Borer treatment
Borer treatment in Auckland, starting with whether it is still active
Borer calls reach us in three ways: a builder's or building inspector's report on a house you are about to buy, a ceiling hatch opened during a renovation that shows a roof space peppered with small holes, or a little heap of fine dust under a rimu sideboard or a doorframe in early summer. Each of them raises the same question, and the honest answer is often that the borer moved out decades ago.
Ask about borer
Tell us what you have noticed and we will put a price in writing.
Monday to Friday 7.30am–6pm, Saturday 8am–2pm. Urgent wasp work is prioritised.
Borer in an Auckland house: the short answer
Most borer holes in an Auckland house are older than the people living in it. The common house borer, Anobium punctatum, spends three to four years inside the sapwood of untreated timber before it chews out through a round hole of one to two millimetres, so the questions that decide the treatment are which beetle made the holes, whether any are still emerging, and whether the timber is bare or finished.
We price borer work only after we have established two things, which beetle made the damage and whether it is still alive. Treating timber that has been quiet since before the house was last reroofed is money spent for nothing, and we will tell you so in writing. Where the infestation is live, the method then depends on whether the timber is bare, like roof framing and subfloor bearers, or painted, varnished and finished, like skirtings, doors and furniture.
Which borer made the holes, and what each one looks like
Four beetles account for nearly everything we find in Auckland timber, and the exit hole and the bore dust identify them better than the beetle does. Round 1–2 mm holes with gritty dust mean common house borer. Oval holes 3–7 mm long with packed dust mean two-toothed longhorn. Pinhead holes and talc-fine dust in hardwood mean powderpost beetle. Holes of 10–20 mm mean huhu, and damp timber. The table below has the detail.
The common house borer is the one that matters most. It came from Europe, it is found throughout New Zealand, and the Scion leaflet published by the NZ Farm Forestry Association holds it responsible for "most of the insect damage found in structural and decorative timber" here. Its larvae feed mainly in sapwood, the paler outer band of a board, and the adults are small brown beetles of about 3–4 mm that live for a few weeks in early summer.
The two-toothed longhorn, Ambeodontus tristis, is a native beetle whose larvae work in the heartwood too, not only the sapwood, which is why its damage stays hidden until the timber is opened up. It favours rimu, kahikatea and macrocarpa, and in houses it turns up in subfloor bearers and joists in damp, poorly ventilated places. The powderpost beetle, Lyctus brunneus, attacks only the starchy sapwood of hardwoods such as tawa, rewarewa, oak and ash, so it shows up in flooring and furniture rather than in framing. A huhu grub in house timber is a moisture finding before it is a borer finding.
How serious is borer in a house?
Usually less serious than it looks. Common house borer feeds mainly in sapwood, so a scatter of holes along the edge of a rafter or a floorboard normally leaves the heartwood that carries the load intact. It becomes a structural matter when an infestation has been reinfesting the same members for many years, or when the two-toothed longhorn is working in damp subfloor timbers, where untreated rimu bearers and joists are recorded as often severely damaged.
There are signs that call for a builder or a building surveyor rather than for us: edges that crumble when you press them with a thumbnail, timber that dents easily, a floor that has started to feel springy, and longhorn holes in bearers. We will record what we see and say plainly when it needs one of them. We do not carry out structural repairs, and we will not suggest that a treatment puts weakened timber right.
Before any of that, the first question is whether the borer is still there at all, and in older houses the answer is often no. We have set out how to tell whether borer is still active from the dust and the hole edges, with a simple way to check over one summer.
What kills borer, and why the timing matters
The larvae are the problem, and they are inside the timber, out of reach of almost anything sprayed onto the surface. What works is a residual insecticide or a boron-based preservative applied to bare timber. It kills each beetle as it chews its way out and each newly hatched larva as it tries to bore in, and because it lasts longer than the life cycle, the population simply runs out over the following seasons.
