An extension is one of the biggest projects most people take on at home. A few decisions early on make every later stage smoother – here’s where to start.
1. Be clear what the space is for
“More room” isn’t a brief. A kitchen you can eat in, a downstairs room for an older relative, a quiet office – each one suggests a different size, shape and position. Write down how you’ll use the space day to day, and what bothers you about the house now. That list will steer the design more than anything else.
2. Set a budget, with room to spare
Decide what you’re comfortable spending before anything is drawn, and keep a contingency on top – something in the region of 10 to 15 per cent is a sensible starting point. Remember the costs beyond the build itself: drawings, structural calculations, planning and Building Control fees, and the kitchen, flooring and furniture that go into the new space.
3. Check what permission you need
Many single-storey extensions come under permitted development and need no planning application. In outline, for a house in England:
- a single-storey rear extension can usually go out 3 metres from the original back wall of a semi-detached or terraced house, or 4 metres for a detached house;
- it can be up to 4 metres high, but the eaves can be no higher than 3 metres if it’s within 2 metres of a boundary;
- a single-storey side extension can be no more than half the width of the original house;
- materials should be similar in appearance to the existing house.
Deeper single-storey rear extensions – up to 6 metres, or 8 for a detached house – are possible through a quicker “prior approval” process, where the council consults your neighbours. Two-storey extensions have much tighter limits, and homes in conservation areas or National Landscapes, listed buildings and flats generally need a full application.
4. Drawings, Building Regulations and the neighbours
Almost every extension needs Building Regulations approval, whatever the planning position – it covers structure, insulation, fire safety and drainage. You’ll normally need drawings and, for anything structural such as steel beams, calculations from a structural engineer.
If the work involves a shared wall, building on the boundary, or digging foundations close to a neighbour’s, the Party Wall Act applies and you must give your neighbours written notice before work starts. Talking to them early, before any notice arrives, makes the whole thing easier.
5. Choose your builder
Ask to see work they’ve finished, and to speak to people they’ve built for. Get prices in writing that set out what’s included, so you can compare like with like. Check how they’ll handle the stages you care about most – access, mess, the weeks when the back of the house is open – and who you’ll speak to when you have a question.
6. Plan for living through it
Most families stay at home during an extension. The bulk of the build goes up outside the existing walls; the disruptive part is when the two are joined. Plan a temporary kitchen if yours is affected, and keep a clear route for deliveries.
We build extensions and conversions in and around Wantage and Grove, with the carpentry, finishing and landscaping done by the same firm. See extensions and conversions, or tell us about your plans.
This is general guidance for England, not legal or planning advice. Check the current rules with your local planning authority or the Planning Portal before you start.
