First-floor extensions in Oxford
Our first-floor extensions service in Oxford covers everything: measured survey, design, planning or permitted development checks, structural design, building control and the build itself.
What we'd confirm first for a project in Oxford.
- Postcode districts
- OX1, OX2 and OX3
- County / area
- Oxfordshire, England
- Price region
- South East England
- Guide price
- £27,500–£40,000 (£1,980–£2,860 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
- Cowley (2.5 miles), Kidlington (5 miles), Abingdon (5.7 miles)
- First visit
- Free, no obligation
About a first-floor extension
A first-floor extension is a new upstairs room built on top of an existing single-storey part of your house, such as a rear kitchen extension, a utility or a side annexe. It adds a bedroom, bathroom or study without enlarging the footprint. Whether it works depends mainly on whether the walls and foundations below can carry the extra load.
We cover Oxford (OX1, OX2 and OX3) and the places around it, including Cowley (2.5 miles), Kidlington (5.0 miles) and Abingdon.
What it costs in Oxford
For budgeting in Oxford, allow around £27,500–£40,000 for a first-floor extension with 4 m × 3.5 m of new first-floor space (14 m²). That's based on £1,980–£2,860 per m² including VAT for South East England. Keep a contingency of around 10% for things nobody can see until the ground is opened up.
| Spec | Per m² | 4 m × 3.5 m of new first-floor space (14 m²) |
|---|---|---|
| Essential | £1,820–£2,630 per m² | £25,500–£37,000 |
| Standard | £1,980–£2,860 per m² | £27,500–£40,000 |
| Premium | £2,380–£3,430 per m² | £33,500–£48,000 |
Planning and building regulations in Oxford
In England, adding a first floor turns a single-storey extension into one of more than one storey. To be permitted development, the extension as a whole must go no more than 3 m beyond the rear wall of the original house and stay at least 7 m from the rear boundary, with matching materials and roof pitch. Over a side extension it always needs planning permission, costing £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 Oxford homes
Replacing the flat roof
The existing roof usually comes off and is replaced by a new first-floor structure. The room below is exposed for a short time, so we plan temporary weatherproofing and sequence the work to keep the kitchen or living room usable for as long as possible.
Matching the roofline
A first-floor extension often changes how the back or side of the house looks more than the original single storey did. Matching the main roof pitch and materials, and keeping the ridge below the main ridge, usually gives the best result and is expected for permitted development in England.
How we'd run your project
Understand the brief
At your home in Oxford we agree what you need: bedroom count, bathroom, kitchen space, and how much garden you want to keep.
Plans, then approval
Measured survey, design, then the right approval route for your house. We explain each step before we take it.
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.
Questions about first-floor extensions in Oxford
Which postcodes do you cover around Oxford?
We cover Oxford (OX1, OX2 and OX3) and nearby places including Cowley, Kidlington and Abingdon, plus the rest of Oxfordshire. The first site visit is free.
Who handles building regulations for a project in Oxford?
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.
How much does a first-floor extension cost in Oxford?
Our guide for South East England, which covers Oxford, is £1,980–£2,860 per m² including VAT. A typical project with 4 m × 3.5 m of new first-floor space (14 m²) comes to about £27,500–£40,000. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.
What happens to the room below while the first floor is built?
The old roof is removed, so the room below is exposed for a short period. We fit temporary weather protection, plan the work so the roof comes off only when the new structure is ready, and agree with you which rooms will be out of use and for roughly how long.
Will the first-floor extension match my house?
It should, and in England matching materials and roof pitch is a condition of permitted development. We match brick, tile, mortar colour and window style where we can, and tell you at the design stage if an exact brick match is not available, so you can choose between the closest match and render or cladding.
Nearby
Nearby towns we cover for first-floor extensions:
Other extensions in Oxford
- Rear
- Side
- Wraparound
- Part two-storey
- Over a garage
- Semi-detached
- Detached
- Kitchen and bedrooms
- Bedroom and en-suite
All two-storey extension services in Oxford · First-floor extensions across Oxfordshire
The quickest next step is a visit. We'll look at your house in Oxford and give you an honest view of the options.