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 Crawley?
In Crawley, a single-storey extension typically costs £2,200–£3,250 per m² of floor area, including VAT at 20% (standard rate). For a typical 20 m² project that is roughly £44,000–£65,000. Building costs in the South East run about 12% above the UK average, and the figures for Crawley are adjusted to reflect that. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (14 m²) | £31,000–£45,500 |
| Typical project (20 m²) | £44,000–£65,000 |
| Larger project (28 m²) | £61,500–£91,000 |
| Rate per m² | £2,200–£3,250 |
Your quote will depend mainly on:
- Ground conditions and foundation depth
- Floor area and the length of new wall
- Roof type and the size of any lantern or roof windows
- Kitchen, flooring and finishes, which we can include or leave to you
Use the guide price tool to see how size and specification change the figure, then ask for a written, itemised quote.
Do you need planning permission for a single-storey extension in Crawley?
Approvals for a single-storey extension in Crawley 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
On a typical single-storey extension we handle:
- Building control inspections and completion certificate
- Foundations, drainage and any build-over agreement
- Knock-through to the existing house with steel beams
- Doors, windows and roof glazing installed
- Cavity walls, insulation and roof to current building regulations
- Measured survey and design drawings
How long does it take?
Allow 10 to 14 weeks on site for a typical rear extension, after approvals. Before that, surveys, drawings and approvals usually take 6 to 12 weeks, longer if the council asks for changes.
Building in Crawley
Commuter towns across the South East have many 1930s and post-war semis that suit rear extensions and hip-to-gable loft conversions.
Projects in Crawley (RH11 and RH77) are surveyed in person before we quote, so the price reflects your actual property.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 02
Design and pricing
Design options, then a fixed quote based on the chosen drawings and specification.
- 03
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Build and handover
Work follows the agreed programme, with inspections along the way and a completion certificate at the end.
Questions about single-storey extensions in Crawley
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 Crawley?
In Crawley, a single-storey extension typically costs £2,200–£3,250 per m² of floor area, including VAT at 20% (standard rate). A typical 20 m² project comes to roughly £44,000–£65,000. Your fixed price depends on the survey and drawings.
Do you build single-storey extensions in Crawley?
Yes. We build single-storey extensions across Crawley, including postcodes RH11 and RH77. Every project starts with a free home visit.
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.