Which documents should you keep after a house extension?

An extension generates more paperwork than most people expect, and almost all of it arrives by email, in a WhatsApp thread, or as a printed sheet handed over on site. Five years later, when a buyer's solicitor asks a simple question, that paperwork is usually the hard part.

The core set

• Planning permission decision notice, or written confirmation that the work was permitted development
• Approved drawings, including any revisions issued during construction
• Building Regulations application and the final completion certificate
• Structural calculations and any structural engineer's sign-off
• Party wall award, where one was required

Certificates issued by trades

• Electrical installation certificate and any minor works certificates
• Gas Safe or OFTEC commissioning paperwork for heating work
• FENSA or CERTASS certificates for windows and external doors
• Insulation, air-tightness or SAP documentation where applicable

Warranties and guarantees

Roofing, damp proofing, structural waterproofing, underfloor heating, boilers and windows commonly carry separate guarantees with different lengths and different registration requirements. Record who issued each one, its start date and its expiry date, because a guarantee you cannot evidence is difficult to rely on.

Photographs before things are covered

Foundations, damp proof courses, structural steels, insulation, first fix plumbing and electrics, and drainage runs are all invisible once finished. Dated photographs of each are the cheapest record you will ever create and the most useful one when questions arise later.

Project Passport keeps these records together in one permanent digital record of your property, so the drawings, approvals, certificates, warranties and photographs of every project stay findable years after the work finishes. It is an independent record-keeping platform: it complements, and does not replace, Building Control, HM Land Registry, conveyancers or professional advice.