Understand your extension before you spend on it.
Eight illustrated pages from our London practice covering the decisions that set your cost, programme and risk, from the first brief to the final certificate.
- 8 pages with project photographs
- Updated for 2026
- England rules
Inside the guide
What's inside the guide
- 01
Brief & design
Turn a wish list into a brief an architect can price and draw against.
- 02
Planning vs permitted development
When you need full permission, prior approval or a lawful development certificate.
- 03
Budgets
What the build figure leaves out: fees, VAT, contingency and the finishes gap.
- 04
Programme
Realistic stage-by-stage timings from survey to completion.
- 05
Technical design & building control
Why planning drawings are not construction drawings, and who signs off.
- 06
Party walls
Notices, timings and what the Party Wall etc. Act 1996 asks of you.
- 07
Choosing builders
Like-for-like tenders, contracts, insurance and payment stages.
- 08
Handover checklist & official sources
Certificates to collect before the final payment, plus GOV.UK references.
General guidance only for projects in England, not advice on your specific property. Rules change; check the official sources listed in the guide before you rely on them.
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