H3 treated timber
H3 treated timber: preservative-treated timber for above-ground exterior use (decking, cladding, fence rails). H4 required for ground contact. Australian standard.
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H3 is an Australian hazard level designation for preservative-treated timber used in above-ground exterior applications where the timber is exposed to weather but is not in contact with the ground. Typical H3 applications include deck boards, bearers, joists, fence rails and palings, and external cladding.
The H code (H1 to H5) indicates the minimum level of chemical preservative treatment required to protect the timber against fungal decay and insect attack for the intended exposure. H3 timber must not be used in ground contact; H4 is the minimum for posts or framing in contact with soil or maintained damp conditions. H5 is required for in-ground timber in fresh water or very severe decay conditions.
Always check the product’s treatment certification to confirm the hazard level stamped or tagged on the timber before purchase. Do not rely on visual inspection to distinguish H2 from H3 or H4.
Also known as: H3 pine, H3 treated pine, hazard level 3
Category: Timber specification, treatment
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Last updated: 2026-05-08. Verified: 2026-05-08.