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Damage repair

Repairing borer damage: builder, consent or neither

Treatment stops borer feeding; it does not put back the timber the larvae have eaten. Where a borer inspection finds members that are soft, crumbling or hollow, the next step is a builder, and the question becomes whether the repair is ordinary maintenance or building work that needs a consent.

Borer damage needs a builder when timber has lost strength: boards or joists that crumble or dent under a probe, springy floors, longhorn tunnels in bearers, or piles that no longer carry their load. Replacing some damaged members with comparable ones in the same position is generally exempt from building consent. Complete or substantial replacement of structure, including a full re-pile, needs a consent.

With your agreement the findings go to a builder who quotes the repair. The repair is priced separately from any borer treatment, and no builder is named on this site.

When is borer damage structural?

Damage is structural when a member that carries load has lost enough timber to weaken it. The signs are timber that crumbles or lets a probe sink in, floors that bounce or slope, cracks running along lines of holes, and bearers or joists with longhorn tunnels. Scattered round holes in the sapwood edge of a firm joist usually are not structural, because the common house borer normally feeds only in sapwood.

  • Floors. Soft or crumbling boards, springy areas, boards cracking along a line of holes.
  • Subfloor. Bearers or joists hollow when probed, piles soft right through, oval longhorn holes in heavy timbers.
  • Cladding. Weatherboards that give under a thumb, hollow lower boards and sills.
  • Roof space. Rafters or purlins with heavy damage, especially below old leaks.

The two-toothed longhorn is the beetle most often behind structural findings, because its larvae tunnel through heartwood for 2 to 11 years and can leave a thin outer shell. Consumer NZ notes its damage is usually severe and the timber often has to be replaced.

How many piles can be replaced without a building consent?

The Building Act sets no number. A Marlborough District Council newsletter, relaying a BRANZ summary of MBIE determinations, suggests replacing up to about 20% of a house's piles is generally not treated as substantial, with ground conditions, the building's size and use, and the piles' structural role weighed as well. Replacing piles in stages to stay under that figure does not get around the rule.

Treat the 20% figure as a rule of thumb drawn from MBIE determinations relayed by BRANZ, not as a threshold, and check with Auckland Council for your house. A full re-pile is substantial structural replacement and always needs a consent. The subfloor findings themselves are explained under borer in piles, bearers and joists.

Who can carry out consented structural repairs?

Consented work on a house's primary structure, which MBIE lists as including foundations, subfloor framing, floors and walls, is restricted building work. It must be carried out or supervised by a Licensed Building Practitioner (LBP) in the right licence class, such as Foundations, or by an owner-builder with an exemption. Repairs that are exempt from consent are not restricted building work and do not need an LBP.

MBIE notes that breaches can bring fines of up to $50,000. Before consented work starts, ask the builder which LBP licence class they hold for it and who will sign off the work.

What does re-piling cost in Auckland?

Published price guides vary widely, because re-piling depends on the number of piles, access, the ground and whether floors need relevelling. Builders' published guides put a partial re-pile from about $5,000 to $35,000, and a full re-pile of a bungalow or villa from about $50,000 to $150,000 or more, before consent and engineering fees. GST treatment varies between guides, so treat these as rough published figures, not quotes.

Published re-piling figures, New Zealand builders' guides (a guide only)
Item Published range
Partial re-pile (roughly 10–20 piles) About $5,000–$35,000
Small bungalow, full re-pile About $50,000–$95,000 + GST
Larger villa, full re-pile About $80,000–$150,000 or more + GST
Building consent fees About $2,000–$5,000
Engineer About $1,000–$3,000

A borer finding does not by itself mean a full re-pile. In many houses only some piles or bearers are affected, and the inspection findings say which, so the builder can quote for the damaged members rather than the whole foundation.

Should borer be treated before or after the repair?

Before, or at the same time. The timber that stays in place still holds larvae if the borer is live, so it needs treating whatever is replaced, and replacement timber should itself be treated. Leaving a leak or a wet subfloor in place undoes both jobs. The usual order is inspection, moisture fixes, treatment of the timber that stays, then the builder's repair, with a check after the next flight season.

  1. Inspection

    Species, activity, extent and a structural flag where timber has lost strength.

  2. Moisture

    Leaks, vents and ground moisture fixed first.

  3. Treatment

    Timber that stays in place treated ahead of the beetle's emergence.

  4. Builder

    Damaged members replaced, with consent where the work is substantial.

  5. Recheck

    Treated areas looked at again after the next flight season.

The repair and the borer treatment are separate quotes. Treatment prices are on the borer cost page.

Questions people ask

Is borer damage bad?

Old, inactive holes in firm timber are mostly cosmetic. Damage matters when timber that carries load has lost strength: joists or bearers that crumble, floors that bounce, longhorn tunnels in heavy members. That needs a builder, and sometimes a consent. Most houses with borer fall somewhere between the two, which is why the findings record each area separately.

Can I replace borer-damaged floorboards myself?

Replacing some damaged boards with comparable boards in the same position is generally exempt from building consent and is not restricted building work, so an owner can do it. The work still has to comply with the Building Code. Check the joists below before relaying boards, and treat any live borer in the timber that stays, or the new boards sit on an active infestation.

Does a full re-pile need a building consent?

Yes. A full re-pile is complete replacement of the foundations, which contribute to the building's structural behaviour, so it falls outside the Schedule 1 exemption and needs a building consent. Consented foundation work on a house is restricted building work, carried out or supervised by a Licensed Building Practitioner with the right licence class. Replacing a few piles like for like is a different case.

How do I know if borer is still active before a repair?

Fresh signs are pale, clean-edged holes and fine dust that comes back after cleaning, especially over summer, when the common house borer emerges. Dark holes with no new dust are usually historic. If the repair is going ahead regardless, the timber that stays should be judged and, if live, treated, so the inspection comes first.

Before the builder

Sources

Have the damage assessed