H5 treated pine: what the rating covers and what it leaves out
H5 is treated for heavy ground contact. That makes the pier tougher, not the house next to it termite proof.
What H5 treated pine is
H5 is the heaviest everyday hazard class in AS 1604 for timber that stays in the ground. It sits above H4 and is meant for structural timber in ground contact, in wet or poorly drained soil, or in fresh water. Think house piers, poles and heavy retaining walls.
The class describes how much preservative has to soak into the wood and how deep. It is not a species. Most H5 pine in Australia is radiata pine pushed full of preservative under pressure.
H5 against H4 and H3 at a glance
| Class | Typical use |
|---|---|
| H3 | Outdoors above the ground, such as decking and pergolas |
| H4 | In ground contact, such as fence posts and garden sleepers |
| H5 | Heavy ground contact and structural use, such as piers and poles |
The pairing is covered in H3 vs H4 timber. If you are choosing between H4 and H5 for a post that carries load, the design or your engineer decides it, not the price of the pack.
Does H5 treated pine stop termites?
It makes that piece of timber a poor meal. It does not make the house safe. Termites can still build mud tubes over a treated pier to reach untreated framing above it.
That is why a treated pier is not the same as a termite barrier. The management system under AS 3660 and a regular inspection are what protect the building. Read termite treated timber for what the label does and does not promise.
Cut ends and drill holes are the weak point
Treatment is deepest at the surface and thinner at the core. A saw cut or a drilled bolt hole opens untreated wood. Brush every cut end and hole with a preservative made for the job, following the directions on the tin. Do it before the post goes in the ground, not after.
Mistakes that undo the rating
- Cutting H5 to length on site and leaving the cut bare. The fresh cut is the first thing to rot.
- Burying the wrong end. Use the end the supplier marks for the ground, if it is marked.
- Letting H5 touch the house. A treated pier or garden bed hard against the wall hides the join and gives termites a path.
- Treating the class as a guarantee. H5 says where the timber may go, not that the structure is protected.
What to do if you find damage in the timber
If you see mud tubes, frass or a post that sounds hollow, do not spray it 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.
When to use H5, and when H4 or H3 is enough
Use H5 when timber is structural and sits in heavy ground contact, wet or poorly drained soil, or fresh water. For ordinary in-ground jobs H4 is usually the class the job calls for, and above the ground H3 does the work.
| Situation | Usual class | Why |
|---|---|---|
| House piers and poles | H5 | Structural timber in heavy ground contact |
| Heavy retaining walls, or posts in wet, poorly drained soil | H5 | The harshest everyday in-ground conditions |
| Timber standing in fresh water | H5 | One of the uses the class is meant for |
| Fence posts and garden sleepers | H4 | Ground contact without the structural load |
| Decking and pergolas above the ground | H3 | Outdoors but kept out of the soil |
| A post that carries load and you are unsure | Ask | The design or your engineer decides, not the price of the pack |
Whatever the class, it describes how the timber resists decay and attack in that one piece. It does not protect the house. Termites can still tube over an H5 pier to reach untreated framing above, so the building still needs a termite management system and regular inspections. H3 vs H4 timber covers the lighter classes in more detail.
Frequently asked questions
What is H5 treated pine used for?
H5 is for structural timber in heavy ground contact or wet ground, such as house piers, poles and larger retaining walls.
Is H5 better than H4?
It carries a heavier treatment, so it suits harsher in-ground uses. For a fence post, H4 is usually the class the job calls for.
Is H5 treated pine termite proof?
No. It resists attack in that piece of timber, but termites can still tube over it to reach untreated framing. A termite management system and regular inspections protect the 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.
- 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)