Did you know only certain types of timber can be inserted into the ground? Many types of timber will decay if inserted directly into the ground. And many types of timber specify that they must be able to be easily replaced if they are inserted directly into the ground. Quite simple and easy if this is just a fence… but for anything more complicated or structural; not so simple!
So the base of a timber posts is best raised above the surface or ground level with a metal post stirrup. This prevents water pooling around the timber at ground level or moisture from the ground seeping up which can cause premature decay of the timber post. In areas where termite activity is a problem, the use of a post support allows a visual inspection zone.
Posts in contact with the ground shall be either preservative treated pine or In-ground Durability Class 1 hardwood, with any sapwood preservative treated. Some In-ground Durability Class 2 hardwoods and cypress (refer Table 1) may be used for in-ground applications if they can be easily replaced should decay occur.[table “121” not found /]
You can download this table as a PDF below
QBCC also have an article on Residential Timber Decking which includes useful information on the correct installation of posts.