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Borer inspection

Borer inspection for Auckland houses

Holes in a floorboard, a line in a building report, a little heap of dust under the stairs: each one raises the same set of questions, and an inspection is how they get answered for one particular house rather than houses in general.

A borer inspection is a close look at the timber in a house for wood-boring beetles and the damage they leave. The inspector identifies the beetle from its exit holes and dust, judges whether it is still emerging, records which timbers carry it, checks moisture, and says plainly when weakened timber needs a builder rather than treatment.

The inspection costs $285 + GST. The fee is credited against the treatment if you go ahead with the recommended work through the same operator.

What does a borer inspection check?

An inspection works through every part of the house where untreated timber can be reached safely: the roof space, the subfloor, the exterior cladding, and interior joinery and furniture you point out. In each area the inspector is answering five questions in the same order, so the findings can be compared room by room and read later by someone who was not there.

  • Which beetle. The shape and size of the exit holes and the texture of the dust identify it more reliably than a beetle found on a sill.
  • Live or historic. Clean, pale hole edges and fresh dust that reappears after cleaning point to emergence; dark, weathered holes with no new dust usually do not.
  • Which timbers. Sapwood edges of rimu, kahikatea and radiata pine are the usual targets of the common house borer. Untreated framing is what matters, not boron-treated framing.
  • Moisture. Damp subfloors and blocked vents keep infestations going and are part of the fix.
  • Strength. Timber that crumbles or dents under a probe is recorded as a builder's matter, not a treatment.

Which borer is it? Reading the exit holes

Four beetles account for most of what turns up in Auckland timber, and their exit holes differ enough to tell them apart. Round holes of one to two millimetres with gritty dust mean the common house borer. Oval holes of three to seven millimetres point to the native two-toothed longhorn. Pinhead holes in hardwood mean powderpost beetle, and large oval holes mean huhu in damp wood.

Exit-hole size guide for four New Zealand wood-boring beetles Holes drawn at six times life size beside a millimetre scale: powderpost 0.8 to 1.6 mm round, common house borer 1 to 2 mm round, two-toothed longhorn oval 3 to 7 mm long, huhu oval 10 to 20 mm. Exit holes at 6× life size 0 10 20 mm Powderpost beetle Lyctus brunneus talc-fine dust, hardwood only smallest largest round, 0.8–1.6 mm Common house borer Anobium punctatum gritty dust, sapwood smallest largest round, 1–2 mm Two-toothed longhorn Ambeodontus tristis packed dust, reaches heartwood smallest largest oval, 3–7 mm long Huhu beetle Prionoplus reticularis damp or decaying wood smallest largest oval, 10–20 mm Source: NZFFA Forest and Timber Insects in New Zealand leaflets. Hole sizes vary; use with the dust and the timber type.
Exit holes at six times life size. Hole size alone is not proof: the dust and the timber type are read with it.

The distinction matters for what happens next. The common house borer feeds mainly in sapwood, so a scatter of holes along the edge of a joist often leaves the heartwood carrying the load. The two-toothed longhorn tunnels through heartwood as well and is described by the NZ Farm Forestry Association as hiding its damage until the timber is opened. Huhu larvae need wood that stays damp, so huhu in a house is first a moisture finding. More on the native beetle is in the guide to the two-toothed longhorn.

Is the borer still active, or is the damage old?

Many Auckland houses carry holes made long before their current owners arrived, so activity is the line on the finding that changes the recommendation most. Fresh signs are pale, clean-edged holes, fine dust that gathers again after you vacuum it, and beetles appearing between November and January, when the common house borer emerges according to the NZ Farm Forestry Association.

Historic holes with nothing emerging are recorded as needing no work. Where the evidence is unclear, for example in a roof space that has been dusty for decades, the inspector can mark a sample area and suggest checking it again after the next flight season instead of treating on a guess.

Where does the inspector look in an Auckland house?

The roof space and the subfloor come first, because that is where untreated framing is exposed and where most live infestations are found. After that the exterior cladding, especially lower weatherboards and window joinery, then floors, stairs and any furniture you are worried about. Areas that cannot be reached safely are listed as not inspected rather than guessed at.

  • Roof space

    Rafters, purlins and sarking, checked from boards or joists with a light. Dust on ceiling linings is read as well.

  • Subfloor

    Piles, bearers, joists and the underside of the floorboards; ventilation and ground moisture are noted.

  • Weatherboards

    Lower boards, sills and the backs of boards where paint has failed.

  • Floors and furniture

    Rimu and kauri boards, hardwood flooring and antiques brought into the house.

Part-by-part guides cover what is typical in each: borer in floorboards, piles and the subfloor and weatherboards.

Is a borer inspection different from a building inspection?

Yes. A standard pre-purchase building inspection in New Zealand follows NZS 4306 and is a visual survey of the whole building, with borer as one item among many. A borer inspection spends its time on the timber alone and answers which beetle, whether it is live, and which members are affected. It does not replace a building report.

There is no New Zealand standard for timber-pest inspections comparable to the Australian one, AS 4349.3, as far as published sources show. That is why a building report may say only "evidence of borer" and recommend a specialist. If you are buying, the pre-purchase borer inspection page covers timing around your conditions and how the two reports fit together.

What happens after the inspection?

The findings arrive in writing, area by area, with one of three outcomes for each: no action, treatment, or a builder to assess the timber. Treatment is quoted for the members the findings identify and nothing else, and the work is timed ahead of the flight season of the beetle involved: early summer for the common house borer, autumn for the longhorn.

  1. Book

    Send the suburb, the reason and any deadline. The inspector phones back to confirm roof and subfloor access.

  2. Inspection

    Usually one visit. Roof space, subfloor, cladding and the items you raise.

  3. Written findings

    Species, activity, timbers, moisture and any structural flag, area by area.

  4. Decide

    Treat, monitor, or ask a builder. Nothing is treated that the findings do not support.

Prices for each outcome are on the borer cost page, and what treatment involves is set out under treating live borer. Where timber needs replacing, borer damage repair explains when the work needs a building consent.

Questions people ask

How long does a borer inspection take?

Most of the time goes on the roof space and the subfloor, so a compact single-storey house with easy access is quicker than a large villa with a low, tight subfloor or a house full of old furniture. Ask for an estimate when you book, and remember that the written findings follow the visit if you are working to an unconditional date.

Does someone have to be at the house during the inspection?

Someone needs to give access to the roof hatch, the subfloor and any locked areas, and it helps to be there to point out the holes or dust that prompted the call. If you are buying, the agent or vendor usually arranges access, so book early enough for that to be organised.

Can borer be found in a modern house?

Less often. Boron-treated framing resists borer, and treated framing became a requirement again for consents issued from April 2004. Houses consented in the late 1990s and early 2000s may contain untreated kiln-dried framing, and older furniture or recycled timber can bring borer into a newer house.

What if the inspector finds termites instead of borer?

New Zealand has a few native termites, but exotic termites are a biosecurity matter. The Ministry for Primary Industries asks for suspected exotic termites to be reported on its pest and disease hotline, 0800 80 99 66, and has recorded Australian subterranean termites in Auckland houses. Nothing should be treated before that call.

Before you book

Sources

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