors
Wrap-around or glazed extension with lantern roof and structural steels
What affects the price of single storey extension in Westminster?
- Ground conditions and foundation depth
- Glazing ratio (bi-folds, roof lights)
- Kitchen refit included
- Structural steels and knock-through
- Planning permission vs PD
Westminster vs the UK average
Westminster sits in the building & construction market at a cost multiplier of 1.40× the UK national average. That puts Westminster single storey extension prices at £2,520–£4,480 versus the UK average of £1,800–£3,200 per m².
Single Storey Extension cost calculator — Westminster
Estimate based on live 2025 UK trade pricing. Always get 3 written quotes before committing.
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What's typically included in a single storey extension quote
- Foundations and drainage
- Brick and block shell
- Roof and glazing
- First and second fix
- Plaster and decoration
Frequently asked questions
How much does single storey extension cost in Westminster?
Budget £2,520 to £4,480 per m² for single storey extension in Westminster. Prices here are around 40% more expensive than the UK average. What moves a quote inside that range is mostly building contractor day rates in Greater London and the specific material list for your job.
How long does single storey extension take in Westminster?
A straightforward single storey extension job in Westminster runs to 10–16 weeks. You can lose days to things outside the contractor's control — parts on backorder, awkward access, or a firm slotting your job around existing bookings. Ask for a start date and expected finish up front.
What's included in the price of single storey extension in Westminster?
A proper single storey extension quote in Westminster should cover: Foundations and drainage; Brick and block shell; Roof and glazing; First and second fix; Plaster and decoration. If any of those aren't itemised on your quote, push back and ask. A written guarantee with a clear warranty period is reasonable to expect on this kind of work.
Is single storey extension cheaper in Westminster than the UK average?
Single Storey Extension in Westminster runs around 40% more expensive than the UK average. The UK-wide benchmark for this job is £1,800 to £3,200 per m²; Westminster quotes tend to land between £2,520 and £4,480. Handy to know what the average actually looks like before you price round.
Do I need planning permission for single storey extension in Westminster?
Most rear extensions fall under Permitted Development (up to 6m terraced/8m detached with Prior Approval). Side extensions and Article 4 areas require full planning. If the property sits in a conservation area or is listed, ring Greater London Council before you book anything in. It's a free call and saves a world of grief later.
See all single storey extension prices across the UK or browse all tradespeople costs in Westminster.