What is a single-storey extension?
A single-storey extension is a ground-floor addition, usually at the rear of a house, that enlarges a kitchen, living or dining space. Most are built with cavity walls on concrete foundations and finished with a flat roof and roof lantern or a pitched tiled roof.
How much does a single-storey extension cost in Hampstead?
In Hampstead, a single-storey extension typically costs £2,550–£3,750 per m² of floor area, including VAT at 20% (standard rate). For a typical 20 m² project that is roughly £51,000–£75,000. We start from a UK-wide guide and adjust it for London, where labour and materials are typically about 30% above average. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (14 m²) | £35,500–£52,500 |
| Typical project (20 m²) | £51,000–£75,000 |
| Larger project (28 m²) | £71,500–£105,000 |
| Rate per m² | £2,550–£3,750 |
What moves the price most:
- How much of the existing house is opened up
- Roof type and the size of any lantern or roof windows
- Ground conditions and foundation depth
- Floor area and the length of new wall
For a figure based on your own measurements, try the guide price tool, then book a free home visit for a fixed quote.
Do you need planning permission for a single-storey extension in Hampstead?
The approval route for Hampstead is set by planning law in England. In England a single-storey rear extension is often permitted development: broadly up to 3 metres deep on a semi-detached or terraced house and 4 metres on a detached house, no higher than 4 metres, with eaves no higher than 3 metres within 2 metres of a boundary, and covering no more than half the garden. The larger home extension scheme allows up to 6 or 8 metres if you notify the council first and neighbours have a chance to comment. In conservation areas, National Parks and National Landscapes the larger home extension route, side extensions and cladding are not permitted development. Flats and houses whose rights have been removed need a planning application, and listed buildings need listed building consent.
Where work involves a shared wall, building on the boundary, or digging foundations within 3 metres of a neighbour’s building and deeper than its foundations (or within 6 metres for deeper work), the Party Wall etc. Act 1996 applies and notices must be served before work starts.
If the answer is not clear-cut, we can apply for formal confirmation before you commit to the build.
What we handle
Handled as part of most single-storey extensions:
- Knock-through to the existing house with steel beams
- Cavity walls, insulation and roof to current building regulations
- Building control inspections and completion certificate
- Structural calculations for steels and lintels
- Doors, windows and roof glazing installed
- Foundations, drainage and any build-over agreement
How long does it take?
The build itself usually takes 10 to 14 weeks on site for a typical rear extension, after approvals. Allow time beforehand for drawings and approvals, usually 6 to 12 weeks.
Building in Hampstead
Space is at a premium in London, so homeowners often build out into the side return or up into the roof rather than move.
If your home is in Hampstead or close by in Highgate, Golders Green and Camden, a free home visit is the first step.
How it works
- 01
Free visit
We look at the property, talk through what you want and measure up. There is no charge and no obligation.
- 02
Drawings and written quote
We prepare the design and give you a written, itemised quote with inclusions and exclusions.
- 03
Approvals in place
We handle planning, building control and neighbour notices before work starts.
- 04
Build and sign-off
We run the build to a written programme and hand over the completion certificate.
Questions about single-storey extensions in Hampstead
How much does a single-storey extension cost in Hampstead?
In Hampstead, a single-storey extension typically costs £2,550–£3,750 per m² of floor area, including VAT at 20% (standard rate). A typical 20 m² project comes to roughly £51,000–£75,000. Your fixed price depends on the survey and drawings.
Do I need planning permission for a single-storey extension?
Not always. Many small rear extensions are permitted development, within limits on depth, height and how much of the garden is covered. The limits depend on which nation you live in and on protected areas such as conservation areas, and flats or houses whose rights have been removed need an application. We check this at the survey and can apply to the council for formal confirmation.
Is VAT charged on an extension?
Yes. Building work on an existing home is standard-rated, so VAT at 20% applies. Our guide prices include it.
How long does a single-storey extension take in Hampstead?
Typically 10 to 14 weeks on site for a typical rear extension, after approvals. Design and approvals beforehand usually take 6 to 12 weeks.
Can I stay in the house during the build?
Usually yes. We build the shell before opening up the back wall, so the house stays weathertight for most of the job. There will be a few weeks when the kitchen or back room is out of use.