Woodworm treatment, and the hole that proves nothing

A flight hole is where a beetle got out, sometimes decades ago. What counts as evidence of a live infestation, which of the five UK beetles you are actually looking at, and why dry timber deals with most of this for nothing.

By The Damp GuyLast updated 11 September 2026

The short version

Holes are not evidence of anything happening now. Historic England states that the existence of insects' flight holes in structural timber or furniture does not necessarily mean the infestation is still live, and that where the problem is historic, treatment is not generally necessary. SPAB goes further: much beetle attack found in old buildings is extinct. Activity has to be shown, and you can start showing it yourself with a pencil and a sheet of paper. The other half is the water. Wood-boring insects only establish themselves where dampness exists, and Historic England puts the line at about 15 per cent timber moisture content, below which furniture beetles and death watch beetles will not thrive. A comfortable heated room holds timber at 8 to 12 per cent. Dry the timber and you have removed the conditions, which is the same answer this site gives about every other kind of damp.

Five beetles go by the name woodworm, and they mean different things

Start here, because the species decides how worried to be and what the evidence should look like. The hole size and the dust do most of the identifying.

The five UK wood-boring beetles compared by the timber they attack, the flight hole and frass they leave, and what finding each one usually means
Beetle	What it goes for	What it leaves behind	What finding it means
Common furniture beetleAnobium punctatum	Seasoned sapwood in both softwood and hardwood, usually avoiding the heartwood	Round, about 1.5mm, quoted elsewhere as 1 to 2mmGranular, like fine sand, gritty to the fingers	The one nearly every UK case turns out to be. The PCA calls it the most common wood destroying insect in UK buildings, and says most damage is in timber that has been in use for ten years or more
Death watch beetleXestobium rufovillosum	Decayed hardwood, oak above all. The PCA says timber free from decay is rarely if ever attacked	Round, about 3mm, and sometimes none at all because adults can emerge from cracksSmall bun-shaped pellets, easy to see	The serious one, and the one that tells you there is already fungal decay in the timber. Which? calls it quite rare in the north and in Scotland
House longhorn beetleHylotrupes bajulus	The sapwood of softwoods, and the PCA puts it in certain localities such as Surrey and West London	Often nothing obvious. The PCA says there is very little external evidence beyond an unevenness in the surface over the boringsRarely the clue, because the damage stays inside the timber	The only one the Building Regulations name. It can leave a roof timber as a thin veneer of sound wood, and its larval period in England averages six to seven years
Powder post beetleLyctus species	The starchy sapwood of new or recently dried hardwood, oak, ash, elm and sweet chestnut	Round, about 1.5mm, usually packed with dustFlour-fine, and a lot of it	A timber problem, not a house problem. The starch runs out after about ten to fifteen years, so the PCA says these beetles are never found in old wood, and the NHM says damage to structural timber is decorative and needs no treatment
Wood-boring weevilEuophryum confine and relatives	Damp and at least partially decayed timber only, often behind skirtings and in decaying wall plates	Not the tell. The adults leave characteristic channels, or striations, across the surfaceNot published in any source I could read	This site's whole argument in one insect. The PCA says weevils are normally brought under control by the measures taken to deal with the wet rot that let them in

Read down that last column and the picture changes shape. The common furniture beetle is what nearly every case turns out to be, and the PCA calls it the most common wood destroying insect in UK buildings. The powder post beetle is a timber-yard problem that arrives in the wood: the starch it feeds on runs out after ten to fifteen years, so the PCA says these beetles are never found in old wood, and the Natural History Museum says damage to structural timber is decorative and needs no treatment.

Two rows point straight back at water. Death watch beetle lays its eggs almost invariably in decayed parts of the timber, and the PCA says timber free from decay is rarely if ever attacked, so finding it means there is already fungal decay in that timber. The wood-boring weevil is the same story with the volume turned up: the PCA restricts it to damp and at least partially decayed timber, behind skirtings and in decaying wall plates, and says weevils are normally brought under control by the measures taken to deal with the wet rot itself.

