House extensions in Oxford and Oxfordshire

An extension is the biggest building job most people will ever have done at home, and it happens while you are living there. We plan the work so you keep a working kitchen and bathroom for as long as possible, we keep the site clean at the end of every day, and you have Harry’s number throughout. We build energy-efficient extensions, with insulation, glazing and heating specified to keep running costs down.

The photos on this page follow a recent single-storey rear extension from the dug-out foundations to the rendered finish.

Types of house extension

• Single-storey rear extension. The most common kind, usually for a bigger kitchen, dining or family room opening onto the garden.
• Side-return extension. On many terraced and semi-detached houses, the narrow strip beside the back of the house can be built over to widen the kitchen.
• Wraparound extension. A rear and a side extension built together, wrapping around the corner of the house.
• Two-storey extension. A bedroom or bathroom upstairs as well as a room below.
• Garage conversion. Turning an attached garage into a room, covered further down this page.

Do you need planning permission for a house extension?

Many single-storey rear extensions are permitted development, which means they can be built without a planning application. When we checked the rules in September 2026, the main limits for a house were:

• A single-storey rear extension can come out up to 3 metres from the original back wall of an attached house, or 4 metres for a detached house, and be up to 4 metres high.
• With prior approval from the council, those depths go up to 6 and 8 metres, except in a conservation area.
• Within 2 metres of a boundary, the eaves can be no higher than 3 metres.
• A side extension has to be single storey, no more than 4 metres high and no wider than half the original house.
• All the extensions together can cover no more than half the land around the original house.

In a conservation area, side extensions and extensions of more than one storey always need planning permission. Flats and maisonettes have no permitted development rights, listed buildings need listed building consent, and some newer houses had these rights removed when they were built. Oxford has 18 conservation areas; our Oxford planning guide lists them and links to the official rules.

We will tell you at the site visit whether you are likely to need an application. Your architect or the council’s planning team confirms it.

Planning and drawings

Where drawings and structural calculations are needed we work with your architect or engineer, or can introduce one. If you want proof that an extension is permitted development before you start, the council can issue a lawful development certificate.

Do extensions need Building Regulations approval?

Planning permission and Building Regulations are separate. Every extension needs Building Regulations approval, even when it needs no planning permission. The foundations, structure, drainage, insulation, ventilation and fire safety are all checked, and a building control inspector visits at set stages of the work. When the extension passes the final inspection you get a completion certificate. Keep it with the deeds: a buyer’s solicitor will ask for it when you sell.

Do you need a party wall agreement?

If the extension is built on or close to the boundary, or the foundations are dug near a neighbour’s, the Party Wall etc. Act 1996 applies. Notice goes to the neighbours before the work starts: one month ahead for building on the boundary line or digging close to their foundations, and two months ahead for work to a shared party wall. If they agree in writing, work can go ahead. If they do not, surveyors settle it with a party wall award.

How an extension job runs

1. A site visit, then a written quote that lists what is and is not included.
2. Drawings, structural calculations and approvals, with your architect and engineer.
3. Groundworks: digging out, foundations and drainage.
4. Walls, floor and roof, until the extension is weathertight.
5. Knocking through into the house, with steels where a wall comes out, then windows and doors.
6. First fix plumbing, heating and electrics, then plastering.
7. Second fix, flooring, kitchen or bathroom fitting and decoration.
8. The final Building Control inspection, and we walk through the finished extension with you.

Garage conversions

We also convert attached garages into habitable rooms, such as a playroom, home office or extra bedroom. This follows the same route as other extension work, with insulation, damp-proofing, flooring, plastering and decoration to match the rest of the house.

What customers say

“You can trust all the other reviews - Harry and his team do high quality work, have great communication, and work hard over long days to get the job done. Would definitely recommend! For us they installed load bearing wall supports from a structural engineers plan, and plastered it after sign off from building controls. All went smoothly with no issues and we’ll definitely use Oxford Direct Builders again.”

Dave, August 2025, load-bearing wall supports and plastering

“Looking for the removal of two internal walls and a window contacted Hajri of Oxford Direct Builders - I was very impressed that he ensured that he fully understood what I required and by his attention to detail in obtaining bricks to match the existing - I extended the work to include the replacement of a wall and garden gate - I am delighted with the finished work completed to a high standard and that Hajri always left everything clean and tidy”

Mike, September 2024, wall removal, garden wall and gate

Planning a loft conversion or a renovation as well? We can price them together.