Two-storey rear extensions in Chalfont Saint Peter
Want to stay in Chalfont Saint Peter but need more space? A two-storey rear extension adds floor area on two levels without giving up much garden. Here's what's involved.
The basics for Chalfont Saint Peter at a glance.
- Postcode districts
- HP8
- County / area
- Buckinghamshire, England
- Price region
- South East England
- Guide price
- £61,500–£83,000 (£2,200–£2,970 per m²)
- Approval route
- It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission.
- Nearest towns
- Gerrards Cross (1.6 miles), Chorleywood (3.6 miles), Beaconsfield (3.9 miles)
- Distance to Milton Keynes
- about 31.1 miles
- First visit
- Free, no obligation
About a two-storey rear extension
A two-storey rear extension is a new two-floor addition built onto the back of your house, usually giving a larger kitchen or living space on the ground floor and one or two bedrooms or a bathroom above. Because both floors share one set of foundations and one roof, it adds a lot of floor space for the garden it uses. In some cases it can be built under permitted development, depending on where you live.
We cover Chalfont Saint Peter (HP8) and the places around it, including Gerrards Cross (1.6 miles), Chorleywood (3.6 miles) and Beaconsfield.
What it costs in Chalfont Saint Peter
Our guide for South East England is £2,200–£2,970 per m² including VAT. On a project with a 4 m × 3.5 m footprint on two floors (28 m² of new floor space), that puts a two-storey rear extension in Chalfont Saint Peter at roughly £61,500–£83,000. We'll give you a written design-stage price first, then a fixed build price once the drawings are agreed.
| Spec | Per m² | A 4 m × 3.5 m footprint on two floors (28 m² of new floor space) |
|---|---|---|
| Essential | £2,020–£2,730 per m² | £56,500–£76,500 |
| Standard | £2,200–£2,970 per m² | £61,500–£83,000 |
| Premium | £2,640–£3,560 per m² | £74,000–£100,000 |
Planning and building regulations in Chalfont Saint Peter
In England, a two-storey rear extension can be permitted development if it goes no more than 3 m beyond the rear wall of the original house, stays at least 7 m from the rear boundary and matches the house's materials and roof pitch. It is not permitted development in conservation areas, National Landscapes, National Parks, World Heritage Sites or the Broads. Otherwise a householder application costs £548 (or £575 for applications made from 8 December 2026).
Approval in England: Householder planning application: £548 (or £575 for applications made from 8 December 2026). Lawful development certificate: £274 (about £288 for applications from 8 December 2026). Councils should decide householder applications within 8 weeks of validation.
Building regulations: Building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end.
Design points for Chalfont Saint Peter homes
Upstairs layout and windows
Bedrooms above need a window big enough for escape or a protected route to the stairs. Side-facing upstairs windows normally have to be obscure-glazed and fixed below 1.7 m, so we put the main bedroom windows in the rear wall and use roof lights where extra daylight is needed.
Opening up the ground floor
Knocking through the old rear wall means steel beams to carry the first floor and roof above. The structural engineer sets the beam sizes, padstones and any posts, and we plan them early so the open-plan layout you want is the one that gets built.
How we'd run your project
Free site visit
We visit your home in Chalfont Saint Peter, look at the structure, access and boundaries, and talk through what you want the new rooms to do.
Drawings and permission
Our designers produce plans and elevations, then we take care of planning or permitted development checks with the council covering Chalfont Saint Peter.
Engineer it
Foundations sized for two floors, steels for any openings, and building control approval, all before anyone starts on site.
Finish and certify
Second fix, plastering and making good, then building control's final inspection and the completion paperwork.
Questions about two-storey rear extensions in Chalfont Saint Peter
Do I need planning permission for a two-storey rear extension in Chalfont Saint Peter?
Chalfont Saint Peter is in England, so England planning rules apply. It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.
How much does a two-storey rear extension cost in Chalfont Saint Peter?
Our guide for South East England, which covers Chalfont Saint Peter, is £2,200–£2,970 per m² including VAT. A typical project with a 4 m × 3.5 m footprint on two floors (28 m² of new floor space) comes to about £61,500–£83,000. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.
Who handles building regulations for a project in Chalfont Saint Peter?
We handle it as part of the project. What's needed in England: building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end. We prepare the drawings and the engineer's calculations, book the inspections and pass you the completion paperwork at the end.
Will a two-storey rear extension block my neighbour's light?
It can if it is too deep or too close to the boundary, which is why councils look closely at its effect on neighbouring windows and gardens. We test the design against light and outlook early, keep the first floor shorter or set in where needed, and use a hipped roof to reduce bulk on the boundary side.
Can I have a balcony on a two-storey rear extension?
In England, balconies, verandas and raised platforms are not permitted development, so a balcony on a two-storey rear extension needs planning permission. A Juliet balcony, a guard rail across full-height doors with no platform to stand on, is often a practical alternative, but it still needs checking against the rules and the council's approach to overlooking.
Nearby
Nearby towns we cover for two-storey rear extensions:
Other extensions in Chalfont Saint Peter
- Side
- Wraparound
- Part two-storey
- Over a garage
- First floor
- Semi-detached
- Detached
- Kitchen and bedrooms
- Bedroom and en-suite
All two-storey extension services in Chalfont Saint Peter · Two-storey rear extensions across Buckinghamshire
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