How Long Does Woodworm Treatment Last?

It is the question almost every homeowner asks once the work is booked: having paid to deal with woodworm, how long until I have to worry about it again? The reassuring answer is that done properly, a professional treatment protects the timber for decades — and a good firm will put that in writing with a 30-year guarantee. But a guarantee is only as good as what it covers and what you do afterwards, so it pays to understand exactly what you are getting.

This guide explains how long treatment realistically lasts, what the 30-year guarantee does and does not cover, and the handful of practical things that decide whether woodworm stays gone for good.

What “lasting” actually means

It helps to be clear about what a treatment is doing. A professional insecticidal treatment leaves a protective residue in and on the timber. When beetle larvae feed on treated wood, or adult beetles try to lay eggs on it, the residual treatment kills them — breaking the lifecycle so the infestation cannot continue.

Most UK cases are the common furniture beetle (Anobium punctatum), which runs a 3–4 year lifecycle. Much of that life is spent invisibly, as larvae tunnelling inside the wood. This is why you should not judge a treatment by the next few weeks. You may still see a few adult beetles emerge in the first emergence season after treatment — they were already inside the timber, near the surface, ready to come out. That is expected and is not a sign of failure. The real test is whether new activity continues over the following seasons, and a correctly treated, dry timber should show none.

How long a professional treatment lasts

For a standard water-based permethrin treatment of accessible timber, the protective residue remains effective in the wood for many years — comfortably long enough to see out the beetle’s lifecycle and well beyond. For deeper structural work, boron paste and gel penetrate further into the timber and stay active inside it, which is why they are used on joist ends and heavier beams.

In plain terms: once the timber is dry and correctly treated, you should not expect the same infestation to return. Reputable treatments are not a temporary fix you repeat every couple of years. They are designed to deal with the problem once.

What shortens the life of a treatment is almost always moisture and disturbance:

• New or recurring damp can re-wet timber, encourage decay, and create fresh conditions for beetles.
• Stripping, sanding or replacing treated timber removes the protected layer.
• Adding new, untreated timber (a loft conversion, new joists, reclaimed wood) brings in wood that was never protected — and occasionally its own beetle.

Address those and a single professional treatment genuinely lasts. The full picture of what goes into doing it right is covered in our complete guide to treating woodworm.

What the 30-year guarantee covers

The headline reassurance most homeowners want is the guarantee. A 30-year guarantee on treated timber is standard from a serious firm, and it matters for two reasons: it backs the quality of the work, and it is a document buyers and mortgage surveyors like to see when a property changes hands.

Here is what a typical guarantee does and does not do.

What it covers:

• The specific timber that was treated, against re-infestation by wood-boring beetle, for the guarantee period.
• A written treatment certificate confirming what was done, where, and with which products — the paperwork that satisfies surveyors and supports a sale.
• A return visit and re-treatment of the covered timber if live activity reappears in the treated areas within the term.

What it generally does not cover:

• Untreated timber. Only the areas inspected and treated are guaranteed. If only the loft was done, the guarantee does not extend to floors that were never surveyed.
• New damp problems. If a leak or rising damp later re-wets the timber, that is a building-maintenance issue. Most guarantees ask you to keep the property reasonably dry and address damp promptly. This is exactly why woodworm is so often treated alongside the damp that caused it.
• A different species or a fresh infestation in new wood. Guarantees relate to the treated infestation, not to timber introduced afterwards.
• Transfer rules. Many guarantees are transferable to a new owner, sometimes with a small administrative step. Check the terms if you plan to sell.

Always read your own certificate — terms vary between firms. The principle is consistent: treat it well, keep it dry, and the cover holds for decades.

Why the survey matters for how long it lasts

The single biggest factor in whether treatment lasts is whether the right problem was treated in the first place. That is decided at the survey, not the spray.

A proper woodworm survey does three things that protect the longevity of the work. It confirms the infestation is genuinely active (treating long-dead, historic woodworm is wasted money — and a clue that something was missed). It identifies the species, because a death watch beetle in old oak or a damp-loving wood-boring weevil needs a different approach to the common furniture beetle. And it finds the moisture source, because beetles thrive in damp timber and no insecticide will keep them away if the wood stays wet.