A flight hole is an exit, and the burden of proof sits with the person quoting

The adult bores its way out and flies off. That is what the hole is, which is why a wall of them tells you a beetle was there and nothing about today.

Nobody disputes this, including the trade. The PCA's position is that before any treatment it is essential to establish if the infestation is active or historic, that it may have died out through unsuitability of the timber, decreased moisture content or previous treatments, and that in those cases treatment will not be justified. Its professional guidance is blunter: all timber should be investigated to determine evidence of current activity to justify any form of treatment.

The joint position statement written by RICS, Historic England and the PCA makes it a competency rather than an opinion. A surveyor should be able to recognise evidence of infestation by the commonly encountered wood-destroying insects, and take steps to determine whether the infestation is active. The same document governs a damp inspection, and it is worth holding any timber report against it.

So what does count as evidence. SPAB describes an active outbreak as holes with sharp rather than round edges, where the interiors and the bore dust are not dark but the colour of freshly cut timber. Homebuilding says the same in plainer words: fresh holes look clean and bright like newly sawn wood, old ones look dull with rounded edges. The PCA adds that frass piles are most obvious on vertical surfaces where the dust falls and leaves trails, and that one of the best indicators is the presence of adult beetle carcasses.

There is a false positive that gets people a treatment they did not need. SPAB records that active death watch infestation is sometimes reported in dry timbers where dust has been dislodged from old flight holes, perhaps by building work. Dust on the floor under a beam that has just had a floor lifted above it is not proof of anything.

Two tests you can run yourself. SPAB's is the stronger: where the signs are ambiguous, monitor for a year, covering a group of holes with acid-free tissue paper stuck down with water-soluble glue, which a beetle will punch through if one is in there. Wax polish plugged into the holes does the same job. Homebuilding's is easier: leave a sheet of paper under the timber between March and October and watch for new frass. Both work because emergence is seasonal. The PCA says adults can be found on window ledges from March to September, and for death watch beetle it recommends inspecting between April and June while they are emerging.

That season is also the answer to a question people do not think to ask. A survey in January cannot see a new hole or a fresh pile of dust, because there are none to see.

Woodworm is a damp problem wearing a different hat

Wood-boring insects, like timber-decaying fungi, only establish themselves where dampness exists. That one sentence from SPAB reorders everything that follows it.

Historic England gives the number. The moisture content of timber relates directly to the risk from wood-boring insects and fungal decay, and furniture beetles and death watch beetles will not thrive if it stays below about 15 per cent. It calls that acceptably dry. In the same document it says a room at 40 to 65 per cent relative humidity and around 20 degrees holds timber at an equilibrium moisture content of 8 to 12 per cent.

Put those two sentences next to each other and the shape of the problem changes. A heated, ventilated room is already well under the line. So an infestation in dry, sound timber is a population with nothing to eat comfortably and nowhere to go, and Historic England says the reverse too: an active furniture beetle infestation is itself evidence of an environment that is locally or comprehensively damp.

The trade says it as well, which is what makes it worth repeating. The PCA's code of practice states that all active fungal decay and most insect infestation result from excess moisture in the building, and that identifying and rectifying the causes of the dampness must be regarded as a fundamental part of a successful treatment. Historic England draws the conclusion: replacing the timber or applying a chemical without solving the source of damp treats the symptom and not the cause, and the problem is likely to recur.

Which means the first job is finding where the water comes from, not choosing a fluid. The usual suspects behind an infested floor or a wet wall plate are the ones this site covers elsewhere: a wall letting rain through, a bridged or failed damp proof course, blocked sub-floor vents, or a leak nobody has looked for. Sort the water and the same measures deal with rot in the same timbers, which is usually the more expensive half of the problem anyway.

