Electrics and gas
A balanced flue passes through timber cladding and the gap around the flue looks tight. What clearance has not been measured?
The clearance that has not been measured is the gap between the balanced flue and the timber cladding it passes through. The gap looks tight, which is an impression from the visit, not a dimension. The survey has not put a rule on that junction and has not checked it as a gas inspection. A balanced flue through combustible cladding is a place where clearance matters, and this report does not contain the measurement. Looking tight is the observation. The missing figure is the actual clearance, which was never taken.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
Balanced flues draw air and discharge exhaust at the terminal, and the sleeve or the flue body has to pass the wall without the surrounding timber being too close. What too close means is for the appliance instructions and a competent gas engineer, not for a guessed gap in a home survey. The surveyor can photograph the tight-looking joint and say it was not measured. They should not invent a clearance or declare the cladding safe because there was no scorch on the day.
Ask a Gas Safe registered engineer to measure the clearance where the flue passes the timber cladding and to say whether it meets the appliance requirements. Do not pack the gap, open it up, or judge it with a casual glance of your own as if that completed the survey. Tell the solicitor the flue was seen and the clearance was not measured. If there is an installation certificate, ask whether it records this junction. Until a measurement exists, the tight look remains only a look.
What should you ask your surveyor?
- Where does the balanced flue pass the timber cladding, and was the gap measured?
- Did you see scorch or staining, or only a tight-looking clearance?
- Who are you expecting to measure that junction, since the survey did not?
What are the typical next steps?
- Record the flue-to-cladding gap as seen and not measured.
- Do not invent a clearance or a pass from a tight appearance.
- Ask a Gas Safe registered engineer to measure that junction.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
If the cladding is cement board rather than timber, was a clearance still required in the report?
The survey did not measure a clearance either way. If the material is not timber, say what it looked like, but do not invent a measured gap. The tight-looking junction is still unmeasured. No figure was taken at the cladding.
Does a metal plate around the flue prove the gap?
No. A plate is a trim. It can hide the junction rather than show the distance from flue to cladding. The survey has not measured the clearance behind it. Trim is still not a measured gap around this balanced flue.