Timber Treatment
Treated Timber Explained: H Ratings, CCA and LOSP
Most outdoor and structural pine is treated to protect it from termites, borers and rot. The trick is matching the treatment to where the timber is going: get it right and it lasts for decades, get it wrong and it fails early. Here is a plain guide to the H ratings and the common treatment types.
What the H rating means
The H rating, H1 through to H6, tells you the conditions the timber can handle. The higher the number, the tougher the exposure it is treated for. It is set by the Australian Standard AS 1604, and every compliant piece is branded with a stamp or tag showing its treatment and H level. If it is not branded, it does not meet the standard.
H2 is for inside and above the ground: wall framing and flooring kept dry, protected against termites and borers. It is usually dyed for identification, and you will see it in blue or red. Blue is rated for use south of the Tropic of Capricorn, which covers South Australia, while red is rated for anywhere in the country, including the tougher termite country up north.
H3 is for outside and above the ground, exposed to the weather but not touching the soil. Think cladding, fascia, pergola beams, above-ground posts and decking.
H4 is for in the ground: fence posts, pergola posts and landscaping timber that sits in the soil.
H5 is for in the ground in wetter or heavier-duty spots: retaining walls, house stumps and building poles.
For completeness, H1 covers dry interior timber against borers, and H6 covers timber in the sea, like marine piles.
CCA, LOSP and the other treatments
CCA (copper chrome arsenate) is the classic green treated pine, long sold under brand names like Permapine. It is tough and weatherproof, covers the widest range of H levels, and is still the go-to for posts, fencing and retaining walls. It contains arsenic, which is why its use is limited in some places (more on that below).
LOSP (light organic solvent preservative) is carried in a solvent rather than water, so the timber does not swell or change shape during treatment. That makes it the pick for anything already machined or primed: weatherboards, mouldings, fascia and window and door joinery, where the profile has to stay true. It is for above-ground use.
ACQ and copper azole (brand names like Tanalith E and MicroPro) are arsenic-free, water-based treatments, usually green to brown. They are the modern choice for decking, handrails and outdoor structures where CCA is no longer allowed.
Boron is used for interior framing. It washes out if it gets wet, so it stays indoors.
Creosote is the heavy-duty, dark, oily treatment you see on power poles, railway sleepers and rural fencing.
Colour is a rough guide, but the real answer is on the tag: every compliant piece is branded with its preservative and its H level. When in doubt, read the brand, not the colour.
Where CCA cannot be used
Because CCA contains arsenic, it was restricted in 2006 after a national review found a possible risk from frequent skin contact, especially for children. It was not banned outright, but it can no longer be used for a set of high-contact jobs: garden furniture, picnic tables, outdoor seating, children’s play equipment, domestic patios, domestic decking and handrails.
For those jobs, use an arsenic-free treatment instead. CCA is still fine, and still common, for posts, fencing, retaining walls, poles and other structural or in-ground work where skin contact is limited. It is also why you will not find CCA timber in new playgrounds or school seating.
Which treatment for your job
Internal framing: H2. External framing, cladding and joinery: H3, usually LOSP so the machined timber keeps its shape. Decking: H3, arsenic-free. Pergolas: H3 for members above the ground, H4 for posts set in the ground. Retaining walls and posts in the ground: H4 or H5. If you are not sure, tell us the job and we will match the treatment.
Handling treated timber safely
A few sensible habits go a long way. Never burn treated timber or its offcuts, because burning CCA concentrates arsenic in the smoke and ash. Cut it outside, wear a dust mask and eye protection, and wash your hands before eating or drinking. Do not use the sawdust or offcuts in garden beds, compost, mulch or animal bedding. Offcuts go in general waste, not the fire.
Where We Fit In
We carry treated pine across the range: MGP10 framing in H3 plus H4 treated posts, LOSP-primed finger-jointed pine for weatherboards, mouldings and joinery, and treated timber for decking, pergolas, fencing and landscaping. Not sure which treatment your job needs? Send us the details and we will sort it out.
For more on where structural pine comes from and how it is graded, see where Australia's structural pine comes from.
Treated Timber FAQs
The H rating (H1 to H6) tells you the conditions treated timber is protected for. The higher the number, the tougher the exposure. H2 is interior framing, H3 is outside above the ground, H4 is in the ground, and H5 is in the ground in wetter or heavier-duty spots. It is set by the Australian Standard AS 1604, and every compliant piece carries a stamp or tag showing its treatment and H level.
CCA (copper chrome arsenate) is the classic green treated pine, water-based and tough, used for posts, fencing and retaining walls. LOSP (light organic solvent preservative) is carried in a solvent instead of water, so the timber does not swell or change shape during treatment. That makes LOSP the choice for machined and primed timber like weatherboards, mouldings and window joinery, for above-ground use.
Yes. CCA was not banned outright. Since 2006 it cannot be used for a set of high-contact jobs such as decking, handrails, garden furniture, seating and playground equipment, but it is still legal and common for posts, fencing, retaining walls, poles and other structural or in-ground work.
A domestic deck sits outside and above the ground, so it needs H3. Because CCA is no longer allowed for domestic decking, use an arsenic-free treatment such as ACQ or copper azole. Tell us your deck and we will supply the right treated timber.
No. Never burn treated timber, especially CCA. Burning concentrates arsenic, copper and chromium in the smoke and ash, which is toxic. Cut it outside, wear a dust mask, wash your hands afterwards, keep the offcuts and sawdust out of garden beds and compost, and put offcuts in general waste rather than the fire.
Get the Right Treated Timber
Tell us the job and where the timber is going, and we will match the treatment and H level and get pricing back to you.