What the H levels actually rate, why cut ends matter, and the difference between the heartwood durability of a species and the sapwood in the same board.
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Timber: what termites eat and what resists
No timber is termite-proof. Some are resistant, some are treated, and the difference between those two words matters.
Resistant is not immune, and treated depends on the level
Two questions come up more than any others: do termites eat treated pine, and do they eat hardwood. The short answers are yes and yes. But with enough qualification that the long answer is genuinely useful.
Treatment levels in Australia run on the H scale, and the level describes the exposure the timber is rated for, not a promise of immunity. H2 is for internal framing above ground in a protected situation; the treatment is there to resist insect attack, including termites, in that specific application. Timber in ground contact needs a much higher level. The common failure is not the treatment failing. It is timber used outside the exposure it was rated for, or cut ends and drilled holes left unsealed so the untreated core is exposed.
Natural durability is a separate scale. Some Australian hardwoods have heartwood with real resistance to termites, which is why they were traditionally used for stumps and sleepers. But the sapwood of even a durable species is not resistant, and a piece of timber is not all heartwood. Resistance also does not mean termites will not build across it to reach something they prefer.
The practical consequence is that timber choice is a layer of defence, not the defence. A house framed in H2 treated pine with a correctly installed barrier and an annual inspection is in a good position. The same timber with a garden bed over the slab edge and no inspection for a decade is not.
Timber guides
What a natural durability rating actually covers, why sapwood is the catch in every durable board, and where resistant timber is worth specifying.
Why “termite treated” is not a class, what the brand stamped on the timber tells you, and why envelope treatment turns every site cut into an opening.
Termites eat anything built from plant fibre. The useful question is not what they like but what in your house they can reach.
The H number tells you where a piece of timber may be used. It does not tell you the house is safe from termites.
H3 timber is treated for outdoor use above the ground. Where it fits, what it does about termites, and the cut-end mistakes to avoid.
H2 timber is treated for dry use inside the building. Where it fits, what it does about termites, and the damp and cut-end mistakes to avoid.
H4 timber is treated for ground contact. Where it fits, what it does about termites, and the mistakes that undo the rating.
H5 treated pine is for heavy ground contact. Where it fits, how it differs from H4, and why it is not a termite barrier.
Copper based, CCA, LOSP and boron explained, and how the preservative links to the hazard class and to termites.
Treated pine explained: the preservative, the hazard class stamp, what the treatment protects and why it is not termite proofing.
No wood is termite proof. Treatment, barriers and building details compared, and why inspection still matters.
Treated pine framing explained: the H2 class, what the treatment covers and why a framed house still needs inspecting.
Treated pine can rot. Why it happens, how rot invites termites and what to do about soft timber.
H6 is the marine class under AS 1604. Where it belongs, and why it is not a termite answer for a house.
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