House extensions in Dorchester
Planning an extension in Dorchester? Compare extension types, see guide prices adjusted for Dorchester and book a free site visit.
- Postcode districtsDT1
- Price regionSouth West England (×1.02)
- Planning rulesEngland
- Site visitFree, no obligation
Where we work near Dorchester
Postcode districts we cover around Dorchester include DT1. Nearby, we also take on projects in Weymouth (7 miles), Bridport (15 miles), Poole (20 miles), Wimborne Minster (22 miles), Swanage (22 miles). For homes towards Somerset, Yeovil is around 18 miles away.
Popular extension prices in Dorchester
Every figure below is a guide for Dorchester, adjusted for South West England build costs (×1.02) and including VAT. Design and council fees are shown separately on each page.
| Extension type | Example size | Standard spec (inc VAT) |
|---|---|---|
| Single-storey rear extensions | 20 m² | £41,500 – £53,500 |
| Side return extensions | 11 m² | £26,500 – £34,000 |
| Orangery extensions | 16 m² | £45,500 – £57,500 |
| Double-storey extensions | 32 m² | £58,500 – £77,000 |
| Wraparound extensions | 25 m² | £58,500 – £74,000 |
Which extension suits a Dorchester home?
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, single-storey rear extensions and annexe extensions are often the strongest options, with pitched roof extensions worth considering where there is room.
Planning rules in Dorchester
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 England a two-storey rear extension is permitted development only if it projects no more than 3 m from the original rear wall, sits at least 7 m from the rear boundary, matches the roof pitch and uses obscure, non-opening side windows upstairs. Most two-storey extensions therefore go through a householder planning application, which costs £548 from 1 April 2026 and normally takes about 8 weeks.
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.
Applications are decided by the local planning authority (your district, borough or unitary council).
Choose an extension type
- Utility and boot room extensions · from £14,000
- Conservatory replacement extensions · from £20,000
- Flat roof extensions · from £21,000
- Annexe extensions · from £56,000
- Home office extensions · from £16,000
- Bungalow extensions · from £26,500
- Bedroom extensions · from £26,500
- Side return extensions · from £18,000
- Single-storey rear extensions · from £21,000
- Extensions over a garage · from £24,000
- Extension plans and drawings · from £1,200
- Double-storey extensions · from £38,500
- Pitched roof extensions · from £22,500
- Glass box extensions · from £30,500
- Timber frame extensions · from £21,000
- Orangery extensions · from £30,500
- Porch extensions · from £4,050
- Planning permission for extensions · from £350
- Side extensions · from £22,000
- Kitchen extensions · from £27,500
- Building regulations for extensions · from £900
- Wraparound extensions · from £36,500
Free site visit
First, a site visit: we look at the house, garden, access and drains and listen to what you need.
Design and approvals
Drawings are prepared and agreed with you, then submitted for the right planning route and building regulations approval.
Fixed written price
You receive a written, itemised price and programme. Nothing starts until you are happy with it.
Build and sign-off
We build it with one project manager, book the building control inspections and hand over the completion certificate.
Questions about extensions in Dorchester
How much does an extension cost in Dorchester?
Using our South West England factor (×1.02), a standard-spec single-storey extension of 20 m² is a guide £41,500 to £53,500 including VAT, and a 32 m² two-storey extension £58,500 to £77,000. Your written price follows the survey.
How long does an extension take in Dorchester?
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.
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 handle building regulations?
Yes. We prepare the drawings and calculations, submit them and book inspections, ending with a completion certificate.
Book a free site visit in Dorchester
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.