Side extensions in Thornbury: design, approvals and build
Planning a side extension in Thornbury? We survey the house, work out the planning route, draw the design and build it, so you deal with one team from the first visit to the completion certificate.
- Guide price in ThornburyFrom £22,000 inc VAT
- PlanningSingle storey can be permitted development
- Build time10–18 weeks on site
- Postcode districtsBS35
Working in Thornbury
Site visits are available across Thornbury (BS35). The same team covers Yate (7 miles), Mangotsfield (8 miles), Kingswood (10 miles), Dursley (10 miles), all within easy reach.
For homes towards Somerset, Portishead is around 12 miles away. 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.
Planning and approvals in Thornbury
In England a single-storey side extension can be permitted development if it is no more than 4 m high and no wider than half the width of the original house. Two-storey side extensions, and any side extension on designated land such as a conservation area, need a householder planning application.
Before any drawing is finalised we check whether the house is listed, in a conservation area or subject to an Article 4 direction.
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.
Building over or within 3 m of a public sewer needs the water company's consent, usually through a build-over agreement, before the foundations go in.
Applications are decided by the local planning authority (your district, borough or unitary council).
Guide prices for Thornbury
For Thornbury we adjust our national guide rates by ×1.02, the factor we use for South West England. Figures include VAT; your written quote after the survey replaces them.
Typical rates in Thornbury: £1,780 to £3,470 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| 2.5 m × 5 m 12 m² | £22,000 – £27,000 | £25,000 – £32,500 | £31,500 – £42,000 |
| 3 m × 6 m 18 m² | £32,000 – £39,000 | £37,500 – £49,000 | £47,500 – £62,500 |
| 3 m × 8 m 24 m² | £42,500 – £51,500 | £50,000 – £65,000 | £63,500 – £83,500 |
Try the guide-price tool to see a range for your own size and finish.
Included in a typical project
- Structure, roof tied into the house
- Windows, doors and finishes to match
- Foundations near boundaries and any drains
- New openings through the side wall
- Survey, design and street-view drawings
- Planning route checked or application made
What happens next
Site visits are free and there is no obligation. Where drawings are needed, the design stage is priced in writing before it starts.
Free site visit
A designer visits, takes measurements and photos, and discusses layouts, budget and timing with you.
Design and approvals
Once the layout is agreed, we deal with the council: planning permission or written confirmation that none is needed, plus building control.
Fixed written price
You receive a written, itemised price and programme. Nothing starts until you are happy with it.
Build and sign-off
The build is managed from start to finish, inspected at each stage and signed off on completion.
Questions people ask about side extensions
Can I see a price before committing to anything?
Yes. The guide prices on this page are adjusted for Thornbury, and the guide-price tool gives a range for your own size. After the survey you get a written price before anything is agreed.
Who do I contract with for a side extension in Thornbury?
Your contract is with S&K Property Investments and Improvement Ltd, which designs and manages the project and the build teams who carry it out.
How long does a side extension take to build in Thornbury?
On site, typically 10 to 18 weeks once approvals are in place. Before that, allow 6–14 weeks design and approvals.
How much does a side extension cost?
Our guide range is about £1,780 to £3,470 per m² including VAT, depending on specification, so a standard 18 m² single-storey side extension lands around £37,500 to £49,000 in Thornbury.
How close to the boundary can I build?
It depends on height. In England, within 2 m of a boundary the eaves must not exceed 3 m under permitted development. Building on the boundary is possible but brings party wall and maintenance access issues we plan for.
Book a free site visit in Thornbury
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.