Two-storey extensions for detached houses in Oxford

Before you start in Oxford, here's what applies.

Postcode districts: OX1, OX2 and OX3
County / area: Oxfordshire, England
Price region: South East England
Guide price: £94,500–£127,000 (£2,260–£3,030 per m²)
Approval route: Depends on position: a two-storey rear extension may be permitted development (3 m deep, 7 m from the rear boundary); a two-storey side extension needs planning permission.
Nearest towns: Cowley (2.5 miles), Kidlington (5 miles), Abingdon (5.7 miles)
First visit: Free, no obligation

About a two-storey extension for a detached house

A two-storey extension for a detached house is a two-floor addition to the side, rear or both of a house that stands on its own plot. Detached houses often have room on more than one side, so there is more choice of layout and fewer shared-wall issues. The design still needs to respect boundaries, neighbours' windows and the look of the house.

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

Guide prices for two-storey extensions for detached houses in South East England are around £2,260–£3,030 per m² of new floor space, including VAT. For a typical project with a 3 m × 7 m footprint on two floors (42 m² of new floor space), that's roughly £94,500–£127,000. Design fees, structural calculations and approval fees are separate and listed on our prices page.

Spec	Per m²	A 3 m × 7 m footprint on two floors (42 m² of new floor space)
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

Planning and building regulations in Oxford

In England, a two-storey rear extension on a detached house can be permitted development within 3 m of the original rear wall and at least 7 m from the rear boundary, with matching roof pitch and materials, outside protected areas. Any two-storey side or wraparound extension needs planning permission, costing £548 (or £575 for applications made from 8 December 2026), with a decision due within 8 weeks of validation.

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

Keeping it subordinate

Large detached houses can take a large extension, but councils still expect it to look secondary to the main house. A lower ridge, a modest set-back at the front and matching materials keep the proportions right, even on a wide plot.

Choosing the best side

On a detached house you can often extend on either side or the rear. We look at orientation for daylight, where the stairs and landing are, the distance to each boundary, drains and trees, so the extension goes where it adds the most useful space.

How we'd run your project

Look at the house
We start in Oxford with a free visit: measurements, photos, a look at the loft and drains, and a frank chat about budget.
Drawings and permission
Our designers produce plans and elevations, then we take care of planning or permitted development checks with the council covering Oxford.
Price it properly
Once the engineer's calculations are in, we fix the build price in writing, with a clear list of what's included.
Finish and certify
Second fix, plastering and making good, then building control's final inspection and the completion paperwork.

Questions about two-storey extensions for detached houses in Oxford

Do I need planning permission for a two-storey extension for a detached house in Oxford?

Oxford is in England, so England planning rules apply. Depends on position: a two-storey rear extension may be permitted development (3 m deep, 7 m from the rear boundary); a two-storey side extension needs planning permission. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.

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.

How much does a two-storey extension for a detached house cost in Oxford?

Our guide for South East England, which covers Oxford, is £2,260–£3,030 per m² including VAT. A typical project with a 3 m × 7 m footprint on two floors (42 m² of new floor space) comes to about £94,500–£127,000. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.

Can I extend a detached house on both sides?

Sometimes. With planning permission, a council may accept extensions on both sides if the house stays well proportioned and keeps gaps to the boundaries. It is more common to extend on one side and the rear, or with a wraparound. We look at the plot as a whole before suggesting more than one extension.

Is a detached house extension a better investment than moving?

It often costs less than the gap between your house and a larger one nearby, once property tax, legal fees and removal costs are counted, but that depends on your area. Extending also has limits: every street has a ceiling price. We give you build costs so you can compare them with local asking prices.

Nearby

We also cover places near Oxford, including:

Other extensions in Oxford

All two-storey extension services in Oxford · Two-storey extensions for detached houses across Oxfordshire

Want a figure first? Try our guide price tool, then book a free visit to firm it up.