Why do some quotes show shorter programmes?

Tight programmes pressure subcontractors and quality. Realistic London 2026 programmes for typical scopes are 12–18 weeks for single-storey, 14–20 weeks for side return.

What causes programme slip?

Top three: weather (winter ground-work delays), client variations (extra scope, undecided material specs), discovery (rotten joists, unexpected foundations).

Can I live in during the build?

Yes for extensions (kitchen disrupted but liveable) and loft (top floor only). Whole-house renovation — recommend renting out for 8–16 weeks during heaviest disruption.

What is Builderr's typical programme?

Single-storey 12–16 weeks, side return 14–18 weeks, loft 10–13 weeks, whole-house 22–32 weeks. We commit to programme dates with weekly progress reports against milestone schedule.

Quick Answer

How Long Does a London Extension Take to Build?

Typical London extension construction programmes: single-storey rear 12–18 weeks, side return 14–20 weeks, double-storey side extension 18–26 weeks, loft conversion 10–15 weeks and whole-house renovation 22–36 weeks. Programme runs: weeks 1–2 strip-out + foundations; weeks 3–6 superstructure; weeks 7–10 roof + first fix; weeks 11–14 plaster + second fix; weeks 15+ kitchen, finishes, snagging. Heritage and listed work adds 25–50%.

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Single-storey rear (PD): 12–18 weeks

Weeks 1–2: strip out, set-up, foundations excavated, drainage diversions. Weeks 3–4: foundations poured, oversite, brick to DPC, structural steel set. Weeks 5–7: brick + block superstructure, roof timbers, flat roof or pitched. Weeks 8–10: roof finish (warm flat roof + lantern or pitched + tile), windows and bifolds installed, first-fix M&E, screed. Weeks 11–13: plaster, second-fix M&E, kitchen install. Weeks 14–17: finishes, decoration, flooring, snagging.

Loft conversion: 10–15 weeks

Weeks 1–2: scaffolding up, roof opened, structural steel installed (3–5 steels typical). Weeks 3–5: dormer or hip-to-gable built, roof closed and watertight, windows in. Weeks 6–8: floor structure, first-fix M&E, stair installed, insulation. Weeks 9–11: plaster, second-fix, bathroom installed. Weeks 12–14: finishes, decoration, building control completion.

Whole-house renovation: 22–36 weeks

Strip-out 2–3 weeks. Structural alterations + extension (if included) 8–12 weeks (parallel programme). Rewire + replumb 3–4 weeks. Plaster 2–3 weeks (dry 2 weeks before paint). Kitchen + bathrooms 3–4 weeks. Finishes + decoration 4–6 weeks. Snagging 1–2 weeks. Parallel workstreams matter — good main contractor sequences trades so plumber finishes pipework just before plaster, electrician returns for second fix just after plaster.

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