H codes: Hazard treatments H1 - H5

H codes (H1 to H5) are conditional use codes representing appropriate levels of preservative treatments (against biological decay) that are required for using a specific timber in a specific application and location. Each code (H1, H2, H3, H4, H5) represents a different, required minimum preservative treatment.

H level      H levels represent the level or degree of biological hazard that timber will be exposed to in a specified application. The appropriate level of treatment (H1, H2, H3, H4 or H5) describes the extent of preservative treatment (retention and penetration) required (when combined with the timber’s natural durability) to protect the wood against the identified biological hazard/s.

H1             The minimum level of preservative treatment required to protect the timber from attack by insects other than termites. H1 preservative treatments are suitable in above-ground, well-ventilated situations protected from weather and wetting.

H2             The minimum level of preservative treatment required to protect the timber from attack by insects, including termites. H2 preservative treatments are suitable in above-ground, well-ventilated situations protected from weather and wetting.

Note 1: For timber treated to H2. For timber treated to H2, for use south of the Tropic of Capricorn only, the designated treatment brand is H2 (F).The designated brand of timber that may be used throughout Queensland is H2.

Important: H3*, H4* and H5* codes

*Timbers allocated conditional use codes H3, H4 or H5 can only be used in the specified application if that timber can be commercially treated to a minimum H3, H4 or H5 level (as required). N.B. Currently, the heartwood of most hardwood timbers and some softwood timbers cannot be treated to this level of protection. The timber treater is to ensure that their process has achieved the required level of penetration to meet the stated H level specification.

*H3          The minimum level of preservative treatment required to protect the timber from attack by decay fungi and insects, including termites. H3 preservative treatment offers protection in situations above-ground, exposed to the weather or periodic wetting. Depending on the application, preservative treatment to provide protection in H3 conditions can involve one of two levels. The lower retention level must not be used in a load-bearing application where routine inspection and maintenance cannot be readily carried out. The lower retention level applies only to vertical (water-shedding) applications that can be maintained regularly. In Australian Standard AS 1604.1-2005 these constraints are signified in the brand by the letter ‘A’; that is, H3A.

N.B. Currently, the heartwood of most hardwood timbers and some softwood timbers cannot be treated to this level of protection. The timber treater is to ensure that their process has achieved the required level of penetration to meet the stated H level specification.

*H4           The minimum level of preservative treatment required to protect the timber from attack by insects, including termites, and severe decay. H4 treatments are suitable for use in situations where the timber is in contact with the ground or is continually damp. H4 is appropriate for less critical ‘non-structural’ applications and/or where the decay hazard zone indicates a lower in-ground hazard.

N.B. Currently, the heartwood of most hardwood timbers and some softwood timbers cannot be treated to this level of protection. The timber treater is to ensure that their process has achieved the required level of penetration to meet the stated H level specification.

*H5           The minimum level of preservative treatment required to protect the timber from attack by insects, including termites, and very severe decay. H5 treatments are used in situations where timber is in contact with the ground or fresh water.

N.B. Currently, the heartwood of most hardwood timbers and some softwood timbers cannot be treated to this level of protection. The timber treater is to ensure that their process has achieved the required level of penetration to meet the stated H level specification.