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 Cambridgeshire?
In Cambridgeshire, 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. Building costs in the East of England run about 6% above the UK average, and the figures for Cambridgeshire are adjusted to reflect that. 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
- How much of the existing house is opened up
- Ground conditions and foundation depth
- Floor area and the length of new wall
A guide range is only a starting point: the guide price tool gives an instant figure for your size, and a free survey turns it into a fixed quote.
Do you need planning permission for a single-storey extension in Cambridgeshire?
Whether you need planning permission depends on your house and its location 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
On a typical single-storey extension we handle:
- Knock-through to the existing house with steel beams
- Building control inspections and completion certificate
- Foundations, drainage and any build-over agreement
- Measured survey and design drawings
- First and second fix electrics, heating and plastering
- 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. Before that, surveys, drawings and approvals usually take 6 to 12 weeks, longer if the council asks for changes.
Building in Cambridgeshire
Many towns in the East of England have estates built since the 1970s, where garage conversions and rear extensions are popular.
Towns we cover in Cambridgeshire include Peterborough, Cambridge, Wisbech, St Neots, Huntingdon and March.
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 pricing
Design options, then a fixed quote based on the chosen drawings and specification.
- 03
Approvals in place
We handle planning, building control and neighbour notices before work starts.
- 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 Cambridgeshire
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 Cambridgeshire?
In Cambridgeshire, 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.
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.
Who approves a single-storey extension in Cambridgeshire?
Planning matters in Cambridgeshire go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.