H3 Treatment
Preservative level for outdoor, above-ground timber exposed to the weather but not in soil, suitable for cladding, fascia, pergolas, and decking boards.
Hazard Class 3 under AS/NZS 1604.1 covers timber used outdoors and above-ground, exposed to weather and periodic wetting but not buried or in regular contact with soil. Typical uses include decking boards, pergola rafters, weatherboards, fascia, and external trim. Common H3 chemistries include LOSP, ACQ, and copper azole, each with retention loadings prescribed in AS/NZS 1604. H3 timber resists fungal decay, termites, and borers under typical Australian outdoor exposure. For buyers, H3 is not adequate for posts in ground or for components subject to constant wetting; specify H4 or H5 for those uses. Always confirm the end-tag, and seal cut ends with a compatible preservative to maintain protection.
Values and references on this page are indicative and drawn from common industry sources. Always verify the current AS/NZS standard, manufacturer data sheet or NIAA policy publication before relying on figures for design, specification or compliance work.
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