Can I live in my house during an extension?

Yes — most clients stay in residence. We set up a temporary kitchen in another room (hire kitchen £400/month) and keep at least one toilet and bathroom functional throughout. The disruptive phase is the first 3–4 weeks (groundworks, demolition, scaffold). After the extension is weather-tight (typically week 5–6), the project becomes much more liveable.

What causes delays to house extensions?

The main causes: party wall disputes (adds 4–8 weeks), planning delays (adds 2–6 weeks), structural surprises in groundworks (London clay and made ground can delay foundation works by 1–3 weeks), specification changes mid-build, and delivery lead times on bespoke glazing (bifolds and sliders can take 6–10 weeks — we order at contract signature to avoid delays).

Does weather affect extension timelines?

Groundworks and brickwork are weather-sensitive — concrete shouldn't be poured in frost, and brickwork needs mortar to cure properly. We account for weather in our programme. Once the extension is weather-tight (typically week 4–6), interior works are unaffected by rain. Summer builds are faster; winter builds can add 2–3 weeks in extreme cold spells.

How Long Does a House Extension Take? London 2025

How Long Does a House Extension Take?

A single-storey rear extension takes 10–16 weeks on site; a side return 10–14 weeks; a wraparound 16–20 weeks; a double-storey 16–22 weeks. Add 4–6 weeks for design and building regulations submission. If planning permission is required, add 8–12 weeks. Total project timeline from first consultation to handover: 18–40 weeks.

Extension timeline by type

Timeline varies by extension type and complexity. A side return extension (3–4m wide, single-storey) typically takes 10–14 weeks on site — it's the quickest type because it infills an existing narrow alley, with less new structure than a full rear projection. A single-storey rear extension (4m deep) takes 12–16 weeks. A 6m rear: 14–18 weeks. A wraparound (combining side and rear) adds complexity at the corner junction and typically runs 16–20 weeks. A double-storey rear or side extension is the most complex: foundations must carry two floors, first-floor structure needs careful co-ordination with existing floors, and the roof junction requires skilled detailing — 16–22 weeks on site.

Pre-construction phase breakdown

Before ground breaks, the pre-construction phase takes 6–20 weeks depending on the planning route. Measured survey and design: 2–4 weeks. Structural calculations: 1–2 weeks (usually concurrent with design). Building regulations submission: 2–3 weeks to process. Party wall notice: served at design confirmation, 2-month minimum before structural work, agreement 2–6 weeks for neighbours in agreement or up to 8 weeks for disputed. Permitted development route (LDC): 6–8 weeks application time. Full planning: 8–12 weeks statutory, add 2–4 weeks for preparation. In practice, a PD extension with clear neighbour co-operation: total pre-construction 8–12 weeks. Full planning extension: 14–20 weeks pre-construction.

Month-by-month breakdown for a 4m rear extension

Month 1 (Weeks 1–4): Groundworks — demolition of existing rear wall, foundation excavation, concrete pour, drainage diversion. This is the disruptive month: noise, dust, ground disturbance. Scaffold up around week 3. Month 2 (Weeks 5–8): Superstructure — blockwork walls, structural steel installation over the opening in the existing rear wall, new flat roof deck laid. Extension is weather-tight by end of week 8. This is when the client experience improves significantly. Month 3 (Weeks 9–12): First fix MEP — new wiring, plumbing, UFH if specified, drainage. Insulation, plasterboard. Month 4 (Weeks 13–16): Second fix — final electrics, plumbing connections, tiling, flooring, bifold installation, decoration, kitchen fit-out. Week 16: pre-handover snagging and client walk. Handover.