H2 timber: what the rating covers and what it leaves out
H2 timber is treated for dry use inside the building. It is a narrower promise than most people assume.
What H2 timber is
H2 is a hazard class for treated timber in Australia, set under AS 1604. It marks timber for use inside buildings, above the ground and kept dry. Think roof trusses, wall frames and floor joists in a house that stays weathertight.
The treatment is aimed at insects, mainly borers and termites, not at rot. Rot needs sustained wet timber, and H2 timber is not meant to live in those conditions. The label on the pack or the tag on the end of the board tells you the class and treatment.
Where H2 fits and where it does not
| Use | H2 suitable? |
|---|---|
| Interior wall frames and roof trusses | Yes, kept dry and above ground |
| Floor joists inside the building envelope | Yes, if the subfloor stays dry |
| Decking, pergolas, exterior cladding | No. This is H3 territory |
| Posts in or touching soil | No. This is H4 or higher |
For the next class up, see H3 timber, and for the comparison, H3 vs H4 timber.
Does H2 timber stop termites?
It helps, but it is not a termite barrier. The treatment makes that piece of timber a poorer meal. It does nothing for untreated timber nearby, and a colony can still build a mud tube over treated framing to reach something else.
A house relies on a termite management system under AS 3660 and regular inspection. Treated framing is a supporting layer. Termite treated timber covers what the label promises.
Cut ends and damp subfloors
Treatment does not always reach the heartwood, and a saw cut exposes it. Brush cut ends and drilled holes with a preservative made for the job, following the instructions on the tin.
Damp is the other weak point. H2 timber that stays wet, from a leaking pipe or a poorly ventilated subfloor, is outside its rating. Fix the moisture source rather than relying on the class.
What to do if you find damage in H2 framing
If you see mud, frass or timber that sounds hollow, do not spray or break it open. Leave it as it is and book a licensed timber pest inspection. Any treatment is for a licensed pest management technician using APVMA registered products. This site does not certify any product or brand.
Frequently asked questions
What is H2 timber used for?
H2 is treated for use inside buildings, above the ground and kept dry, such as wall frames, roof trusses and floor joists.
Can I use H2 timber outdoors?
No. Outdoor timber exposed to rain needs a higher class, normally H3 above ground. Check the requirement in AS 1604 or ask your builder.
Is H2 timber termite proof?
No. The treatment slows damage in that piece of timber, but it does not protect the rest of the house. A termite management system and regular inspections do that job.
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.
- Department of Health, Victoria. Pest control - termites
- Queensland Building and Construction Commission. Protect against termites - termite management systems and inspections
- Standards Australia. Australian Standards (AS 3660 termite management, AS 4349.3 timber pest inspection)