How long does a house extension take?
Most single-storey extensions take 10 to 16 weeks on site, and two-storey extensions 16 to 24 weeks. Before that, design and approvals usually take 2 to 4 months: a householder planning decision is targeted at 8 weeks, prior approval at 42 days, and building regulations drawings take a few weeks.
Before work starts
- Survey and design: 2–6 weeks, depending on how many options you explore.
- Planning: about 8 weeks for a householder application, 42 days for prior approval, around 8 weeks for a lawful development certificate.
- Building regulations and structural design: 2–5 weeks, often alongside planning.
- Party wall notices: one or two months' notice, which can run in parallel.
On site: a typical single-storey timeline
- Weeks 1–2: set-up, excavation and foundations.
- Weeks 2–4: drainage, ground floor slab and walls up to roof level.
- Weeks 4–6: roof structure, roof covering, lanterns and rooflights.
- Weeks 6–8: windows, doors, and opening up into the house.
- Weeks 8–12: first fix electrics and plumbing, insulation, plastering.
- Weeks 12–16: floors, second fix, kitchen and decoration.
What causes delays?
- Long lead times on bespoke glazing, steel and kitchens.
- Unexpected ground conditions or drains.
- Changes to the design after work has started.
- Very wet or frozen weather during groundworks.
Can I live at home during the work?
Usually yes. Most of the work happens outside the existing house until the rear wall is opened. We plan that stage carefully and keep the house weather-tight and secure throughout.
This guide is general information, not legal or professional advice for your property. Rules can change; we check the current position for your address at the survey.