Cost FAQ
How much does a rear extension cost in London?
Build: £35,000-£60,000 single-storey, £75,000-£130,000 double-storey, £90,000-£150,000 wrap-around.
Build: £35,000-£60,000 single-storey, £75,000-£130,000 double-storey, £90,000-£150,000 wrap-around.
A single-storey rear extension in London typically costs £2,200 to £3,200 per square metre, so a 20 m² extension usually falls between £44,000 and £64,000 before fit-out.
Glazing is the biggest single variable: a large sliding or bifold system, or a structural glass roof, can add more than the walls it replaces. After that, foundation depth — trees on shrinkable London Clay push a strip footing deeper or into piling — and whether an existing drain or manhole has to be diverted or built over.
Kitchen fit-out is normally excluded from the per-square-metre rate and is often the largest single line in the whole project.
£548 planning where an application is needed, or £249 for larger home extension prior approval. Building control £500 to £1,200. Party wall fees commonly £900 to £1,400 per neighbour, and a mid-terrace rear extension normally engages both sides.
A build-over agreement is needed where the extension crosses a public sewer, and the water authority charges for it.
Stay inside permitted development depth where the layout allows, because the prior approval fee is £249 against £548 and the risk of refusal disappears. Keep the drainage where it is. Choose rooflights over a structural glass roof — the daylight difference is small and the cost difference is not. And fix the layout before the engineer is appointed, so the structural design is not repeated.
A wraparound combines the side return with the rear and typically adds 20 to 30 m². The rate per square metre is similar, but the total is higher and it almost always needs a full householder application rather than permitted development.
A worked Barnet example of how much does a rear extension cost in london?: with 20 conservation areas — the Hampstead Garden Suburb Conservation Area and the Mill Hill Conservation Area among the best known — London Borough of Barnet (Barnet Council) sees how much does a rear extension cost in london? constantly, and there is no borough-wide Article 4 direction, so permitted development generally survives outside conservation areas. Where how much does a rear extension cost in london? pushes a Barnet scheme out of permitted development, the route becomes a £548 application decided in 8 weeks rather than a £249 prior approval in 6 weeks. is governed by the Town and Country Planning Act 1990, the GPDO 2015 and the Building Regulations 2010.
| London rate | £2,200–£3,200 per m² |
|---|---|
| Typical 20 m² extension | £44,000–£64,000 before fit-out |
| Our Essentials package | |
| Our Complete package | |
| Prior approval fee | £249 |
| Building control | £500–£1,200 |
No. Fit-out is normally excluded from the per-square-metre rate.
Sliding systems are usually more expensive per square metre but use fewer frames.
If the extension crosses or comes close to a public sewer, yes.
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