H4

In Australia, H4 is a hazard level for treated lumber that indicates the level of protection against decay and insect attack. The H4 treatment is a heavy-duty treatment and is suitable for use in ground contact and fresh water applications.

The H4 treatment process involves treating the lumber with a preservative that contains copper, azole fungicides, and a co-biocide. This treatment provides protection against decay fungi, borers, and termites.

H4 treated lumber is commonly used for a range of outdoor applications, including landscaping, retaining walls, fence posts, and structural timber in ground contact. It is important to note that H4 treated lumber is not suitable for use in marine environments, as it does not provide protection against marine borers. For those applications, a higher hazard level treatment, such as H5 or H6, would be required.