When to test
The home should be practically complete, with the outside envelope in its final state, so that the result represents the finished building. Decorating can usually wait, but anything that forms part of the airtight layer can't.
A readiness checklist
Your tester's own checklist and the test method have the final say. As a starting point:
- Windows and external doors fitted and able to close properly, including thresholds and seals.
- Service penetrations sealed permanently: pipes, cables and ducts through the walls, floors and ceilings.
- Water traps filled in sinks, baths, showers and appliances, so drains don't act as leaks.
- Airtightness details finished: the membranes, tapes and seals shown in the design.
- Nothing missing or broken: if a window or door is broken or missing, tell the tester before the visit. A temporary seal may be possible, but it has to be robust and recorded in the report.
- Internal doors open, so the whole home is tested as one space.
- Power on for the test fan, safe access to an external door for the fan, and the plot clearly numbered.
- No trades working in the plot during the test, opening doors and windows.
What the tester closes and seals
The test method sets out which openings are closed and which are temporarily sealed during the test. Under CIBSE TM23 (2022), the approved methodology, trickle vents are closed but not sealed. Mechanical ventilation and other intentional openings are dealt with as the method sets out, and the tester records what was done, often with photos. Don't seal anything yourself unless the tester asks; sealing things that should be left as built can make the result meaningless.
Weather and timing
Testers record the wind conditions during the test, because wind can affect the result. If the forecast is poor, talk to the tester; it may be better to move the visit than to waste it.
Answer the readiness check honestly
If you use TestConnect, the site contact is asked the day before whether the plot is ready: yes, no or not sure. "No" stops the trip and tells everyone. "Not sure" asks the tester and job owner to get in touch. Saying "yes" when it isn't costs a visit, a fee and a slot in your programme. See what site managers see.
This guide is general guidance, not a test method. Follow your tester's instructions and check anything you're unsure about with them, their scheme, or your building control body.
Sources
- CIBSE TM23: Testing Buildings for Air Leakage (2022)
- CIBSE Journal: trickle vents closed but not sealed; recording wind and preparation
- ATTMA Technical Standard L1, Issue 1 (2010, since replaced): water traps, service penetrations, internal doors, completed envelope
- Doncaster Council building control: air testing FAQs ("practically complete")
- Approved Document L, Volume 1: Dwellings (GOV.UK)
Last checked: October 2026.