Annexe extensions in Slough: design, approvals and build
From the first sketch to final sign-off, we plan and build annexe extensions in Slough and the surrounding Berkshire area.
- Guide price in SloughFrom £61,500 inc VAT
- PlanningUsually a householder application
- Build time16–24 weeks on site
- Postcode districtsSL1, SL2, SL3, SL4
What is included
- Fire separation and alarms to building regulations
- Separate or shared heating and hot water
- Design for accessibility: level thresholds, wider doors, walk-in shower
- Planning application describing ancillary use
- Kitchenette, shower room and bedroom finish
Accessibility is cheaper to design in than to retrofit. Level access, a 900 mm door width, a level-access shower and space to turn a wheelchair can all be planned into the footprint for little extra cost.
Do I need planning permission in Slough?
In England an annexe that stays part of the household and connects to the house is assessed as an extension, but its size usually takes it beyond permitted development, so a householder application describing the ancillary use is the normal route.
Homes in conservation areas, national parks, National Landscapes (formerly AONBs), the Broads and World Heritage Sites have tighter rules, so we always check the property's status and planning history before design starts.
If the work involves a shared wall, building on the boundary, or digging foundations within 3 m (sometimes 6 m) of a neighbour's building, the Party Wall etc. Act 1996 applies and notice must be served before work starts: two months for work to a party wall, one month for new walls on the boundary and for excavations.
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).
Annexe extension prices in Slough
Prices below are for Slough, using the South East England factor of ×1.12. They are guide ranges including VAT for the build only, not a quote.
Typical rates in Slough: £2,240 to £4,260 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| Studio annexe 25 m² | £61,500 – £77,500 | £67,000 – £84,500 | £84,000 – £106,500 |
| One-bedroom annexe 35 m² | £78,000 – £98,500 | £94,000 – £118,000 | £117,500 – £149,000 |
| Larger annexe 45 m² | £100,500 – £126,500 | £120,500 – £151,500 | £151,000 – £192,000 |
Want a range for your exact size? The guide-price tool takes about a minute.
Working in Slough
We cover Slough and the postcode districts SL1, SL2, SL3, SL4. Neighbouring towns we cover include Windsor (2 miles), Maidenhead (5 miles), Bracknell (9 miles), Wokingham (12 miles).
The South East has a broad mix of 1930s semis, post-war estates, newer developments and period cottages, and many houses have enough garden for a generous rear extension.
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.
Annexe extension questions answered
Will my neighbours in Slough be involved?
If a planning application or prior approval is needed, the council notifies neighbours. If the work is on or near a shared boundary, party wall notices may also be needed.
Who do I contract with for an annexe extension in Slough?
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.
Do you cover all of Slough?
Yes. We cover Slough and the surrounding parts of Berkshire. Site visits are free and there is no obligation.
Can the annexe have its own front door?
Yes, many do, but it should still connect to the main house to stay clearly part of it.
Will an annexe affect council tax?
It can. Some annexes are assessed separately for council tax, with discounts or exemptions in some cases when occupied by a relative. Check with the Valuation Office Agency (England and Wales), your local assessor (Scotland) or Land & Property Services (Northern Ireland).
Book a free site visit in Slough
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.