What is treated pine, and does the treatment really protect your house?
Treated pine is ordinary pine with a preservative pushed deep into the wood. It is a good product, but it is not a shield for your house.
Treated pine is softwood with a preservative inside it
Treated pine is pine timber, usually from plantation trees, infused with a preservative under pressure in a sealed cylinder. The pressure forces the liquid into the outer wood. It stays there and makes the timber a poor meal for borers, termites and decay fungi.
Untreated pine is the opposite. Its sapwood is soft, sugary and easy to eat. That is why you only build with pine once it has been treated.
The hazard class tells you where it can go
In Australia treated timber is sold by hazard class, from H1 to H6. The class is set by Australian Standard AS 1604 and describes the conditions the board will face, not how good it is.
| Class | Where it is used |
|---|---|
| H2 | Inside, above ground and kept dry, such as wall framing |
| H3 | Outside, above ground, such as decking and pergolas |
| H4 | Outside, in contact with the ground, such as fence posts |
| H5 | Heavy ground contact or severe damp, such as retaining walls |
A higher number means a heavier treatment for a harsher job. It does not mean a board is safer from termites in a general sense. The page on H3 vs H4 timber goes through the step between classes.
How to tell what you have bought
Look for the end tag or the ink stamp on the board. It should show the hazard class and the treatment type. Many boards also carry a colour mark on the end that shows the class, but the colour code differs between suppliers, so do not rely on it alone.
If a board has no stamp, you cannot tell its class by looking at it. Ask the supplier, or treat it as untreated for any decision that matters.
What the treatment does not do
This is where most people get caught. Treatment protects the piece of timber that was treated, and only where the preservative reached. It has three limits you should know about.
- Cut ends are exposed. A saw cut or a drilled hole opens untreated heartwood. Those faces need a fresh coat of an approved end-cut preservative.
- Termites can go around it. A colony can build a mud tube over treated timber, or reach the house by another route, and feed on untreated wood nearby.
- Treatment is not a barrier system. Protection for the house comes from a termite management system installed to AS 3660 and kept up with regular inspection.
So treated pine is a sensible supporting layer, not the main defence. Do termites eat treated pine? looks at what happens when they meet it.
Is treated pine worth using?
Yes, where the framing or outdoor timber needs to last. Use the class the standard asks for and not a notch above, because paying for a higher class inside a dry frame buys you nothing. Using too low a class in the ground is the real mistake, since the board will rot early and give termites an easy way in.
Treated timber also still needs looking at. If you find mud tubes, hollow-sounding boards or frass in or near treated pine, do not spray or break it open. Leave it alone and book a licensed timber pest inspection. Disturbing the colony can push it out of sight, and the damage carries on where nobody is looking.
This site does not certify any product or brand. For the preservative itself, see timber preservatives.
Frequently asked questions
What is treated pine?
It is pine timber that has been infused with a preservative under pressure. The treatment makes the wood much less attractive to borers, termites and decay fungi, and the hazard class on the stamp shows where it can be used.
Is treated pine termite proof?
No. Treatment protects the treated wood where the preservative reached, but termites can build mud tubes over it, enter through cut ends or reach the house by another route. Termite protection comes from a management system and inspections.
How can I tell which hazard class a board is?
Check the end tag or ink stamp for the class and treatment type. Colour marks vary between suppliers, so ask the supplier if the board has no clear stamp.
Do I need to seal cut ends on treated pine?
Yes. A cut or drilled hole exposes untreated wood, so apply a suitable end-cut preservative to those faces and follow the product label.
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