Wall ties and cavity insulation
A cavity brush is visible at the eaves and insulation is piled against it. Has anyone checked the vents below are still open?
No. Nobody has checked that the vents below the cavity brush are still open. A brush is visible at the eaves and insulation is piled against it, which can close the air path the brush and the vents are meant to protect. The survey saw the brush and the piled insulation from the access it had. It did not confirm airflow, did not pull the insulation back, and did not decide that the eaves can still ventilate. A brush is a stop for insulation. It is not proof the vents underneath are clear.
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?
Cavity brushes and eaves vents are there so added insulation does not choke the roof void or the top of the cavity. When insulation is piled hard against the brush, the brush may be doing its job, or it may have been overwhelmed so material sits across the vent. The survey cannot tell those apart without looking under the pile and seeing daylight or a clear slot. That look did not happen. Blocked eaves ventilation is a moisture risk for timbers. It has not been confirmed or dismissed.
If the loft is to be used as evidence for a lender or for works, ask a contractor to lift the insulation at the eaves and show whether the vents are open, and keep that note separate from this survey. Do not tell anyone the roof is ventilated because a brush was visible. The visible brush is the finding. The open or shut state of the vents below it is the check that is still missing.
What should you ask your surveyor?
- Were the vents below the brush seen clear, or only the pile above them?
- Did anyone pull the insulation back at the eaves?
- Is a visible brush being reported as proof of airflow?
What are the typical next steps?
- Treat the vents below the brush as unchecked.
- Ask a contractor to lift the eaves insulation if you need the vents seen.
- Do not report a visible brush as open ventilation.
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
Does piled insulation mean the brush has failed?
Not necessarily. The pile shows insulation against the brush. It does not show that material has passed the brush or that the vents below are blocked. It also does not show they are clear. That is why the check matters and why it has not been done. Leave both the failure and the all-clear unstated.
Was the cavity insulation itself tested for damp or settlement?
No. The survey saw insulation piled at the eaves against a cavity brush. It did not test the insulation for moisture, did not measure how far it has slumped, and did not decide the cavity fill is performing. Those would be further checks. The unanswered point in this report is whether the vents below the brush are still open.