One caution about the reading itself. Historic England warns that surface moisture content in a cold roof often exceeds 20 per cent in winter when the attic humidity approaches 90 per cent, and cites monitoring at Lincoln Cathedral where surface readings swung from 16 per cent in summer to 20 in winter while readings at depth stayed between 11 and 13, a range it calls safely dry. Its rule of thumb is useful: if a meter says the timber is dry then it probably is, but a damp reading may only be a transitory surface effect. SPAB adds that over-reliance should not be placed on surface readings at all, because surface deposits and past chemical treatments both throw them off. The same instrument has the same limits on a wall.

What a spray reaches, and what it cannot

A surface-applied insecticide does a real job. It is a narrower job than the quote usually implies, and the trade body publishes the limit itself.

Here is the PCA on treating death watch beetle, in its own guidance: treatment by brush or spray during the emergence period is useful in destroying eggs and young larvae before they enter the wood, but it is doubtful whether such treatment will kill older larvae working below the surface at any appreciable depth. Tim Hutton, writing in the Building Conservation Directory, puts the same point in millimetres. Insecticides applied retrospectively generally only penetrate a few millimetres below the surface, and may therefore not affect the larvae deep within the timber.

Which? states the consequence without flinching. The treatment will not penetrate through the depth of the timber, but the beetle has to emerge to reproduce, and it meets the treatment at that point. So a spray is a barrier on the way out and on the way back in. It works on the next generation, over seasons, and it does not stop what is already chewing through the middle of the joist.

That explains a line in the PCA guidance that reads oddly until you know it. For death watch beetle it recommends two applications between April and June, supplemented by targeted paste, and then further annual applications for at least four consecutive years. Four more years is not a sales tactic. It is what treating emerging adults actually involves.

The honest limits, all published by the trade. The PCA notes that where timbers are embedded in masonry, inaccessible, historically sensitive or very large, surface-applied chemicals struggle to control an infestation at all. Its code of practice says the limited value of surface preservative in the face of sustained damp conditions must be understood by the surveyor and the client. And where all surfaces cannot be inspected or treated, the code says the client should be told and the risk of continued infestation made clear, preferably in writing. That last one is a sentence worth asking for by name.

On spraying the whole roof. SPAB's own summary of this subject is that sound timbers and old woodworm holes are sprayed unnecessarily when a building changes hands, and that targeted treatment is appropriate but not as a substitute for promoting drying, nor as a general precaution for extinct or non-existent outbreaks merely to obtain a guarantee. It allows the exception plainly, where infestation is extensive, the timber lacks durability, or moisture cannot be cut far enough. Homebuilding says the practical version: if there is active woodworm in one beam, treat the affected area rather than every timber in the house. The PCA's code adds the part that surprises people, which is that a statutory duty exists to avoid unnecessary use of wood preservatives, and that where somebody else's specification calls for treating areas that appear free of infestation, it falls to the applicator to justify it.

Before anything is sprayed in a roof, ask about bats. All bat species and their breeding and resting places are protected by law, and damaging or destroying a roost is an offence, as is obstructing access to it or recklessly disturbing a bat in a place of shelter. Historic England is specific about the overlap: carry out a bat survey first, and treatments including bombs and fogging systems are harmful to bats exposed to them, which is a particular problem on roof timbers because bats often roost on the wood itself. Natural England publishes a list of timber-treatment chemicals suitable for use in or near bat roosts, and licences for unavoidable harm come from the same place. I cannot tell you what is in your loft. I can tell you the question has to be asked before the sprayer arrives.

And who is allowed to apply it. Wood preservatives are biocidal products, and HSE states that a product label says who may use it: members of the general public must not use professional or industrial use products. The PCA accepts that furniture and small wooden articles can be done by brush or hand spray with an amateur-approved product. A roof void is a different proposition.

The one place the regulations require treating timber in advance

Everything above is about existing timber. There is exactly one situation in England where the Building Regulations call for preventive treatment, and it is narrower than most people expect.

