Double-storey extensions in High Wycombe
From the first sketch to final sign-off, we plan and build double-storey extensions in High Wycombe and the surrounding Buckinghamshire area.
- Guide price in High WycombeFrom £42,500 inc VAT
- PlanningUsually a householder application
- Build time16–24 weeks on site
- Postcode districtsHP10, HP11, HP12, HP13, HP14
Extensions in and around High Wycombe
Postcode districts we cover around High Wycombe include HP10, HP11, HP12, HP13, HP14, HP15. Nearby, we also take on projects in Marlow (4 miles), Amersham (6 miles), Chesham (8 miles), Chalfont St Peter (8 miles).
Just over the Berkshire border, Maidenhead is about 7 miles away. In the South East, plenty of houses have already been extended once, which makes checking the remaining permitted development allowance an important early step.
Is a double-storey extension right for your house?
- Houses with enough distance to the rear or side boundary
- Growing families who need a bedroom as well as a bigger kitchen
- Homeowners who would otherwise consider moving
The roof is what makes a two-storey extension look right or wrong. We match the pitch and materials of the main house wherever possible and plan the upstairs layout around the existing landing so the new rooms feel original rather than bolted on.
Planning and approvals in High Wycombe
In England a two-storey rear extension is permitted development only if it projects no more than 3 m from the original rear wall, sits at least 7 m from the rear boundary, matches the roof pitch and uses obscure, non-opening side windows upstairs. Most two-storey extensions therefore go through a householder planning application, which costs £548 from 1 April 2026 and normally takes about 8 weeks.
The planning position for a specific High Wycombe address depends on its history and any designations, which is why we check it at the first visit.
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 regulations approval is separate from planning. In England you can use the council's building control team or a registered building control approver; a full plans application gets the drawings checked before work starts, and the inspector signs the work off with a completion certificate.
Applications are decided by the local planning authority (your district, borough or unitary council).
How much does a double-storey extension cost in High Wycombe?
For High Wycombe we adjust our national guide rates by ×1.12, the factor we use for South East England. Figures include VAT; your written quote after the survey replaces them.
Typical rates in High Wycombe: £1,740 to £3,360 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| 3 m × 4 m, two floors 24 m² | £42,500 – £51,000 | £48,000 – £63,500 | £61,500 – £81,000 |
| 4 m × 4 m, two floors 32 m² | £55,500 – £66,500 | £64,500 – £84,500 | £82,000 – £108,000 |
| 4 m × 6 m, two floors 48 m² | £83,000 – £99,500 | £96,500 – £126,500 | £123,500 – £161,500 |
For a figure based on your own dimensions, use our guide-price tool.
How the project works
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
We draw the design, agree it with you and handle planning or permitted development checks and building regulations.
Fixed written price
You receive a written, itemised price and programme. Nothing starts until you are happy with it.
Build and sign-off
Work is carried out to the agreed programme, inspected by building control and signed off at the end.
Questions people ask about double-storey extensions
Do I need building regulations approval in High Wycombe?
Yes. Almost every extension needs it, whatever the planning route. We prepare the drawings and book the inspections.
How long does a double-storey extension take to build in High Wycombe?
On site, typically 16 to 24 weeks once approvals are in place. Before that, allow 8–16 weeks design and approvals.
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.
Do I need a Party Wall Agreement?
If you are in England or Wales and the work involves a shared wall or digging foundations close to a neighbour, the Party Wall etc. Act 1996 applies and notices must be served before work starts. We tell you which notices are needed.
Does a double-storey extension need planning permission?
Often, yes. In England a two-storey rear extension can be permitted development only if it projects no more than 3 m and sits at least 7 m from the rear boundary, with matching roof pitch and obscure side windows. Side extensions over one storey always need planning permission. We confirm the route at the survey.
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.