Borer library

Is borer a deal breaker when you are buying a house?

Usually not, but sometimes it should be, and a building report rarely tells you which. Most New Zealand houses built from untreated timber have some old borer holes. What decides it is whether the beetle is still active, which timbers it is in and how weak they are, which is what a pre-purchase borer inspection finds out before you go unconditional.

Updated 6 October 2026

Borer is rarely a deal breaker on its own. Old, inactive holes in roof framing or the sapwood edges of floorboards are common in villas and bungalows and often need nothing. It becomes serious when it is live in structural timber, when the native longhorn is in piles or bearers, or when a damp subfloor is keeping an infestation going. Those findings should change the price, the conditions or the decision.

When should borer change your offer on a house?

Borer should change your offer when the findings point to real cost: live borer in structural members such as piles, bearers, joists or wall framing; oval longhorn holes in heartwood; timber that dents or crumbles when probed; or a damp, badly ventilated subfloor that will keep the beetle going. Each of these means treatment, builder repairs or both, and the cost belongs in your thinking before you commit.

Live borer in structure. Fresh dust and clean holes in framing mean larvae are still feeding, and they spend about 3 to 4 years in the wood before they emerge.
Two-toothed longhorn in bearers or piles. Ambeodontus tristis tunnels through heartwood as well as sapwood, and badly attacked timber can be left as a thin shell. Consumer NZ describes its damage as usually severe.
Soft or crumbling timber. This is a builder's matter, and replacing a lot of structural timber may need a building consent.
A damp subfloor. Moisture keeps borer active and invites decay. Fixing it is part of the cost.

When can you live with borer in a house you are buying?

Borer usually need not stop a purchase when it is historic, when it is confined to sapwood edges, or when the framing is boron-treated. The common house borer normally attacks only the sapwood of rimu, kahikatea and pine, so a row of holes along the edge of a joist often leaves the heartwood doing the work. Dark, weathered holes with no fresh dust usually belong to beetles that left long ago.

Treated framing is treated to resist borer, so in a house built after boron treatment came into general use the structure is less of a concern than floors, joinery or recycled timber. A finding of old, inactive borer in an older house is closer to a description of its age than to a defect.

What should you ask the agent and the vendor about borer?

Ask directly whether the vendor knows of borer, past treatment or replaced timber, and ask for any reports or invoices. Under the professional conduct rules for real estate agents, an agent does not have to look for hidden defects but must tell you about defects they know of, and borer damage known to the agent falls within that. This is general information about the rules, not legal advice.

Has the house been treated for borer, when, and by whom? Is there an invoice or a report?
Have any piles, bearers, joists, floorboards or weatherboards been replaced, and was a consent needed?
Is there a recent building report, and can you see the full report rather than a summary?
Can you or your inspector get into the roof space and the subfloor before your condition date?

Rule 10.7 goes further: where a reasonably competent agent would suspect a hidden defect, they must either get the vendor's confirmation, backed by evidence or expert advice, that there is no defect, or make sure you are told of the risk so you can get advice. Under rule 10.8 an agent must stop acting for a vendor who tells them to hold such information back. The legislation website flags 2026 amendments not yet built into its copy of the rules, so check the current version with your lawyer.

How can borer findings be used in a negotiation?

Buyers commonly use borer findings in one of three ways: asking for a lower price that reflects treatment and repair costs, adding or extending a condition while a builder looks at weakened timber, or asking the vendor to have the treatment done before settlement. Which of these suits your contract and situation is a question for your lawyer, and this page is general information, not legal advice.

Whatever you ask for, written findings make it easier. A finding that names the beetle, the members affected and whether any of them need a builder gives both sides something concrete to price, where a single line saying "evidence of borer" does not. If the vendor arranges treatment, ask for the written findings and the invoice so you know what was treated and when.

What does a borer finding cost to deal with?

Published Auckland prices put treatment of a roof space at about $350–$600 + GST and a subfloor at about $450–$750 + GST. Floors, weatherboards and furniture are quoted after an inspection. Builder repairs are separate and are where the larger numbers sit: replacing a few members like for like is a modest job, while substantial replacement of structural timber needs a consent and costs far more.

The borer cost guide sets out the published ranges and what moves them, and borer damage repair explains when weakened timber becomes a consent matter.

Do villas and bungalows nearly always have borer?

Most have some. Villas and California bungalows in Auckland were mostly built before boron treatment of framing was introduced in 1952, from untreated native timber such as rimu and kahikatea, and many have had a century for the common house borer to find the sapwood. For these houses the useful question is not whether there is borer, but whether it is live and where.

Buyers of houses built or extended between about 1995 and 2005 should ask a similar question for a different reason: untreated kiln-dried framing was allowed for part of that period. The guide to house borer by build year covers each era.

Questions people ask

Is borer the biggest red flag in a house inspection?

Usually not. Weathertightness problems, structural movement and decay can be bigger issues. Borer becomes a major flag when it is live in structural timber, when the native longhorn is in piles or bearers, or when probing finds soft members. Old borer holes on their own turn up in a great many older New Zealand houses.

How serious is borer in a house?

It depends on the beetle and the timber. The common house borer feeds mainly in sapwood and works slowly, so damage builds over years and is often limited to edges. The two-toothed longhorn attacks heartwood too and can hollow a member out. Live borer in structural timber is serious; old holes in floorboard edges usually are not.

Should I buy a house with borer?

Many people do, and many older houses have some. The decision rests on what the findings say: whether the borer is live, which timbers carry it, whether anything needs a builder, and what that will cost. With that in writing before your condition date, you can decide on facts. Talk to your lawyer about how to use the findings in your contract.

Does treated framing stop borer?

Boron-treated H1.2 framing is treated to resist borer, and the general use of treated timber has greatly reduced house borer in New Zealand. It is not borer-proof in every case: boron is water-soluble and can leach out of timber that stays rain-wet for long periods. Untreated floors, joinery and recycled timber in the same house can still carry borer.