Annexe extensions in High Wycombe: design, approvals and build
A annexe extension in High Wycombe starts with the right design and the right approval route. We take care of both, then build it with our own project management.
- Guide price in High WycombeFrom £61,500 inc VAT
- PlanningUsually a householder application
- Build time16–24 weeks on site
- Postcode districtsHP10, HP11, HP12, HP13, HP14
Planning rules that apply in High Wycombe
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.
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.
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.
Applications are decided by the local planning authority (your district, borough or unitary council).
Covering High Wycombe
Our survey diary covers High Wycombe, including HP10, HP11, HP12, HP13, HP14, HP15. We also work in nearby Marlow (4 miles), Amersham (6 miles), Chesham (8 miles), Chalfont St Peter (8 miles).
In the South East, plenty of houses have already been extended once, which makes checking the remaining permitted development allowance an important early step.
What we take care of
- Fire separation and alarms to building regulations
- Design for accessibility: level thresholds, wider doors, walk-in shower
- Planning application describing ancillary use
- Separate or shared heating and hot water
- Kitchenette, shower room and bedroom finish
Annexe extension prices in High Wycombe
Labour and material costs vary across the UK, so for High Wycombe we use our South East England factor (×1.12). The ranges include VAT and exclude design, structural and council fees.
Typical rates in High Wycombe: £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 |
Try the guide-price tool to see a range for your own size and finish.
What happens next
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
We visit your High Wycombe home, measure up, talk through what you want and check the planning position.
Design and approvals
Drawings are prepared and agreed with you, then submitted for the right planning route and building regulations approval.
Fixed written price
You receive a written, itemised price and programme. Nothing starts until you are happy with it.
Build and sign-off
We build it with one project manager, book the building control inspections and hand over the completion certificate.
Annexe extension questions answered
Do you cover all of High Wycombe?
Yes. We cover High Wycombe and the surrounding parts of Buckinghamshire. Site visits are free and there is no obligation.
Who do I contract with for an annexe extension in High Wycombe?
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.
Will my neighbours in High Wycombe 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.
How much does an annexe extension cost?
Our guide range is about £2,240 to £4,260 per m² including VAT. A one-bedroom annexe of about 35 m² is typically £94,000 to £118,000 at standard spec in High Wycombe.
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 High Wycombe
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.