Woodworm in roof timbers and beams: what should you do?

Holes in a beam don't always mean trouble. Plenty of woodworm died out decades ago.

The answer in 2 lines. Small holes in timber and dust underneath are the signs of 'woodworm', the larvae of wood-boring beetles. In England, the most common is the common furniture beetle (small round holes, in furniture, floorboards and roof timbers). Death watch beetle attacks old, damp hardwood such as oak. The house longhorn beetle (larger oval holes in softwood) is rarer and mostly found in parts of Surrey, but it can weaken a roof. First, find out whether the attack is still active. Then look for damp, which is usually the real cause. Damage to roof timbers or beams is a job for an independent surveyor.

The 4 steps

Look at the holes: sharp edges with pale, fresh wood inside, and fine dust (frass) below, point to recent activity. Rounded, dark holes usually mean an old attack.
Test it: clean up the dust, or tape acid-free tissue over the holes, and check for new holes or fresh dust. Beetles mostly come out in spring.
Look for damp: roof leaks, condensation, wet patches, old roofing felt. Without damp, attacks tend to die out.
Get an independent opinion on roof timbers or beams from a surveyor, not just a report from a firm that sells the treatment.

Stop: danger

A beam sagging, creaking, or new cracks in the ceiling below: take everything stored off that area, don't walk on it, and get a structural engineer or qualified surveyor in quickly.
In a loft, walk only on boards or the joists: the ceiling between the joists won't take your weight.

Which beetle is it?

	Common furniture beetle	Death watch beetle	House longhorn beetle
Timber attacked	Softwood and hardwood: furniture, floorboards, joists, roof timbers	Old hardwood, especially damp oak, in older buildings	Softwood roof timbers
Holes	Small, round, often lots of them	Few obvious holes; adults can come out through cracks	Larger and oval
Other signs	Fine dust in small piles	Tapping sound in spring	Bore dust; sometimes chewing noises
How serious	Usually surface damage to the sapwood	Can be serious in old structural oak	Can weaken roof timbers; mainly found in parts of Surrey

Because of the house longhorn beetle, building regulations require softwood roof timbers to be treated in certain areas. The list is in table 1 of Approved Document A (PDF, GOV.UK), in the section on areas at risk from house longhorn beetle. Your council's building control team can confirm whether your area is on it.

Treatment: what you can do yourself, and where to stop

A piece of furniture or a small object: an insecticide sold to the public for woodworm can be enough. Follow the label exactly, work outside or in a well-ventilated room, wear gloves and goggles, and keep children and pets away.
Deal with the damp first: fix roof leaks and ventilate the loft. Babergh District Council explains that attacks tend to continue until the timber dries out, and can take a while to stop afterwards.
Roof timbers and beams: the surveyor decides whether a timber needs strengthening or replacing, and whether treatment is needed and where. Treat only the active areas.
Old and listed buildings: drilling and spraying everything can damage historic timber. Treatment works on a listed building may need listed building consent: ask your council's conservation officer first.

What not to do

Spraying the whole loft 'just in case' because a few old holes were found during a house sale.
Spraying a wood treatment in a closed room or a bedroom.
Storing old furniture or reclaimed timber in the loft without checking it first.
Signing up on the spot after a cold call offering a 'free roof timber survey'.

Good to know

A watertight roof and a well-ventilated loft are the best protection: see Damp patch on a ceiling below the roof.
When you buy a home, a building survey by a qualified surveyor can point out woodworm. If you are selling, answer the seller's questions honestly; ask your conveyancer if you are unsure.
Wet rot and dry rot are fungi, not insects. They also come from damp, and dry rot needs professional advice quickly.

Tom buys a 1930s semi near Guildford. In the loft, he finds pale dust under a rafter and some oval holes. He vacuums it up and checks again three weeks later: there is fresh dust. An independent surveyor confirms house longhorn beetle in two rafters, finds a leak at the ridge, and specifies repairs and treatment for those areas only. Tom gets written quotes from two firms before choosing one.

A made-up story, for illustration.

Bobby

Sources, verification, confidence

Verified on 6 November 2026, for England. Confidence: high for how to tell the main beetles apart, the active-or-old checks and the role of damp; high that building regulations name areas at risk from house longhorn beetle (check table 1 or ask building control for your area); medium for listed building rules, which depend on your council. This guide describes common cases, not a diagnosis.