Timber decay and woodworm
Fine dust sits on the plywood fixed under the ceiling, near old flight holes. Has the survey declared an active attack, or dust that still needs telling apart from fallen debris?
No fine dust on the plywood fixed under the ceiling, near old flight holes, is a declared active attack. The survey has not separated that dust from fallen debris, so it has not called the attack live. Pale grit can be old torching, which is mortar bedding once used under slates. That debris is not automatically woodworm frass, and it is not automatically a slate failure. Dust that still needs telling apart should stay undecided. The visit has not sent the house to be sprayed.
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?
Bore dust from insects has a grain and usually sits tight under the holes that made it. It differs from mortar crumbs, plaster and soot that fall through gaps onto a board fixed below. Torching, where it was used, is that old mortar, and pieces of it on later plywood are a debris note. They do not, by themselves, mean the slates have failed or that an insect is at work. Nearby holes make the mix easy to misread.
If the dust must be identified, ask a timber specialist to see it in place, not to treat on the way through the hatch. Cleaning it up first destroys the evidence. Keep the plywood, the old holes and the dust as separate lines in any later note. An active attack is a conclusion this visual survey has withheld. Fallen torching, if that is what the grit proves to be, is debris from the roof bedding, not a spray instruction.
What should you ask your surveyor?
- Where is the dust sitting, and did you call it frass or leave it undecided?
- Are the flight holes old, and was any fresh dust coming out of them?
- Could the material on the plywood be torching or other debris from above?
What are the typical next steps?
- Leave the dust where it lies until someone competent has identified it.
- Do not commission a spray because dust sits near old flight holes.
- If the grit is torching, keep that mortar debris apart from any insect note.
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
Is torching debris the same thing as woodworm frass?
No. Torching is old mortar bedding from under the slates. It is not automatically insect dust, and it is not, by itself, a failed slate.
Does dust on the plywood prove the attack is active?
No. Dust near old holes still has to be told apart from fallen debris. The survey has not declared an active attack from what is lying there.