Extensions in Cornwall: design, planning and build
Looking to extend your home in Cornwall? Start here: extension types, guide prices for Cornwall, the planning rules that apply and how a project runs.
- Towns listed9
- Price regionSouth West England (×1.02)
- Planning rulesEngland
- Postcode districts50
Towns we cover in Cornwall
Towns we cover here include Redruth, Falmouth, St Austell, Truro.
Planning and building control in Cornwall
In England a single-storey rear extension can usually go up to 3 m beyond the original rear wall of a semi-detached or terraced house, or 4 m on a detached house, without a planning application, provided it is no more than 4 m high, keeps eaves to 3 m within 2 m of a boundary and, with other buildings, covers no more than half the land around the original house. The larger home extension prior approval scheme raises those depths to 6 m and 8 m, with neighbours notified and a 42-day decision.
In a conservation area, national park, National Landscape, the Broads or a World Heritage Site the permitted development limits are tighter (no side or two-storey extensions without an application). Listed homes need listed building consent, and if permitted development rights have been removed, any extension needs an application.
Building regulations approval is separate from planning. In England you can use the council's building control team or a registered building control approver; a full plans application gets the drawings checked before work starts, and the inspector signs the work off with a completion certificate.
Cornwall extension prices at a glance
Use these Cornwall guide prices to sense-check a budget; the guide-price tool narrows them to your own size, and the site visit turns them into a written figure.
| Extension type | Example size | Standard spec (inc VAT) |
|---|---|---|
| Single-storey rear extensions | 20 m² | £41,500 – £53,500 |
| Orangery extensions | 16 m² | £45,500 – £57,500 |
| Wraparound extensions | 25 m² | £58,500 – £74,000 |
| Conservatory replacement extensions | 14 m² | £30,500 – £39,500 |
| Kitchen extensions | 20 m² | £42,500 – £54,500 |
| Side return extensions | 11 m² | £26,500 – £34,000 |
| Double-storey extensions | 32 m² | £58,500 – £77,000 |
What works best for Cornwall houses?
South West homes range from terraced streets in the cities to stone cottages and bungalows in the countryside, and conservation areas are common in historic centres.
Depending on the plot, annexe extensions and orangery extensions are often the strongest options, with pitched roof extensions worth considering where there is room.
Choose an extension type
- Wraparound extensions · from £36,500
- Side extensions · from £22,000
- Kitchen extensions · from £27,500
- Conservatory replacement extensions · from £20,000
- Extension plans and drawings · from £1,200
- Annexe extensions · from £56,000
- Home office extensions · from £16,000
- Single-storey rear extensions · from £21,000
- Building regulations for extensions · from £900
- Flat roof extensions · from £21,000
- Side return extensions · from £18,000
- Planning permission for extensions · from £350
- Timber frame extensions · from £21,000
- Porch extensions · from £4,050
- Bedroom extensions · from £26,500
- Extensions over a garage · from £24,000
- Bungalow extensions · from £26,500
- Double-storey extensions · from £38,500
- Glass box extensions · from £30,500
- Orangery extensions · from £30,500
- Pitched roof extensions · from £22,500
- Utility and boot room extensions · from £14,000
Questions about extensions in Cornwall
How much does an extension cost in Cornwall?
With our South West England factor (×1.02), a standard-spec 20 m² single-storey extension is a guide £41,500 to £53,500 including VAT. Prices for every type are linked on this page.
Will my neighbours need to be told?
If you apply for planning or prior approval the council notifies them, and in England party wall notices may be needed for work near a shared boundary.
Do you cover all of Cornwall?
Yes, across the whole of Cornwall. Site visits are free and there is no obligation.
How long does an extension take in Cornwall?
Usually 2 to 4 months of design and approvals, then 10 to 16 weeks on site for a single-storey extension or 16 to 24 weeks for two storeys.
Book a free site visit in Cornwall
We will measure up, check the planning position and give you honest guide figures.
- Free, no-obligation site visit
- Planning route checked before you spend on drawings
- Written price once the design is agreed
- Building control sign-off at the end
Prefer to talk? Call 0800 088 6341 or .
Book a free site visit
Tell us a little about the project and we will arrange a time.