Trowbridge, Wiltshire
Semi-detached rear extension in Trowbridge
We plan and build rear extensions for semi-detached houses for homeowners in Trowbridge. Single or two-storey extensions for semi-detached houses, with side access and one party wall. Start with a free site visit, then a written price once the design is agreed.
Trowbridge sits in Wiltshire, with postcode districts including BA14. In Trowbridge 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 Trowbridge?
For Trowbridge we work from the South West England rate: £1,980–£3,220 per square metre of new floor, including VAT, 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 |
Your written price follows a measured survey and an agreed design, so it reflects your house, not an average.
Do you need planning permission for a semi-detached rear extension in Trowbridge?
Here is how the rules in England apply to a semi-detached rear extension in Trowbridge.
Under England's householder permitted development rules you can usually add 3 metres at the back of an attached house, or 4 metres on a detached house, without a planning application, as long as the extension stays under 4 metres high and its eaves stay under 3 metres where it is within 2 metres of a boundary.
A two-storey rear extension can be permitted development in England only if it projects no more than 3 metres, stays at least 7 metres from the rear boundary, matches the existing roof pitch and has obscure-glazed upper side windows. In practice most double-storey rear extensions go through a householder planning application.
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. At the first visit we measure what is there now and tell you which route fits: permitted development, prior approval or a planning application.
What are homes in Trowbridge like to extend?
Stone-built and rendered houses are common around Trowbridge, so matching the walling is a design decision in its own right: natural stone, reconstituted stone or a render finish across old and new.
How a semi-detached rear extension in Trowbridge comes together
Survey visit
We visit free of charge, measure up, check access, drainage and neighbours' extensions, and note what you want the room to do.
Drawings and budget
Floor plans and elevations for the options, each with a guide price.
Planning and regulations
We take the design through the right planning route, then produce the construction drawings and engineer's calculations for building control.
Build and sign-off
We build to the approved drawings with regular updates, then hand over the building control completion certificate and any guarantees from suppliers.
Semi-detached rear extensions near Trowbridge
Neighbouring places we cover include Westbury (4.2 miles) and Melksham (4.8 miles).
- Semi-detached rear extension in Westbury
- Semi-detached rear extension in Melksham
- Semi-detached rear extension in Neston
- Semi-detached rear extension in Bath
- Semi-detached rear extension in Frome
Other work in Trowbridge:
FAQ
Semi-detached rear extension questions in Trowbridge
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.
Do I need planning permission for a rear extension in Trowbridge?
Often not for a single-storey rear extension of up to 3 metres (4 metres on a detached house) under permitted development, or up to 6 or 8 metres with prior approval, unless the house is in a conservation area or its rights have been removed.
Single or two-storey on a semi?
Two-storey if you need bedrooms, single-storey if you need a bigger kitchen. Planning risk is lower for single-storey.
Will I need a structural engineer?
Yes for the beam over the new opening and usually the foundations; we arrange them and their calculations go to building control.
Can you match the brick or stone on my Trowbridge house?
We source the closest match and show you samples before ordering; reclaimed materials are often the best match on older houses.
Is the site visit in Trowbridge free?
Yes. We visit, measure up and talk through the options with no cost and no obligation.