Thornbury side return extensions, designed and built
If you live in Thornbury and want more space without moving, a side return extension is one of the most practical ways to get it. We handle the drawings, approvals and the build.
- Guide price in ThornburyFrom £18,000 inc VAT
- PlanningOften permitted development; party wall notice usual
- Build time10–14 weeks on site
- Postcode districtsBS35
Local to Thornbury
Postcode districts we cover around Thornbury include 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.
What is included
- Removal of the side wall and new steelwork
- Party wall notice support (England and Wales)
- Kitchen-ready shell or full finish
- Glazed, sloping or flat roof with rooflights
- New boundary wall or raised party wall
- Design to keep daylight in the middle of the house
Light is the design problem. A side return can make the middle of the house darker if the roof is solid, so we model the daylight and usually recommend a glazed slope or a run of rooflights along the boundary edge.
What should I budget for a side return extension in Thornbury?
Prices below are for Thornbury, using the South West England factor of ×1.02. They are guide ranges including VAT for the build only, not a quote.
Typical rates in Thornbury: £2,140 to £3,880 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| 1.8 m × 4.5 m 8 m² | £18,000 – £22,000 | £19,500 – £24,500 | £24,000 – £31,500 |
| 2 m × 5.5 m 11 m² | £23,500 – £28,500 | £26,500 – £34,000 | £33,500 – £43,000 |
| 2.2 m × 7 m 15 m² | £32,000 – £38,500 | £36,500 – £46,000 | £45,500 – £58,500 |
For a figure based on your own dimensions, use our guide-price tool.
Will the council need to approve it?
In England a single-storey side return infill is often permitted development if it stays within the height limits and is no wider than half the width of the original house. Conservation areas, listed buildings and flats always need an application, and the boundary wall usually brings in the Party Wall Act.
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 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.
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).
From first visit to completion
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
It starts with a visit to your house to measure, check access and talk through ideas and budget.
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
We confirm the build price in writing, based on the approved drawings and the finishes you have chosen.
Build and sign-off
Our team builds the extension, keeps you updated weekly and finishes with building control sign-off.
Side return extension questions answered
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.
Do I need building regulations approval in Thornbury?
Yes. Almost every extension needs it, whatever the planning route. We prepare the drawings and book the inspections.
Do you cover all of Thornbury?
Yes. We cover Thornbury and the surrounding parts of Gloucestershire. Site visits are free and there is no obligation.
How much does a side return extension cost?
Our guide range is about £2,140 to £3,880 per m² including VAT, so a typical 2 m × 5.5 m infill lands around £26,500 to £34,000 at standard spec in Thornbury, more in London.
Will the kitchen be darker?
Not if the roof is designed well. A glazed roof or a line of rooflights along the boundary usually makes the room brighter than before.
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.