How long does an extension actually take, start to finish?
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Short answer: from first design conversation to a finished, decorated room, a typical extension project spans several months, and the build itself is usually the shorter half. Design and approvals commonly take longer than people expect: the statutory target alone for deciding a householder planning application is 8 weeks. On site, a straightforward single-storey extension is measured in weeks, not days, and weather, structural surprises and made-to-order items are the honest reasons programmes move.
The stages, in order
- Design and survey. Measured survey, design development, your decisions on layout and finish. Weeks, driven mostly by how quickly decisions land.
- Approvals. Planning where needed (8-week statutory determination target for most householder applications, per gov.uk), building regulations submission, and party wall notices where they apply, which require between 2 months and a year of notice (gov.uk).
- Procurement. Structural steel, windows and glazing are made to order and lead the programme. Ordering them the day the design is fixed is how weeks are saved.
- The build. Groundworks, structure, weathertight, first fix, plaster, second fix, decoration. Plaster drying and screed curing are physics and will not be rushed.
- Sign-off. Building control completion, electrical certification, snagging and handover.
The dates that matter are written ones. Your quote comes with a written programme, updated through the build. A builder quoting from memory is guessing with your kitchen.
Working towards a date? A free consultation will tell you plainly whether it is achievable, with no obligation.
Book a Free ConsultationWhat genuinely moves a programme
- Decision speed on kitchens, glazing and finishes, which gate the orders
- Ground conditions discovered at excavation
- Weather during groundworks and structure
- Party wall dissent starting the surveyor process
- Changes mid-build, which we price and programme in writing before proceeding
When this is not what you want to hear
If you need the extension finished for a fixed date a few weeks away, the honest answer is that no responsible builder can promise it from a standing start. Approvals and lead times alone can consume that window. Come to us with the date and we will tell you plainly whether it is achievable before you commit to anything.
Quick answers
How long does the planning stage take?
The statutory target for deciding most householder planning applications is 8 weeks from validation, per government guidance. Design time before submission, and any party wall notice periods, sit on top of that.
How long is the actual build?
It depends on size, structure and finish level. Your written programme arrives with your quote.
Can I live in the house during the work?
Usually yes for rear extensions, with dust and disruption managed and services kept running as long as possible. Kitchen replacements are the hard part; we plan temporary arrangements with you before the build starts.
Next step: a free consultation on your actual project, or browse the rest of the advice hub.