How do I know if woodworm is still active?

Look for fresh bore dust around the holes — pale, gritty and often in trails down vertical timber — and for dead adult beetles nearby. Clean-edged holes with fresh frass suggest activity. Grey, dusty old holes with nothing beneath them usually mean it finished years ago.

Does woodworm mean my floor is unsafe?

Usually not. A scatter of flight holes in board faces is cosmetic. What matters is whether the section of a load-bearing timber has been lost, particularly at joist ends and in stair strings, and whether the damp that fed the infestation has also caused rot.

Do I need chemical treatment?

Only if the infestation is genuinely active, and only alongside fixing the damp. The Property Care Association's position is that it is essential to establish activity before treating, and that treatment is not justified where the infestation has died out. Drying the timber is what stops it coming back.

Why is it usually near the ground floor or the loft?

Because those are the damp, poorly ventilated places. Sub-floor voids with blocked air bricks and cold roof spaces with condensation hold enough moisture in the timber for beetles to breed. Heated, ventilated rooms rarely do.

Caution

Updated 30 August 2026

Woodworm Holes In Timber

Small round holes in floorboards, joists or roof timbers, sometimes with fine dust beneath them.

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What's happening?

Woodworm is the larval stage of wood-boring beetles, and the holes you see are exit holes made by adults leaving the timber. The Property Care Association gives the common furniture beetle's exit holes as roughly 1–2mm across, which is what most homeowners find. The hard part is not spotting the holes — it is deciding whether anything is still living in there. Small piles of bore dust, called frass, around the holes indicate activity, and they show up most clearly as trails on vertical surfaces. Adult beetle carcasses are one of the best indicators. Old holes with no dust and grey, dirty edges are usually a historic infestation that died out long ago.

What usually causes it?

Sustained damp in the timber — the PCA is clear that timber kept dry is highly unlikely to sustain an infestation
Unheated, unventilated voids such as lofts and sub-floor spaces where humidity stays high
Blocked or missing air bricks starving a suspended timber floor of ventilation
A leak, failed damp proofing or penetrating damp raising the moisture in nearby joists and boards
Untreated second-hand or reclaimed timber bringing an existing infestation into the house
Sapwood in older softwood boards and joists, which the common furniture beetle prefers to heartwood
Condensation in a cold roof space wetting rafters and ceiling joists over successive winters

Is it dangerous?

It depends entirely on extent and location. Cosmetic flight holes in a handful of floorboards are not a structural matter. Heavy, long-running infestation can weaken timber significantly, and in a joist end, a rafter or a stair string that is a genuine safety issue. Because active woodworm is a damp symptom, the moisture behind it usually matters more than the beetle: the same conditions bring wet rot, and rot does far more structural damage. Never accept a diagnosis of active woodworm without someone identifying where the water is coming from.

Can I fix it myself?

You can gather the evidence. Lay a sheet of dark paper or tape below the holes, leave it a week or two and look for fresh, pale bore dust — fresh frass is bright, old dust is grey. Note whether the holes have sharp, clean edges. Improve the ventilation you can reach: clear blocked air bricks, deal with the leak, ventilate the loft. What you should not do is spray a fluid on a floor and consider it dealt with, because surface treatments do not reach larvae deep in a joist and they do nothing about the damp that let the infestation establish.

When should you call a carpenter?

Call a carpenter where timber has been weakened and needs cutting out and replacing — soft joist ends, a chewed stair string, boards that flex over an infested area. Have a timber or damp specialist establish whether the infestation is active and what is wetting the wood; the PCA is explicit that treatment is not justified where an infestation has already died out. If holes are in roof timbers or joist ends, get it looked at rather than left.

What will the carpenter actually do?

Lift boards and open up access so the joists, plates and bearings can actually be inspected, not just the visible surface
Sound and probe affected timber to judge how much section has been lost
Cut out and replace structurally weakened joists, joist ends, boards and stair components in pretreated timber
Reinstate sub-floor ventilation — clear or add air bricks and remove debris bridging the void
Work alongside a timber or damp specialist so the moisture source is fixed before new timber goes in
Refix the floor or the affected structure so the repair carries load properly

Frequently asked questions

We’re happy to answer all your questions.

Sources & References

Rotten Door Frame At The BottomCaution Rotten Window SillCaution Blocked Or Painted-Over Air BricksCaution

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