Approved Document A, the statutory guidance on structure, says this at section 2B2: in the geographical areas specified in Table 1, softwood timber for roof construction or fixed in the roof space, including ceiling joists within the void spaces of the roof, should be adequately treated to prevent infestation by the house longhorn beetle.

Table 1 is 8 entries long, and this is the whole of it.

In the Borough of Bracknell Forest the parishes of Sandhurst and Crowthorne.
The Borough of Elmbridge
In the District of Hart, the parishes of Hawley and Yateley
The District of Runnymede
The Borough of Spelthorne
The Borough of Surrey Heath
In the Borough of Rushmoor, the area of the former district of Farnborough
The Borough of Woking

That is the complete list, from the Approved Document A, "Structure", 2013 edition, and it is free to read in full. Note what it does not cover. It applies to new softwood for roof construction in those 8 areas, it names one species, and it says nothing at all about treating the timber already in your house, anywhere in the country. If a quote leans on the Building Regulations and your address is not on that list, the regulations it is leaning on are about something else.

The PCA describes house longhorn as restricted to certain localities such as Surrey and West London, with a larval period in England averaging six to seven years and sometimes running to eleven. It is also the hardest one to spot, which is why its row above has no hole size: the PCA says damage to a roof timber may be so extensive that only a thin outer veneer of sound wood is left, with very little external evidence beyond an unevenness in the surface where the borings run underneath.

What it costs, and why two guides cannot both be right

Neither of these sources is independent. Both make money when the enquiry turns into a job, so the figures are attributed to whoever published them and never blended into one range.

Published UK woodworm treatment costs from two cost guides, attributed per source and not averaged
The job	MyJobQuote	HomeHow
A woodworm survey	£80 to £250	£80 to £250
Treating a whole house	£750	£500 to £1,000
Treating a 25 square metre loft	£800 to £1,000	not published
Labour, per hour	£40 to £70	£20 to £40

Look at rows two and three together. One guide prices a 25 square metre loft above the floor of what the other charges to treat an entire house for every stage of woodworm. Both were read on the same day. They cannot both be describing the same market, and the likeliest reason is that they are quietly assuming different methods.

Which is the more useful finding, because it sits inside one source. MyJobQuote prices the same 25 square metres at £150 to £200 by boron treatment and £700 to £800 by fumigation or fogging. Method moves the number roughly four-fold, further than property size or region do. Its regional uplift is 10 to 20 per cent for London and the South East, and its whole-house average is around £750 for a job taking one to three days. A headline woodworm price that does not name the method has told you nothing you can use.

The survey row is the one to sit with. Both guides price a woodworm survey at £80 to £250. The treatment contractors advertise the survey at no charge. That gap is not a pricing error, it is the business model showing through, and it works exactly the same way on the damp side of the report. A survey with no fee attached is paid for by the work it specifies. That is not an accusation and it does not make the findings wrong. It means the inspection is not independent of the outcome, which is a different thing and a fact you can check.

One more number worth holding, because it is the one most likely to be missing from your quote. MyJobQuote puts floorboard repair and replacement at £200 to £800 separately from the treatment. Making good is routinely the larger half of a damp or timber bill, and it is the part that gets quoted last.

The guarantee, and the question nobody asks about it

A long guarantee reads like confidence. What it is actually worth depends on two things that almost nobody publishes.

I read 4 sources that publish a guarantee period on woodworm work. Here is what each of them says, and what each of them leaves out.

Timberwise publishes a 20 year guarantee on all completed timber treatments. Silent on whether it is insurance-backed, what it excludes, and whether it transfers to a buyer.
Prokil publishes a guarantee for up to 20 years. Silent on what "up to" depends on, the scope, the exclusions and the backing.
Advanced Damp publishes a 10 year guarantee, transferable on sale and accepted by solicitors and lenders. Silent on whether it is insurance-backed, and what happens to it if the company stops trading.
MyJobQuote, describing the market publishes some firms give 10 to 30 year guarantees, and longer cover usually means a higher price. Silent on which firms, and on what backing. No source read published a 30 year guarantee of its own.

