When wood is treated to an H1 level, it is required to be protected from attack from a range of insects except for termites. H1 treated lumber is recommended for use above-ground in well-ventilated areas not exposed to weather and wetting. Examples include timber designated for interior use such as furniture, framing and the like.

Wood that has been treated to a minimum H2 level is protected from insect attack including termites. H2 timber is still intended to be used in above-ground, well-ventilated areas that are not exposed to weather and wetting and is ideal for residential and light commercial projects including interior framing and trusses.

Timber treated to a minimum H3 treatment level is protected against insects, termites, and moderate decay and is suitable for outdoor applications exposed to periodic wetting (where the timber can dry out). H3 timber durability offers long-term protection in applications such as windows and doors, handrails, pergolas, picnic tables, and more.

Timber that has been treated to a minimum H4 level is protected against insects, termites, and severe decay. It is suitable to be used in applications where it is in contact with the ground and is exposed to continuous moisture. Typical applications of H4 treated timber include pergola posts and landscaping timbers.

H5 treatment is offers the highest levels of protection against insects, termites, and very severe decay. It is ideal for situations where the timber is in contact with the ground or fresh water. H5 treated timber is ideal for retaining walls, piling, house stumps, and other landscaping applications.