Given the popularity of decks and DIYing them here on Workshop I thought it's important to show the perils of not installing them correctly.
In all my responses to people (and obviously the decks I build) I advise to use;
Below are the results of not following this advice. Someone installed this deck with no clearance - H3 sitting on the sand below. This deck was installed about 6-7 years ago and is beyond repair.
Decking boards are sinking. I can pull them up with just my fingers. Pressing on the rotting frame causes it to crumble away. It's become very dangerous.
Many thanks for sharing this example with the community. Did they use H3 in this situation because there wasn't enough clearance to fit the suitable H4 sizes? I've noted that in many of the low-level deck builds there just isn't enough space to fit H4 joists/bearers without adjusting the ground height first. After contacting some manufacturers it appears 90 x 45mm H4 just isn't something readily available.
What will be your solution to this issue, to dig down, raise the deck or was there actually room to fit the adequate H4 timbers already?
It's a case of making the room to be honest @MitchellMc. It adds labour and cost to do so, but you need to dig that sand away to create the 250mm clearance for H3, or at least make enough room for H4. You could rip lengths of 200x50 H4 sleepers to size. These are readily available.
If you're not going to create the right space and use the right timber, don't install a deck. The deck cost my customers about $11,000 and it's going to cost more than that to remove existing, dispose of it, create the clearance and install a new deck.
Do termites still attack H3/4/5 wood?
(I never knew there was a H5).
@Noyade H3/4/5 are all treated for termites.
H4/5 gives you the treatment against continual contact with ground/moisture and H5 can actually be submersed in fresh water.
For the benefit of others that might come across this discussion, I thought I would include the 6 general grades of treated pine.
These treatments are only effective on un-cut lengths of timber and the internal timber is not treated to the same degree. Any cut lengths must be resealed on their ends with a product similar to TWA Woodcare 300g Ecoseal Tanalised Timber Treatment to retain their H rating and characteristics.
Dunno why, but I always thought the "H" rating represented weather resistance only.