Keynsham, Somerset
Semi-detached rear extension in Keynsham
Semi-detached rear extension in Keynsham: single or two-storey extensions for semi-detached houses, with side access and one party wall. We measure the house, show you what the rules allow, price it in writing and build it.
Keynsham is covered from our Somerset round, including BS31. In Keynsham we measure the attached neighbour's extension at the survey, because it often sets the sensible depth for yours.
Book a free site visit
Tell us about the house and we'll call to arrange a free, no-obligation visit.
How much does a semi-detached rear extension cost in Keynsham?
In Keynsham, our guide for a semi-detached rear extension is £1,980–£3,220 per square metre including VAT for a standard specification. South West prices run slightly above our West Midlands baseline; natural stone to match the house is the main variable.
| Size | Guide price inc VAT |
|---|---|
| 3 m wide × 4 m deep (12 m²) | £23,500–£38,500 |
| 4 m wide × 5 m deep (20 m²) | £39,500–£64,500 |
| 4 m wide × 6 m deep (24 m²) | £47,500–£77,500 |
We put a fixed price in writing once the design is agreed, and explain any provisional sums such as foundations.
Do you need planning permission for a semi-detached rear extension in Keynsham?
Planning for a semi-detached rear extension in Keynsham follows the English householder rules.
In England a single-storey rear extension can often be built under permitted development: up to 3 metres beyond the original rear wall of an attached house, or 4 metres on a detached house, no higher than 4 metres, with eaves no higher than 3 metres if any part is within 2 metres of a boundary.
England's rules allow a rear extension of more than one storey without an application only when it is no deeper than 3 metres and at least 7 metres from the boundary opposite the rear wall, and never on designated land. Most two-storey schemes need householder planning permission.
England also has the larger home extension route: a single-storey rear extension of up to 6 metres on an attached house or 8 metres on a detached house, after prior approval from the council. The council notifies your neighbours and has 42 days to decide; the fee is £249 (£310 for applications made from 8 December 2026). The route is not available on designated land such as conservation areas.
Conservation areas, National Parks, National Landscapes and the Broads restrict permitted development, and listed buildings always need listed building consent. Before any drawing we look up the property's history with the council, because earlier extensions and removed rights change the answer.
What are homes in Keynsham like to extend?
Keynsham has Victorian terraces nearer the centre and post-war semis on the edges. Sloping gardens are frequent, which affects floor levels and steps down to the patio.
How a semi-detached rear extension in Keynsham comes together
Look round and measure
A free visit to see the back of the house, measure it, check the drains and boundaries and hear what you need.
Drawings and budget
Floor plans and elevations for the options, each with a guide price.
Paperwork handled
Planning, prior approval or permitted development, Building Regulations approval, structural design and party wall notices are all handled by us.
Written price, then build
Once the design and approvals are in place, you get a fixed written price and programme, and we build through to sign-off.
Semi-detached rear extensions near Keynsham
Close by, we work in Kingswood, about 2.7 miles away, and Mangotsfield, about 5.1 miles away.
- Semi-detached rear extension in Kingswood
- Semi-detached rear extension in Mangotsfield
- Semi-detached rear extension in Bristol
- Semi-detached rear extension in Bishopsworth
- Semi-detached rear extension in Bath
Other work in Keynsham:
FAQ
Semi-detached rear extension questions in Keynsham
Do I need a party wall agreement?
In England, usually yes if the extension is on or near a shared boundary or the foundations are close to a neighbour's building. We serve the notices.
Can I live at home while the extension is built?
Usually yes. Most of the work is outside until the back wall is opened near the end, and that stage is screened off.
How long does a semi extension take?
10 to 16 weeks on site for a single-storey extension.
Is the site visit in Keynsham free?
Yes. We visit, measure up and talk through the options with no cost and no obligation.
Do you handle building control in Keynsham?
Yes. We apply to the council or a registered building control approver and hand over the completion certificate.
Can you match the brick or stone on my Keynsham house?
We source the closest match and show you samples before ordering; reclaimed materials are often the best match on older houses.