What as-built documentation should you keep after an extension?

Beyond the builder's invoice

Extensions interact with planning permission, lawful development certificates, and building regulations. Future buyers need a coherent story.

Keep a structured bundle

Approved drawings: planning permission decision notice and approved drawings; or a lawful development certificate if used.

Building regulations: completion certificate or final notice from building control or a competent person scheme.

Structural package: calculations and specifications for steel, foundations, or openings where applicable.

Party wall: awards or agreed schedules if the Party Wall etc. Act 1996 applied.

Guarantees: roof, glazing, damp proofing, and waterproofing where supplied.

Order these in chronological order inside your Property Passport.

Using Property Passport UK

Start from the address on [Property Search](/search). When you own or manage the home, [claim your Property Passport](/claim/start) and upload Documents with clear dates and sources. Browse more explainers in the [Property Guides library](/guides). This article is general information, not legal, tax, mortgage, or survey advice.