One of the most common questions clients ask is: "What will actually happen on my project, and when?" This guide walks through a realistic week-by-week programme for a standard single-storey rear extension in London — approximately 20m², masonry construction, with a kitchen relocation and bifold doors.
Pre-Construction Phase (8–16 weeks before site start)
Before a single brick is laid, a well-managed London extension goes through a structured pre-construction phase:
- Planning permission or LDC (if required): 8–16 weeks
- Structural engineer appointment and calculations: 3–5 weeks (can run parallel to planning)
- Building Control full plans application: 4–8 weeks
- Party wall notices served and response received: 2–8 weeks (depending on neighbour response)
- Contractor procurement and programme agreement
- Material long-lead items ordered (bifolds typically have 6–10 week lead times)
The On-Site Programme
Week 1–2: Enabling and Demolition
- Protective boarding through the house (if no side access)
- Internal strip-out at the rear: existing lean-to or conservatory removed, utilities capped or diverted
- Existing rear wall opened up (temporary structural support in place)
- Asbestos survey completed; any ACMs removed before demolition proceeds
- Skip logistics organised; first skip delivered
Week 3–4: Foundations
- Trial pit dug to confirm ground conditions and existing foundation depth (required for Building Control)
- Excavation to specified depth (strip foundations in London clay typically 1.0–1.2m below ground level, deeper near large trees)
- Concrete poured for foundations
- Building Control foundation inspection carried out before backfilling
- Drainage channels laid where new drainage is required
Week 5–7: Superstructure (Walls)
- Damp-proof course installed and inspected
- Brickwork external leaf commenced
- Cavity insulation and inner blockwork proceed in lifts
- Party wall inspection by agreed surveyor (if applicable) at this stage
- Window and bifold door openings formed and lintels installed
- Scaffolding adjusted as walls rise
- Steel beam for rear wall opening installed with temporary support in place
Week 8: Roof Structure
- Flat roof deck or pitched roof structure installed
- Insulation laid
- Flat roof membrane or tiles fixed
- Roof light installation (if included)
- Building Control inspection at insulation stage
Week 9: Making Weathertight
- Bifold doors (ordered in week 1) delivered and fitted
- Rendering or external cladding commenced
- Exterior decorating preparation
Week 10–11: First Fix
- First fix electrics (cables, back boxes, distribution board)
- First fix plumbing (pipe runs, underfloor heating if specified)
- First fix carpentry (stud partitions, structural framing for kitchen layout)
- Building Control first fix inspection
Week 12–13: Plasterboard and Plaster
- Plasterboarding all new walls and ceilings
- Skim plastering
- Drying period begins — plaster in a new extension requires 3–5 weeks to fully dry before decoration and second fix can proceed
- Space heater installed and running to aid drying; dehumidifier if damp weather
Week 14: Floor Preparation and Screed
- Floor insulation installed
- Underfloor heating pipes if specified
- Screed poured (typically 75mm)
- Screed drying period — 4–6 weeks for standard screed, 1–2 weeks for fast-drying compound screed
Weeks 15–17: Second Fix (running in parallel with plaster drying)
Note: Second fix trades begin after plaster is sufficiently dry — approximately 3–4 weeks after skim application for a new extension.
- Second fix electrics (sockets, switches, lighting)
- Second fix plumbing (radiators, heated towel rail, kitchen plumbing connections)
- Kitchen unit installation (if kitchen is being relocated into the extension)
- Internal doors and door furniture
- Skirting boards, architraves, window boards
Weeks 17–18: Tiling and Flooring
- Wall tiling in kitchen and any wet areas (after units are in position)
- Client-supplied flooring installed
Weeks 19–20: Decoration and External Completion
- First and second coat painting throughout
- Kitchen worktops templated and installed (stone worktops are made off-site; allow 2–3 weeks from template to installation)
- External decoration — render painted if applicable
- Landscaping at rear: making good disturbed areas
Week 21: Snagging and Building Control Final Inspection
- Client snagging walk-through
- All snagging items addressed
- Building Control final inspection
- Completion Certificate issued
- Handover
Total Programme: 20–22 weeks on site
This is a realistic programme for a well-managed 20m² single-storey extension in London. Projects that involve:
- More complex structural work or multiple wall removals: add 2–4 weeks
- Larger extensions (30m²+): add 3–6 weeks
- Basement or substructure elements: add 6–12 weeks
- Occupied property constraints: add 10–15% to most stages
What Can Cause Delays
- Adverse weather during external works (particularly in winter)
- Delayed material deliveries — bifolds, bespoke kitchens, stone worktops
- Building Control inspection delays (inspectors are sometimes difficult to book at short notice)
- Structural surprises underground (poor ground conditions, unexpected foundations, services in unexpected positions)
- Client decision delays on finishes, appliances, or layout changes mid-project
rcbGroup
rcbGroup provides a detailed programme before every project starts, updated weekly during construction. We manage the programme actively — chasing material deliveries, coordinating inspections, and adjusting the sequence when unforeseen events require it. Contact us to discuss your extension.