WoodSolutions is an advisory body and we don't supply or install timber products. The only company we know of that produces hardwood timber shakes is Australian Hardwood Shingles & Shakes, website available via this link https://www.shinglesandshakes.com.au/. We are not sure if they also handle installation. If not, no doubt they have contacts in the industry and can recommend experienced contractors.

To confirm the level of treatment, samples can be sent away to a testing lab where they can be assessed against the requirements of the Australian Standard. For example, IVS Labs provide this service, website here https://www.ivslabs.com.au/. There are two aspects to be tested, penetration (depth of preservative) and retention (amount of preservative in the penetration zone). Sampling is more straightforward when the full cross-section of the piece is accessible. If it's impractical to analyse the full cross-section of the piece, eg.

It is correct that Appendix F of Australian Standard 1604.1:2021 recommends H4 treatment for fence plinths and other ground contact situations. Appendix F is "informative", ie. for information and guidance only. However Table 1.5.2, in the performance part of the Standard, lists a similar requirement and H4 treatment for timber in ground contact can be taken to be an integral part of AS 1604.1. While H3 treated plinths are not a risk to public safety, nevertheless they don't comply with Australian Standard product performance requirements.

Unfortunately no timber is classed as 'non-combustible' when tested to Australian Standard 1530 Part 1: Combustibility test for materials. The test involves placing specimens in a furnace at approximately 750°C, at which temperature they must produce only a limited amount of heat and flame.

If the house at Dromana is a holiday house, closed up and unoccupied for long periods, the moisture content of the timber is about right at 12-15%. If it is continuously occupied year round, and heated and/or air conditioned, ideally the timber should be a little drier. The wall framing will be OK - pine framing is classed as 'seasoned' at 15% or less. However, the flooring may undergo some changes if subject to further drying.

We would hesitate to call any varnish coating 'permanent' when applied to exterior timber, unless protected from the weather. Varnishes form a skin which tends to become brittle with age, causing cracking and peeling. Some varnishes perform better than others, but are best applied to new wood. Weathered wood leads to poor adhesion of the coating. For your weathered jarrah deck we suggest a deck cleaning product, followed by decking oil. Such finishes are easy to apply, and easy to maintain when re-coating is necessary.