Not one of them states what backs it. That absence is the answer to the question, and it is the first thing to ask about in writing.

The PCA explains the difference clearly, in its own words about its own members. A company guarantee obliges the company to put defects right during the period, usually no longer than ten years. An insurance-backed guarantee is the one that pays out where the contractor has ceased to trade and cannot meet its obligations. Without that, a thirty-year promise lasts exactly as long as the company does. The PCA also notes two things a claimant discovers late: a fee for the investigating survey is usually payable, and disputes arise when the contractor says the defect falls outside the scope.

A guarantee can also be voided by something you did not do. The PCA's code of practice requires a report to state clearly any repair and maintenance items which, if omitted, will compromise the property or invalidate the guarantee. If the damp that fed the infestation is still arriving, that clause is where the claim goes to die.

Then there is the question of what a guarantee against a dead infestation is worth at all. SPAB's position is that treatment should not be applied as a general precaution for extinct or non-existent outbreaks merely to obtain a guarantee. The PCA has published a case of its own that makes the point harder than SPAB does: a contractor recommended only a surface application to exposed timber, which the owner worked out would most likely be very ineffective, and had offered a 20 year guarantee on what the PCA calls a very limited and poorly conceived treatment programme. A long guarantee on work that was never going to be tested costs the firm giving it nothing.

What to ask before you agree to anything

You are about to have a conversation you are not equipped for. These questions are the ones the published standards already entitle you to ask.

Which timbers show ACTIVE infestation, and on what evidence? Not which timbers have holes. The joint position statement makes determining activity a competency, so asking for it in the report is asking for the standard to be met.
What species, and what did you see that identified it? The PCA's own diagnostic order is identify the insect, then establish that the infestation is active and needs action. Death watch beetle and a powder post beetle in a floor mean two completely different jobs.
What were the timber moisture readings, at the surface and at depth? Historic England's threshold is about 15 per cent, and it warns that a winter surface reading in a roof can mislead while the timber at depth is safely dry.
Where is the water coming from, and what deals with that? The PCA's code of practice calls rectifying the cause of the dampness a fundamental part of a successful treatment. A specification that never mentions the water is treating the symptom.
Which surfaces cannot be inspected or treated, and what is the risk? The code says that where they cannot, the client should be told and the risk of continued infestation made clear, preferably in writing. Ask for the writing.
Has a bat survey been done? Roosts are protected and roof timbers are where bats sit. This one is not optional.
Is the guarantee insurance-backed, and what invalidates it? A company guarantee ends with the company, and the insurance behind one has a published trigger and published exclusions. Get the answer in writing alongside the list of maintenance items that would void it.
Would you, or anyone connected to you, quote for the work you recommend? The joint position statement says any conflicts of interest should be clearly stated in the report, and that a remedy benefiting the surveyor's firm financially must be declared. SPAB's own advice is to take the opinion from an independent chartered surveyor or consultant rather than a remedial treatment contractor.

About this resource

The weight here is carried by four documents, all published by bodies that sell no treatment: Historic England's "Assessing damp in historic buildings", June 2026 edition, and its guidance on timber treatments and bats; SPAB's advice on wood-boring insects; and Approved Document A, quoted from the 2013 edition and extracted from the published PDF. The species detail and most of the honest limits on treatment come from the Property Care Association's own guidance note and code of practice, which matters because the PCA is the trade body for the firms doing the work. The costs are published ranges from two commercially interested guides, read on 11 September 2026, attributed separately and never averaged. They are not a quote.

