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 Watford?
In Watford, a single-storey extension typically costs £2,050–£3,050 per m² of floor area, including VAT at 20% (standard rate). For a typical 20 m² project that is roughly £41,000–£61,000. The guide for Watford reflects typical costs in the East of England, roughly 6% above the UK-wide figure. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (14 m²) | £28,500–£42,500 |
| Typical project (20 m²) | £41,000–£61,000 |
| Larger project (28 m²) | £57,500–£85,500 |
| Rate per m² | £2,050–£3,050 |
The main things that change the cost:
- Roof type and the size of any lantern or roof windows
- Ground conditions and foundation depth
- How much of the existing house is opened up
- 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 Watford?
The approval route for Watford 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.
Building regulations approval comes from the council’s building control service or a registered building control approver. The work is inspected at key stages, such as foundations, drainage and insulation, and a completion certificate is issued at the end.
If the answer is not clear-cut, we can apply for formal confirmation before you commit to the build.
What we handle
What we take care of:
- Doors, windows and roof glazing installed
- Knock-through to the existing house with steel beams
- Cavity walls, insulation and roof to current building regulations
- Structural calculations for steels and lintels
- First and second fix electrics, heating and plastering
- 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 Watford
Across the East of England, 1930s and post-war semis, newer estates and rural cottages all feature, each with different extension and loft options.
Our Watford coverage includes postcode districts WD1, WD17, WD18 and WD19, and we also work in nearby places such as Bushey, North Watford and Rickmansworth.
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
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 Watford
Who approves a single-storey extension in Watford?
Planning matters in Watford go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.
How long does a single-storey extension take?
Once approvals are in place, a typical rear extension takes 10 to 14 weeks on site. Design and approvals usually take another 6 to 12 weeks beforehand, depending on whether a planning application is needed.
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.
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.
How much does a single-storey extension cost in Watford?
In Watford, a single-storey extension typically costs £2,050–£3,050 per m² of floor area, including VAT at 20% (standard rate). A typical 20 m² project comes to roughly £41,000–£61,000. Your fixed price depends on the survey and drawings.