Do termites eat treated pine and hardwood?
Yes to both, with qualifications that turn out to be the whole answer. No timber in an Australian house is termite-proof.
Two words that get used interchangeably and should not be
Treated means a preservative has been forced into the timber. Durable means the species' own heartwood naturally resists attack. They are different mechanisms and are rated on different scales. Neither means immune.
Treated pine and the H scale
Australian preservative treatment is described by hazard class, written as H1 through H6. The number does not describe how much protection you get. It describes the exposure the timber is rated for. That distinction is where most of the real-world failures come from.
| Class | Intended situation |
|---|---|
| H1 | Inside, above ground, protected from weather. Insect attack other than termites |
| H2 | Inside, above ground, protected: includes protection against termites. This is the framing class |
| H3 | Outside, above ground, exposed to weather |
| H4 and above | In contact with the ground, and beyond |
So H2 framing is treated against termites, in the situation it is rated for: dry, above ground and inside a building envelope. Use the same board in the ground and the rating no longer describes what you are asking of it.
The failure that keeps happening: cut ends
Preservative penetration is not uniform to the centre of every piece. When a treated board is cut, drilled or notched on site, untreated or less-treated material is exposed. Manufacturers specify that cut ends be re-sealed with a suitable preservative for exactly this reason. And on a busy site it is one of the easiest steps to skip. A treated frame with unsealed cuts has an entry point at every one of them.
Hardwood and natural durability
Some Australian hardwoods have genuinely durable heartwood, which is why they were traditionally used for stumps, sleepers and posts. But three qualifications matter more than the durability rating itself:
- Sapwood is not durable. The outer band of any tree, including a highly durable species, has little natural resistance. A board is not all heartwood, and the sapwood is the part termites reach first.
- Durability is rated against exposure, in ground and above ground, and against decay as well as insects. A species durable above ground may not be in soil contact.
- Resistance is not a wall. Termites will build over and around timber they do not prefer to reach timber they do. A durable bearer does not protect the pine framing above it.
The other materials
QBCC lists termite-resistant construction materials alongside management systems. As well as treated timber, that means masonry, steel and concrete. Termites do not eat any of them, but they will build mud tubes over all of them to reach timber. That is why a steel-framed house still gets a barrier and still gets inspected. There is timber in every house: joinery, flooring, cabinetry, door frames, roof battens.
What this means in practice
Timber choice is one layer of defence, and it is the layer you are least likely to change on an existing house. It works alongside the others rather than instead of them. The others are correctly treated framing, a barrier installed at the penetrations and perimeter, no timber in ground contact and no damp against the walls, and an annual inspection.
A house with all four is in a strong position. A house relying on the treated pine alone is relying on a rating for a situation that may not be the situation it is in.
Frequently asked questions
Is H2 treated pine termite-proof?
No. It is treated to resist termite attack in the situation it is rated for. Dry, above ground, inside the building envelope. Unsealed cut ends, ground contact or persistent damp all take it outside that situation.
Do termites eat hardwood?
Yes. Durable heartwood in some species resists them well, but the sapwood in the same board does not, and durability varies enormously between species and between in-ground and above-ground use.
Is a steel-framed house safe from termites?
The frame is, but the house is not. Termites build tubes over steel and concrete to reach the timber that is still there (flooring, joinery, battens, cabinetry) so barriers and inspections still apply.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- Standards Australia. Australian Standards (AS 3660 termite management, AS 4349.3 timber pest inspection)
- Queensland Building and Construction Commission. Protect against termites — termite management systems and inspections