Two things this page does not have. There is no figure for what proportion of flight holes in UK houses are historic, because no source supports one, and no hole size for house longhorn beetle, because the figures in circulation come only from pages selling the cure. Nothing here calls any company dishonest and no company is named. The point is who benefits from an answer, which you can check, rather than anyone's character, which you cannot. This site does not survey, treat, quote or refer, takes no fee from anyone who does, and cannot tell you what is happening in your timber.

Common questions

How to tell if a woodworm is still alive?

You look at the edges of the holes and the colour of the dust, and then you wait. SPAB puts it plainly: active outbreaks show holes with sharp rather than round edges, and the bore dust and the inside of the hole are the colour of freshly cut timber rather than dark. Where the signs are ambiguous, SPAB says monitor for a year, covering a group of holes with acid-free tissue paper stuck down with water-soluble glue, which an emerging beetle punches through. Wax polish in the holes does the same job. One warning that almost nobody prints: SPAB notes that dust dislodged from old flight holes, perhaps by building work, gets reported as an active infestation.

Should I panic if I find woodworm in my floorboards?

No, and the reason is that you have found holes rather than beetles. Historic England states that the existence of flight holes in structural timber or furniture does not necessarily mean the infestation is still live, and that if the problem is historic then treatment is not generally necessary. Homebuilding puts the consequence bluntly: unless serious structural damage has already been done, inactive woodworm is completely harmless. So the job in front of you is evidence, not a quote. Mark the holes, look for fresh dust through the spring and summer, and find out what the timber moisture content is.

Does woodworm ever go away?

It can, and the mechanism is the moisture rather than a chemical. The Property Care Association says an infestation may already have died out through unsuitability of the timber, decreased moisture content or previous treatments, and that in those cases treatment is not justified. Historic England gives the number that makes it real: furniture beetles and death watch beetles will not thrive below about 15 per cent timber moisture content, and a room at 40 to 65 per cent relative humidity holds timber at 8 to 12 per cent. SPAB is blunter still, saying much beetle attack found in old buildings is extinct.

What time of year do woodworms fly?

Spring and summer, and it decides when you can gather evidence at all. The PCA says that from March to September adults can be found on the window ledges of houses containing infested timber, and for death watch beetle it advises that inspection should if possible happen between April and June while the beetles are emerging. The Natural History Museum says furniture beetles emerge in early summer and live two to four weeks. Which? gives the general season as March to October. Outside that window there are no new holes and no fresh dust to find, which is worth knowing before you agree to a survey in January.

Can I do woodworm treatment myself?

Sometimes, and the limit is set by law rather than by skill. HSE states that a biocidal product label says who may use it, and that members of the general public must not use professional or industrial use products. Wood preservatives are biocidal products and have to be authorised before they can be sold. The PCA accepts that furniture and small wooden articles can be treated by brush or hand spray with an amateur-approved product. The harder question is not who holds the brush. It is what a surface application reaches, and the PCA itself doubts that it kills older larvae working below the surface at any appreciable depth.

Is there a guarantee that woodworm treatment will work?

There are guarantees, and the length of one tells you very little. Of the four sources I read that publish a period, none states what backs it. The PCA explains the difference: a company guarantee is only as good as the company, while an insurance-backed guarantee pays out where the contractor has ceased trading. It also notes a fee is usually payable for the survey that investigates a claim, and that disputes arise over what falls inside the scope. SPAB makes the sharper point, that treatment should not be applied as a general precaution for extinct or non-existent outbreaks merely to obtain a guarantee.

Can I sell a house with woodworm?

Yes, and the practical problem is the survey rather than the sale. A buyer's surveyor who sees flight holes will flag them, and a flag is a recommendation to investigate rather than a diagnosis. The useful thing a seller can hold is evidence of what the timber is doing now: a moisture reading, marked holes that produced nothing through a summer, or a report from somebody who is not tendering for the work. Worth knowing separately that at least one insurer, AXA, states plainly that its home insurance does not cover woodworm damage, so this is not a claim you can pass along.