Borer treatment
Treating live borer, area by area
Treatment starts from a finding, not from a product. Once a borer inspection has named the beetle, shown that it is still emerging and mapped the timbers it is in, each part of the house can get the method that suits it, timed to that beetle's season.
Wood borer treatment after a live finding means applying a residual or borate product to bare timber in the roof space and subfloor, injecting exit holes in finished timber such as floors and furniture, fixing the damp that keeps borer going, and checking again after the next flight season. Foggers are at most an extra for adult beetles in roof spaces. Timber that has lost strength goes to a builder.
Published Auckland prices run about $350–$600 + GST for a roof space and about $450–$750 + GST for a subfloor, a guide only.
What happens after an inspection finds live borer?
The findings become a plan, area by area. Bare framing in the roof space and subfloor gets a product that soaks into the timber, finished timber gets injection, anything too weak to keep goes to a builder, and moisture problems go on the list to fix. Timber the findings show as historic or inactive needs no treatment, and the quote covers only the work the findings support.
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Findings
Species, activity, timbers and moisture recorded for each part of the house.
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Plan
A method for each area, and any structural damage flagged for a builder.
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Moisture
Vents, leaks and wet ground dealt with, because damp timber keeps borer going.
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Treatment
Applied ahead of the beetle's emergence season.
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Follow-up
Marked areas checked for new holes and dust after the next flight season.
Which products treat borer in bare timber?
Residual surface treatments and borate preparations are the two main product types for bare timber. Consumer NZ describes a residual surface application on bare timber as the only long-term borer treatment. Borate products use boron compounds, the same family of preservative used in H1.2 framing, which BRANZ notes has a long record of protecting timber against insects and decay. Both need bare, unsealed wood.
In most Auckland houses that means rafters and sarking in the roof space, and piles, bearers, joists and the underside of floorboards in the subfloor. BRANZ also notes that boron is water-soluble and can leach from timber kept wet over long spells, one more reason the moisture fix belongs in the same plan. Product choice and application follow the label of the product used.
How is borer treated in finished timber?
Polished floors, painted joinery and furniture are sealed, so surface products cannot soak in. The usual method is to inject a borer product into the exit holes, which carries it into the tunnels behind the finish, and to treat whatever bare timber the same items have, such as the underside of the floorboards or the backs of furniture. Kiwicare's technical guidance names injecting flight holes as one way to reach larvae.
Part-by-part detail is in borer in floorboards, borer in weatherboards and borer in furniture and antiques.
Do borer bombs and foggers work as treatment?
Only against adult beetles. Consumer NZ notes that bombs, misting and fogging kill adults in flight but do not stop larvae feeding inside the timber, and Kiwicare positions its own fogger as a knock-down for adults between October and March. In a roof space during the flight season, a fogger can cut the number of adults laying eggs, alongside a residual treatment of the bare timber and never instead of it.
Retail borer products, foggers included, need no licence to buy or use. The borer bombs and sprays guide covers what each type reaches and where it fits.
When is the best time to treat borer?
Before the beetle's next emergence. The common house borer emerges mostly between November and January, sometimes from October and into March, so treating bare timber in winter or early spring puts the product in place ahead of it. The two-toothed longhorn comes out in autumn and early winter, so a longhorn finding is ideally treated before autumn. Larvae are in the timber all year, so a live finding need not wait for the season.
| Beetle | Adults emerge | Treat ahead of it |
|---|---|---|
| Common house borer | November–January, sometimes October–March | Winter to early spring |
| Two-toothed longhorn | Autumn to early winter | Summer |
| Huhu | November to early March | Fix the moisture first; the wet timber is the problem |
| Powderpost beetle | Usually October and November (NZFFA) | Before October; about a one-year cycle |
Month by month detail is in when borer fly in New Zealand.
Is whole-house fumigation used for borer in New Zealand?
Not as standard practice. Tenting a whole house and filling it with gas, which is common for some pests overseas, is not how borer is dealt with in New Zealand homes. Consumer NZ notes fumigation is not usually suitable for houses because the space has to be completely sealed, and nothing stays in the wood afterwards to stop a fresh attack. Fumigants are also controlled substances, limited to holders of a WorkSafe licence.
Products sold as borer "fumigators" for home use are aerosol foggers, not gas fumigation, and they reach only the adult beetles in the air.
Who can apply borer treatments in New Zealand?
Homeowners can buy and use retail borer products without a licence, as long as they follow the label. Commercial pest work is treated differently: under hazardous substances rules amended in 2020, a contractor using certain substances in urban pest management must hold the New Zealand Certificate in Pest Operations (Level 3) or another listed qualification. Which rules apply depends on the product used.
It is reasonable to ask whoever quotes the treatment which products they plan to use in each area and why. A plan that names a method for each part of the house is easier to check than a single price for "borer treatment".
How do you know the borer treatment worked?
By looking again after the next flight season. Treatment does not remove holes that are already there, so success shows as no new holes and no fresh dust in the treated areas over the following summer. Clean the dust from a few marked spots after treatment, photograph them, and check again in late summer. New holes through treated or filled areas mean a follow-up visit.
Results also depend on the damp being fixed. The common house borer develops fastest above about 70% relative humidity, so a subfloor that stays wet keeps conditions in its favour whatever product was used.
Questions people ask
What is the most effective way to deal with wood borer?
Match the method to the timber. Bare framing in roof spaces and subfloors takes a residual or borate surface treatment, finished timber takes injection into the exit holes, and timber that has lost strength is replaced. Damp is fixed at the same time, and the work is timed before the beetle's emergence. Foggers alone reach only adult beetles, not the larvae doing the damage.
Can you treat borer yourself?
Yes, within limits. Retail products need no licence, and injecting holes or brushing a product onto bare timber is practical for a small area you can reach, following the label. Roof spaces and subfloors are harder: they are cramped, the coverage has to be thorough, and what decides the job is whether anything is alive and the timber still strong, which a product cannot answer.
How much does wood borer treatment cost in Auckland?
Published Auckland prices put roof space treatment at about $350–$600 + GST and subfloor treatment at about $450–$750 + GST, with prices moving on access, size and how much finished timber needs injecting. These are a guide only, not quotes. The borer cost page sets out what moves the price and how the inspection fits in.
Does treatment repair borer damage?
No. Treatment stops further feeding; it does not put back the timber the larvae have eaten. Boards, joists or bearers that are soft or crumbling stay weak after treatment and need a builder. Borer damage repair explains when that work needs a building consent and how it fits with treatment.
Does boron-treated framing need borer treatment?
Usually not. H1.2 framing is treated with boron to resist borer, and BRANZ notes boric treatment has a long record against insects. It is not borer-proof in every condition: boron can leach from timber that stays wet for long periods. Untreated timber in the same house, such as older floorboards or furniture, can still carry borer.
Before you book treatment
- Borer costPublished Auckland prices for borer inspections and treatment, and what moves them
- Flight seasonThe months each borer flies in New Zealand, and what that means for treatment and for buyers
- Borer bombs and spraysWhat foggers, surface sprays, injectors and borate products each reach, and when DIY is enough
- Borer damage repairWhen borer damage needs a builder, which repairs are exempt from consent, re-piling and the order of work