In short: the usual order is drawings → check planning → structural engineer → building regulations → party wall (if needed) → get quotes and book your builder → order long-lead materials → build. Your first call is normally an architect or architectural designer. From first idea to finished room, a single-storey extension typically takes 6–9 months.
An extension is as much about organising the right people in the right order as it is about the building work. Do it in the wrong order and you get delays, abortive fees and a builder standing idle. Here is the sequence, who to contact, and how long each stage really takes in 2026.
Who to contact first
- Architect or architectural designer — usually your first call. They turn your ideas into drawings for planning and building regs, and help you get the most from the space.
- Your local planning authority — to confirm whether you need planning permission or can use permitted development. Many councils offer paid pre-application advice, which is cheaper than a refused application.
- Structural engineer — calculates beams, lintels and foundations once the design is settled.
- Building control — your council or an approved inspector, who checks the work meets regulations.
- Party wall surveyor — only if a shared wall or boundary is affected.
- Builder and bricklayer — get these booked early. Good trades are booked weeks or months ahead, so line them up well before you want to start.
Do you even need planning permission?
Many single-storey rear extensions are permitted development and need no planning application at all — broadly, up to 3 metres from the original rear wall on a semi-detached or terraced house, or 4 metres on a detached house, within height limits and provided you are not in a conservation area, Article 4 area or listed building. Larger extensions (up to 6 or 8 metres) can be possible under a prior-approval process. Check your position on the Planning Portal and confirm with your council before you commit.
Planning and building regs are two different things
Planning permission is about whether you can build it; building regulations are about how it is built — structure, insulation, damp-proofing, fire safety. Even if you do not need planning permission, you still need building regulations approval, and the work is inspected as it goes up. See the gov.uk building regulations guidance.
The Party Wall Act
If your extension affects a shared (party) wall or is built up to the boundary, you must serve notice on the neighbour before work starts under the Party Wall etc. Act 1996. They have 14 days to respond, and if they dissent the process can take anywhere from a couple of weeks to several months — so start it early. The gov.uk party wall guidance explains it.
How long each stage takes (2026)
| Stage | Typical time |
|---|---|
| Design and drawings | 4–8 weeks |
| Planning decision | ~8 weeks from validation (16–20+ if listed/conservation) |
| Building regulations approval | 3–6 weeks |
| Booking builder & ordering materials | 4–8 weeks (bifolds 8–12 weeks) |
| Construction on site | 8–16 weeks (single-storey) |
The order of work on site
Once you start building, the sequence is broadly: foundations → below-ground brick and blockwork up to damp-proof course → floor → walls and brickwork → roof → windows and doors → first fix → plastering → second fix → decorating. The brickwork sits early in that run, which is why it pays to have your bricklayer booked before the foundations are even poured.
A tip on lead times
The two things people leave too late are booking a good builder and ordering long-lead materials like bifold doors and roof lanterns. Sort both as soon as your drawings are settled, not once building starts.
For budgets, see single-storey extension cost; for how the brickwork ties into your existing house, see joining an extension to an existing wall.
Frequently asked questions
Who do I contact first for a house extension?
Usually an architect or architectural designer, to turn your ideas into drawings. From there you check planning with your local authority, bring in a structural engineer, arrange building control, and book a builder and bricklayer — the good ones get booked months ahead, so contact them early.
Do I need planning permission for a single-storey extension?
Often not. Many single-storey rear extensions fall under permitted development — up to 3 metres from the original rear wall on a semi or terrace, or 4 metres on a detached house, within height limits. Conservation areas, listed buildings and Article 4 areas are exceptions. Always confirm with your local planning authority first.
How long does a house extension take from start to finish?
A single-storey extension typically takes 6 to 9 months from first drawings to finished room: roughly 4 to 8 weeks design, about 8 weeks for a planning decision, 3 to 6 weeks building regs, 4 to 8 weeks to book a builder and order materials, and 8 to 16 weeks on site.
What is the right order to organise an extension?
Design and drawings first, then confirm planning, then structural engineer and building control, then serve any party wall notices, then get quotes and book your builder, and order long-lead items like bifold doors early. Building on site then runs foundations first and finishes with decorating.
Getting a price for your extension
Every extension is different, so the brickwork is priced after we have seen the job. If you are planning an extension in Hampshire, Berkshire or Surrey, see our extension work or send us the details and we will come and look.