Knowle, West Midlands
Semi-detached rear extension in Knowle
Thinking about a semi-detached rear extension in Knowle? Single or two-storey extensions for semi-detached houses, with side access and one party wall. Our team handles the drawings, the planning route and the build, and your contract is with one company throughout.
Knowle sits in the West Midlands, with postcode districts including B40. In Knowle 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 Knowle?
Guide prices for a semi-detached rear extension in Knowle start from our West Midlands rate of £1,900–£3,100 per square metre, including VAT. The West Midlands is the baseline for our guide prices.
| Size | Guide price inc VAT |
|---|---|
| 3 m wide × 4 m deep (12 m²) | £23,000–£37,000 |
| 4 m wide × 5 m deep (20 m²) | £38,000–£62,000 |
| 4 m wide × 6 m deep (24 m²) | £45,500–£74,500 |
These are guide ranges; the written quote after the survey is the figure that counts.
Do you need planning permission for a semi-detached rear extension in Knowle?
Planning for a semi-detached rear extension in Knowle 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.
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.
If 3 or 4 metres is not enough, England's prior approval route allows 6 metres on a terraced or semi-detached house and 8 metres on a detached house for a single-storey rear extension. Neighbours are consulted, the council decides within 42 days, and the fee is £249, rising to £310 from 8 December 2026.
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 Knowle like to extend?
Red-brick terraces and 1930s semis make up much of Knowle. Many already have a small kitchen lean-to at the back, which a new rear extension usually replaces rather than adds to.
How a semi-detached rear extension in Knowle comes together
Free site visit
We measure the house and garden, look at the back wall, drainage and boundaries, and talk through what you want from the space.
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.
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 Knowle
Neighbouring places we cover include Solihull (2.9 miles) and Shirley (4.1 miles).
- Semi-detached rear extension in Solihull
- Semi-detached rear extension in Shirley
- Semi-detached rear extension in Acocks Green
- Semi-detached rear extension in Chelmsley Wood
- Semi-detached rear extension in Kenilworth
Other work in Knowle:
FAQ
Semi-detached rear extension questions in Knowle
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.
Who will build my extension?
Vetted building teams working under contract to us. Your contract is with S&K Property Investments and Improvement Ltd for the design and the build.
How long does a semi extension take?
10 to 16 weeks on site for a single-storey extension.
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 you match the brick or stone on my Knowle house?
We source the closest match and show you samples before ordering; reclaimed materials are often the best match on older houses.
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.