Termite resistant timber: what the rating means
Resistant is a rating for heartwood in a stated exposure. It is not a property of the plank, and it is never a substitute for a barrier.
Is there such a thing as termite resistant timber?
Yes, with two qualifications that turn out to be most of the answer. Resistance is rated for the heartwood of a species, not for the board you are holding. It is also rated against a stated exposure (in the ground or above it) rather than as a blanket property. A timber that resists termites well as a post above ground may not resist them buried. The outer part of that same post has almost no resistance at all.
Nothing on the market is termite-proof. Australia's building rules treat resistant materials as one element of a termite management system, not as a replacement for one. That is exactly the right way to think about it on your own house.
Natural durability: what is actually being rated
Australian natural durability ratings describe the heartwood of a species (the dense, dead inner wood) and they are published separately for different situations. The key points, before any species name comes into it:
- In-ground and above-ground are rated separately. Soil contact is a far harsher exposure, and a species can rate well in one and poorly in the other.
- Termite resistance and decay resistance are different things. A timber can be durable against fungal decay and still be eaten, and vice versa. Borer susceptibility is rated separately again.
- Ratings are per species, and they are published. Check the rating for the species in front of you and for the job you are asking it to do, rather than relying on a general reputation for hardness. Hardness and durability are not the same property.
Sapwood: the catch in every durable board
This is the single most important thing on the page. Sapwood has essentially no natural durability, in any species. It is the living outer band of the tree. And it is the part of the board that sits on the outside: which is the part termites reach first. A post cut from a highly durable species still has a sleeve of vulnerable timber around it unless the sapwood was removed or separately treated. Plenty of failures blamed on the species are really a sapwood problem.
The classic Australian example
White cypress is the softwood Australia traditionally specified where termite resistance was wanted. Builders used it widely for stumps and framing long before chemical treatment was routine, and it is still sold on that basis. Several Australian hardwoods have durable heartwood and were traditionally used for stumps, sleepers and posts for the same reason.
But note what that history actually shows. Those timbers were chosen for the parts of a house in the worst position: in the soil, or closest to it. That is still where specifying a resistant species earns its keep. It does very little for the rest of the building, because termites will build straight over timber they do not prefer in order to reach timber they do. A durable bearer does not protect the pine framing sitting on it.
Resistant, treated, or neither
| Approach | How it works | Where it fits | The catch |
|---|---|---|---|
| Naturally durable heartwood | The species' own extractives make the heartwood unattractive and hard to digest | Posts, stumps, sleepers, exposed structural timber | Sapwood is not durable; ratings differ in ground and above ground |
| Preservative treated timber | A preservative is forced into the timber to a stated hazard class | Framing, decking, anything rated for the exposure it will see | Cut ends and drilled holes expose untreated material unless re-sealed. See treated pine and the H scale |
| Steel, concrete and masonry | Not cellulose, so not food | Frames, piers, slabs, subfloor structure | Termites build mud tubes over all three to reach the timber that is still in the house |
| Untreated softwood | Nothing | Only where it is protected, dry and inside the envelope | Highly palatable if damp or reachable |
Where specifying resistant timber is worth it
It is worth paying for in the places that are hardest to inspect and closest to the soil (fence and pergola posts, retaining walls, sleepers, garden edging, stumps, deck bearers). As an argument for skipping anything else, it is worth roughly nothing. Two practical notes matter more than the species choice on most jobs:
- Getting the timber out of soil contact beats upgrading the species. A post on a galvanised stirrup, clear of the ground, is in a better position than a durable post buried in it.
- Resistant timber near the house still needs to be visible. A durable sleeper stacked against the wall is still a bridge over the slab edge and still hides the strip you need to see. That is an entry point problem, not a timber problem.
What it does not replace
Australian construction requires a termite management system for the building regardless of what the frame is made of. And resistant or treated timber is counted as part of that system rather than as an alternative to it. That is not red tape: it follows directly from how termites behave.
They tube over materials they cannot eat, they find the joinery and the flooring and the roof battens even in a steel-framed house. And a species rating on a delivery docket tells an inspector nothing about what is happening under the slab.
So the order that actually protects a house is unchanged. Start with timber suited to its exposure and a barrier kept in service. Keep timber out of ground contact, with nothing damp against the walls. Then add an annual inspection by a licensed inspector. Timber choice is one of those four, and it is the one you can least often change after the fact.
Frequently asked questions
What is the most termite resistant timber in Australia?
There is no single answer, because resistance is rated per species and per exposure: in-ground ratings and above-ground ratings differ, and decay resistance is rated separately from termite resistance. White cypress is the softwood traditionally specified for the job, and several Australian hardwoods have durable heartwood. Check the published rating for the species and the actual application.
Does termite resistant timber mean I do not need a barrier?
No. Australian building rules treat resistant and treated materials as part of a termite management system rather than as a substitute for one. Termites build over materials they cannot eat to reach timber they can, and every house has timber somewhere. Joinery, flooring, battens, cabinetry.
Why does the sapwood matter so much?
Because durability ratings apply to heartwood, and sapwood is the outer band on the outside of the board. The part reached first. A post from a highly durable species still has a vulnerable sleeve around it unless that sapwood was removed or separately treated.
Is hardwood automatically termite resistant?
No. Hardness and durability are different properties, and durability varies enormously between hardwood species and between in-ground and above-ground use. Some Australian hardwoods have genuinely durable heartwood; others do not.
I have durable timber and I have found mud on it. What now?
Leave it exactly as it is and book a licensed inspection. Breaking the workings open or spraying them makes the colony abandon that route and return somewhere concealed, and it destroys the evidence the inspector needs. Resistant timber having been reached is itself information worth preserving.
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