Borate products soak into unfinished wood and can reach larvae close to the surface, but neither they nor a residual spray will pass through paint, varnish or polish. On finished timber the flight holes themselves are injected, one by one, which reaches the tunnels behind them. Timing matters as well: the common house borer flies mainly from November to January, and the longhorn in autumn, so the work is best done before the adults emerge.
Aerosol foggers sold as borer bombs only reach adult beetles that happen to be in the air or on a surface during the few hours the fog lasts. That is why we use one in a roof space only as an addition during the flight season, never as the treatment itself. If you are weighing up doing it yourself, we have described what borer bombs and sprays from the hardware store can reach, product by product.
Why older Auckland houses carry most of it
Borer needs untreated timber, and Auckland has a great deal of it. Boron treatment of building timber only began in 1952, so villas and most pre-war bungalows were framed and floored in untreated native timber and early radiata pine. Untreated kiln-dried framing was allowed again from 1995 until treated timber became a requirement for consents issued from April 2004. Boron-treated framing is not what borer infests.
In a villa or bungalow we look first at the roof framing and sarking, the subfloor bearers and joists, the backs of skirtings and the floorboards near a damp corner. Moisture decides a great deal: the common house borer develops fastest in humid conditions, so a subfloor that is damp and badly ventilated is where an infestation keeps going longest, and better ventilation is part of the fix rather than an extra.
Renovation timber tells its own story. Framing added in an extension or a reroof since the 1950s is usually treated while the original is not, which is why we so often see damage stop cleanly at a renovation line. Since 2011 the building rules have allowed H1.2 boron-treated radiata pine and Douglas fir framing in enclosed spaces, and timber treated that way is not where we find live borer.
Identification
Which borer made the holes
| Beetle | Timber it attacks | Bore dust | Adult size | Exit hole |
|---|---|---|---|---|
| Common house borer, Anobium punctatum | Sapwood of rimu, kahikatea and radiata pine, furniture | Loose and gritty between the fingers | 3–4 mm, brown | Round, 1–2 mm |
| Two-toothed longhorn, Ambeodontus tristis | Sapwood and heartwood of rimu, kahikatea and macrocarpa, often damp subfloors | Tightly packed scrapings and pellets | Up to 25 mm | Oval, 3–7 mm long |
| Powderpost beetle, Lyctus brunneus | Sapwood of hardwoods only: tawa, rewarewa, oak, ash, elm | Fine as talcum powder | 4–7 mm | Round, under 2 mm |
| Huhu beetle, Prionoplus reticularis | Damp or decaying wood, not sound dry framing | Packed pellets behind the grub | 40–50 mm, grub 50–70 mm | Oval, 10–20 mm |
How we do it
How a borer job runs, from inspection to the flight season
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We establish whether it is live
Pale fresh dust, clean edged holes and the time of year tell us whether anything is still emerging. Old damage on its own needs nothing, and we say so.
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We identify the beetle and the timber
Hole shape and size, the texture of the dust, whether the timber is bare or finished, and how damp the subfloor is.
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We price only the timber that needs it
Roof space, subfloor, interior joinery or furniture, itemised, rather than a whole house figure.
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We treat before the beetles fly
A residual or borate treatment on bare timber, holes injected where the timber is finished, timed ahead of the November to January flight.
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We tell you what to watch, and who to call
What fresh activity looks like next summer, and where timber is weakened, a referral to a builder rather than a repair we are not qualified to do.
Cost
What borer treatment costs in Auckland
| Job | What it covers | Indicative |
|---|---|---|
| Roof space treatment | Residual or borate treatment of bare roof framing, standard house | $350 – $690 |
| Subfloor treatment | Piles, bearers, joists and the underside of the flooring | $520 – $860 |
| Roof space and subfloor together | Typical three bedroom villa or bungalow | $920 – $1,500 |
| Furniture and finished interior timber | Flight holes injected, bare faces treated, before the flight season | from $250 |
Prices include GST. See the full pricing page for what moves a job within its range.
