Two-storey side extensions in Buckinghamshire
If you're in Buckinghamshire and weighing up a two-storey side extension, start here: guide costs for South East England, the approvals you'll need and how we work.
Buckinghamshire at a glance
- Nation
- England
- Price region
- South East England
- Postcode areas
- HP, MK, SL
- Towns covered
- 13 listed below, plus surrounding villages
- Approval route
- Planning permission is needed: in England, permitted development only allows single-storey extensions to the side.
- Site visits
- Free, no obligation
What a two-storey side extension involves
A two-storey side extension is a new two-floor addition built into the space beside your house, often over a driveway or side passage. It typically adds one or two bedrooms upstairs and a utility, study or larger kitchen below, without giving up rear garden.
The main places we list in Buckinghamshire are Milton Keynes (MK5), High Wycombe (HP11), Aylesbury (HP17), Bletchley (MK1), Amersham (HP7) and Chesham (HP5). We cover the villages in between too.
Guide price in South East England
For budgeting in Buckinghamshire, allow around £94,500–£127,000 for a two-storey side extension with a 3 m × 7 m footprint on two floors (42 m² of new floor space). That's based on £2,260–£3,030 per m² including VAT for South East England. Professional fees for drawings and the structural engineer are listed separately on our prices page.
| Spec | Per m² | Typical project |
|---|---|---|
| Essential | £2,070–£2,780 per m² | £87,000–£117,000 |
| Standard | £2,260–£3,030 per m² | £94,500–£127,000 |
| Premium | £2,710–£3,630 per m² | £113,500–£152,500 |
Rules in England
In England, a two-storey side extension always needs householder planning permission, because permitted development only allows single-storey extensions beyond a side wall. The fee is £548 (or £575 for applications made from 8 December 2026), and councils should decide within 8 weeks of validation. Expect them to look at set-back, roof height, gaps to the boundary and the effect on neighbours.
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.
The Party Wall etc. Act 1996 applies, so notices may be needed for work on or near a shared wall or boundary.
Getting the design right
Avoiding a terracing effect
Where semi-detached houses sit close together, side extensions on neighbouring houses can join up and turn a row of pairs into a terrace. Many councils ask for a gap to the boundary at first floor to stop this, so we check local guidance before fixing the width.
Set-down and set-back
Councils usually want a two-storey side extension to look subordinate to the house. Setting the front wall back from the main front and dropping the ridge slightly below the main roof helps it read as an addition, and is often expected in local design guidance.
How we work in Buckinghamshire
Free site visit
We visit your home in Buckinghamshire, look at the structure, access and boundaries, and talk through what you want the new rooms to do.
Drawings, then consent
We draw the scheme, check it against the rules in England, and take it through the right consent with the council.
Detail and price
Construction drawings, engineer's calculations and building control sign-off, then a written fixed price for the build.
Build and hand over
We manage the build from groundworks to decoration-ready finish and hand over with the completion paperwork.
Towns we cover in Buckinghamshire
- Milton Keynes
- High Wycombe
- Aylesbury
- Bletchley
- Amersham
- Chesham
- Gerrards Cross
- Chalfont Saint Peter
- Marlow
- Amersham on the Hill
- Newport Pagnell
- Beaconsfield
- Buckingham
Two-storey side extensions in Buckinghamshire: questions
How much does a two-storey side extension cost in Buckinghamshire?
In South East England our guide is £2,260–£3,030 per m² including VAT, so about £94,500–£127,000 for a 3 m × 7 m footprint on two floors (42 m² of new floor space). Essential and Premium specs move that by roughly 8% down or 20% up.
Can I build a two-storey side extension over my driveway?
Yes, if the drive is wide enough for a useful room and the council accepts the design. You may lose off-road parking, which some councils weigh up, and the foundations need to suit the ground below. We check parking, drains and meter positions at the free site visit before any drawings are prepared.
Will I need planning permission in Buckinghamshire?
Buckinghamshire is in England. Planning permission is needed: in England, permitted development only allows single-storey extensions to the side.
Neighbouring areas
- Two-storey side extensions in Hertfordshire
- Two-storey side extensions in Bedfordshire
- Two-storey side extensions in Berkshire
- Two-storey side extensions in Oxfordshire
All extension services in Buckinghamshire · About two-storey side extensions
Ready to see what a second storey could do for your home?
Book a free site visit. We'll look at your house, talk through options and explain the approvals you'd need, then price the design stage in writing.