London House Extension: A Week-by-Week Programme Guide

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

RCB Design & Build

RCB 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.