Skip the survey and treat the surface only, and you can get a brief reprieve followed by a return. Survey properly, fix the damp, treat the right timber with the right product, and the result holds.

How to stop woodworm coming back

Treatment kills the current infestation; these habits keep your home from becoming attractive to the next one. The common thread is keeping timber dry and watching for early signs.

• Control moisture. Keep timber below the moisture content that beetles favour. Fix leaks, gutters and penetrating damp quickly, and improve sub-floor and loft ventilation. Damp timber is the root cause of most repeat problems.
• Ventilate sub-floors and lofts. Clear airbricks and make sure roof spaces breathe. Stagnant, humid voids are where infestations quietly build.
• Inspect once a year. A five-minute look at floor joists, loft rafters and the backs of cupboards each spring lets you catch any fresh, pale frass or crisp new holes early. Knowing how to tell new activity from old is the whole game — our guide to active vs historic woodworm shows you exactly what to look for.
• Be careful with reclaimed and second-hand timber. Old beams, salvaged floorboards and junk-shop furniture can carry live beetle into a clean house. Inspect, and treat before installing.
• Keep your paperwork. File the certificate and guarantee somewhere safe; you will want them at sale time.

For a sense of what re-treatment or fresh work would cost if you ever did need it, our 2026 cost guide breaks down prices by room, roof and whole house — though with a guarantee in place, covered re-treatment should not fall to you.

The bottom line

A correctly applied professional woodworm treatment is built to last decades, not months, and a 30-year guarantee backs that up — covering the treated timber against re-infestation, provided you keep the property reasonably dry. The work lasts when the survey was thorough, the damp was fixed, and the right timber was treated. Keep an eye out once a year, deal with moisture promptly, and the same woodworm should not trouble you again.

Can woodworm come back after treatment?

Yes — but it is uncommon when treatment is done correctly. Professional permethrin spray leaves a residual insecticide in the timber that kills larvae and emerging adults for several years. The 30-year guarantee covers re-infestation of treated timber during that period.

However, there are scenarios where woodworm can return:

Adjacent untreated timber — If only part of a floor or roof was treated, beetles from untreated areas can colonise treated timber once the residual insecticide fades. A thorough treatment covers all at-risk timber, not just visibly infested sections.

New timber introduced after treatment — Bringing in second-hand furniture, reclaimed floorboards or unseasoned timber from an infested source introduces fresh beetles. Always inspect new timber before it enters a treated property.

Underlying damp not resolved — Woodworm thrives in damp conditions. If the moisture problem that encouraged the original infestation is not fixed, new beetles are more likely to settle. Treatment alongside damp-proofing gives the best long-term result.

If you see fresh holes or frass in previously treated timber within the guarantee period, contact your treatment company — re-treatment is covered.

How to prevent woodworm after treatment

The best prevention is keeping timber dry and well-ventilated:

• Maintain sub-floor ventilation — Ensure air bricks are clear and unblocked. A dry sub-floor void is far less attractive to wood-boring beetle.
• Check roof ventilation — Loft spaces should breathe. Blocked eaves or insufficient ridge ventilation keeps timber damp.
• Paint or varnish bare timber — Adult beetles need to access raw timber grain to lay eggs. Finished surfaces — painted, varnished or wax-treated — make it harder.
• Inspect annually — A quick check in summer (June–August) when beetles are active is all you need. Look for fresh frass or new holes in known risk areas.
• Treat replacement timber before fitting — Any new joists, rafters or floorboards going into an older property should be pre-treated with a permethrin or boron solution before installation.

Read our woodworm survey guide for what a qualified surveyor checks during a follow-up inspection.

Get professional help

Want treatment that comes with a written certificate and a 30-year guarantee, and a survey that gets the diagnosis right the first time? Get a free quote and a qualified surveyor will assess your timber, confirm whether it is active, and set out exactly what is covered.