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 Hounslow?
In Hounslow, 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. The guide for Hounslow reflects typical costs in London, roughly 30% above the UK-wide figure. 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 |
The main things that change the cost:
- Ground conditions and foundation depth
- Floor area and the length of new wall
- Roof type and the size of any lantern or roof windows
- How much of the existing house is opened up
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 Hounslow?
Approvals for a single-storey extension in Hounslow follow the rules for 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.
Our first visit includes a check of your planning history, so you know the route before paying for drawings.
What we handle
From survey to sign-off, the job normally involves:
- Building control inspections and completion certificate
- Measured survey and design drawings
- Doors, windows and roof glazing installed
- Knock-through to the existing house with steel beams
- Structural calculations for steels and lintels
- Cavity walls, insulation and roof to current building regulations
How long does it take?
Expect 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 Hounslow
Space is at a premium in London, so homeowners often build out into the side return or up into the roof rather than move.
Hounslow sits in Greater London, about 12 miles west of central London. We cover the whole of Hounslow, including postcodes TW3, TW4 and TW6.
How it works
- 01
Survey and brief
We visit, discuss your ideas and budget, and survey the property or site at no cost.
- 02
Design and fixed quote
Drawings, structural calculations and an itemised, fixed price for the agreed specification.
- 03
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about single-storey extensions in Hounslow
How long does a single-storey extension take in Hounslow?
Typically 10 to 14 weeks on site for a typical rear extension, after approvals. Design and approvals beforehand usually take 6 to 12 weeks.
Do I need a party wall agreement?
If you are in England or Wales and the work involves a shared wall, building on the boundary or digging foundations close to a neighbour, the Party Wall etc. Act 1996 applies and notices must be served before work starts. We advise on this at the design stage.
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 much does a single-storey extension cost in Hounslow?
In Hounslow, 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.
What is a build-over agreement?
If a public sewer runs within 3 metres of the extension, the water company normally has to agree to the work before it starts. We check sewer records during design and apply where needed.