Extension Project Checklist: Step-by-Step Guide
Your complete checklist for planning and building an extension in London. Every step from initial ideas through to moving into your new space.
Project Overview
- Phase 1: Initial Planning (Weeks 1-4)
- Phase 2: Design (Weeks 5-12)
- Phase 3-6: Approvals to Completion (Weeks 13-44+)
- Get instant cost estimate for your extension (Free)
Phase 1: Initial Planning (Weeks 1-4)
What do you need? Extra bedroom, larger kitchen, home office?
Include 15-20% contingency. Consider professional fees, not just build costs.
Use our PD checker to see what you can build without planning.
Conservation area? Listed building? Tree preservation orders?
Early communication prevents problems later. Good neighbours make projects easier.
Phase 2: Design (Weeks 5-12)
Get recommendations, review portfolios, compare quotes (3 minimum).
Measured survey of existing building. May need topographical survey too.
Sketch options showing different approaches. Agree on direction before detail.
Floor plans, elevations, sections. Enough detail for planning application.
Written justification for your design. Required for conservation areas.
Phase 3: Planning & Approvals (Weeks 13-24)
£258 fee for householder applications. 8 week determination period.
£129 fee. Confirms your development is permitted. Good for resale.
If building on or near boundary. 2 months notice before work starts.
For beam calculations, foundation design, structural drawings.
Full plans or building notice. Full plans recommended for extensions.
Phase 4: Procurement (Weeks 20-28)
Detailed construction drawings for builders to quote from.
Written specification of materials, finishes, workmanship standards.
Send identical information. Allow 3-4 weeks for quotes.
Visit completed projects. Verify public liability and employer's liability.
JCT Minor Works or similar. Include scope, price, timeline, payment terms.
Phase 5: Construction (Weeks 28-44+)
Agree programme, access, working hours, site setup, communication.
Building control inspection at foundation stage before concrete pour.
Walls, steel, roof construction. Multiple building control inspections.
Pipes and cables before plastering. Last chance to change positions.
Walls finished, sockets and switches installed, kitchen fitted.
Final finishes. Walk through with builder, create snagging list.
Phase 6: Completion
Inspector signs off work. Completion certificate issued.
Electrical Part P certificate, gas certificate, FENSA for windows.
Hold 2.5-5% retention for defects liability period (typically 6-12 months).
Operation manuals for appliances, warranties for materials, guarantee certificates.
Notify insurer of increased floor area and rebuild value.
Keep planning approvals, building control certificate, warranties for resale.
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