Depending on the type of hardwood, H3 treatment might not be needed. A marine environment is not particularly hazardous for dense hardwoods, but care is needed in specifying fasteners since a salty atmosphere is highly corrosive to metals. Durability Class 1 hardwoods such as ironbark, spotted gum, blackbutt etc. would achieve a probable life of up to 40 years out of ground contact according to Australian Standard 5604:2022, Timber - Natural durability ratings. In fact the heartwood of such species is difficult to treat effectively.

The design of timber rounds is covered in AS 1720.1-2010, Timber structures, Part 1: Design methods. Table 6.1 in Section 6 gives the relationship between the Strength Group of a species and its Stress Grade. For example, radiata pine falls into Strength Group S6 (unseasoned) and the related stress grade is F11. If not from a 'mature' tree the designer would apply a reduction factor. It is assumed that the round material complies with AS 3818.11, which deals primarily with allowable splits and straightness.

The life span of H3 treated pine compared to various hardwoods can be estimated by reference to our Technical Design Guide no. 5 titled Timber Service Life Design.

We can now advise that Regulatory Information Report 41117.11 has been extended to 30 April 2025 by Warringtonfire Australia - refer Letter of Extension LOE 1.2 available on our website here: https://www.woodsolutions.com.au/resources/standards-codes/fire-test-reports.