u/Rickymcraft

Context: I am US-based in the PNW, Western Washington, in the South Sound.

I am planning to build a 24x16 shed, and running into some questions with the raised foundation, so I wanted some pointers:

1. With 4 single 2x8 girders, 16" from edge, 60" span, and 3/4 TG sub-floor, with the joists at 16" OC, is it still necessary to use 2x8 for floor joist? It will be used as a backyard office.
2. The posts and the beams will be PT & GC, but is it necessary to use PT for the joists as well? It is going to be about 19-20" off the ground.