Questions
Borer treatment questions
How much does borer treatment cost in Auckland?
A roof space on its own is $350 to $690 and a subfloor on its own $520 to $860, while both together for a typical three bedroom villa or bungalow come to $920 to $1,500. Furniture and finished joinery start from $250. The figure moves with how much bare timber needs covering, how awkward the access is, and whether the longhorn is involved. If you only want an inspection, for example before buying, that is a timber pest inspection, listed on the pricing page at $250 to $350.
Can I treat borer myself?
For small, accessible jobs, yes: a piece of furniture, an exposed beam or a few boards, using a registered borer product on bare timber and an injector for holes in finished timber. A whole roof space or subfloor is much harder, because coverage, access and protective gear decide the result, and no product will tell you whether the borer was live in the first place.
When is the best time to treat borer?
Before the adults fly. For the common house borer that means getting a residual treatment onto bare timber by October or November, ahead of the November to January emergence; the two-toothed longhorn emerges in autumn and early winter. A residual treatment applied out of season still works when the beetles chew out later, so timing matters most for anything sprayed into the air.
Do borers eat treated timber?
Not boron-treated framing, which is the reason it is used. The exposure is in untreated timber: nearly all framing from before 1952, much of the native timber and early radiata pine in villas and bungalows, some untreated kiln-dried framing put in between 1995 and 2004, and old furniture. Where we find live borer in a newer house, it is almost always in a piece of untreated timber added later.
What is the best treatment for borer in New Zealand?
It depends on the timber rather than the brand. Bare timber takes a residual insecticide or a borate preservative that outlasts the life cycle. Painted or varnished timber is treated by injecting the flight holes. Badly weakened members are replaced by a builder with treated timber. Aerosol bombs only ever supplement those. Which of them is right turns on whether the borer is live and the timber bare.
Can borer in furniture spread into the house?
It can. The common house borer lays its eggs on bare timber and in old flight holes, so a live infestation in an unfinished chest of drawers or an old pine table is a source for anything untreated nearby, while most polished or painted furniture is protected by its finish. Check second-hand pieces before they come inside, and see our guide to treating borer in furniture.
What if the damage is termites, not borer?
Occasionally. Termites leave no rows of round exit holes, and the native drywood termite pushes out hard pellets that are six-sided in cross-section rather than gritty dust. If anything looks like termites in building timber or imported furniture, do not spray or disturb it, and report it to MPI on 0800 80 99 66. We have explained how to tell borer from termites in more detail.
I found huhu grubs in timber. Is that borer?
Not in the usual sense. Huhu grubs, which grow to 50–70 mm, only develop in damp or decaying wood, so in a house they point to a moisture problem such as a leak, a wet subfloor or a rotting deck joist. Fix the moisture and have the rotten timber replaced; a borer treatment is not the answer. In firewood or a dead tree, huhu are simply part of normal decay.
Guides
Borer guides: activity, DIY products, furniture, termites
Is the borer in your house still active?
Most older Auckland houses have borer holes. How to tell live borer from old damage by the dust and the hole edges, and what it means if you are buying one.
Read this DIY treatmentTreating borer yourself, and what each product actually reaches
What borer bombs, surface sprays, hole injectors and home remedies such as vinegar or kerosene can reach inside timber, and when treating borer yourself is enough.
Read this FurnitureBorer in furniture, and how to keep the piece
How to tell whether borer in a chair, dresser or antique is still active, which beetle made the holes, and how injection, freezing and refinishing deal with it.
Read this Timber pestsBorer or termites?
Borer and termites both hollow out timber, but the dust, the holes and the next step differ. How to tell them apart in a New Zealand house, and when to call MPI.
Read thisDealing with borer?
Describe what you have seen, or send a photograph. We will tell you what it is and what it needs before anyone visits.