I am putting up a tanalised shed but I want to make the roof a bit
wider and longer, for more of an overhang, and put up a fascia board
to support gutters, and I want to add wider decorative trim on the
corners. I want to use tanalised woof for all these things but the
choice of wood where I live is very limited. So I thought I might get,
say, a 3 inch square length of tanalised and use the table saw to cut
thinner lengths. Or I could plane down a 1" thick board....anyway,
would that work? I don't know if the pressure-treatment goes all
through the wood or if newly cut edges would be as prone to rotting as
ordinary softwood.

The local timber yard sells feather edge boards that would be good (if
cut narrower) to make the decorative trim for the corners of the shed.
With that thinner wood (max about 1/2 inch) be pretty much sure to be
treated all the way through?