20x30 single story foundation

[Mike A]

John, Going to the mountains to see if the snow is gone so we can lay out the post and pier foundation. My question is, beams should be spaced @ 20' outside edge to outside edge correct? The 2x12 floor joists should be cut to 19' 9" to allow for the rim 1 1/2" on each side or does the rim over hang the beams with 20' floor joists? Hope I'm making sense here. Everything down here in the valley is slab on grade and I have never seen a wood foundation. Thanks.

[John Raabe]

You want the outside of framing to be 20' wide, so yes, you will cut the joists down for the rims. (Framing dimensions are before any sheathing.) This dimension isn't quite as critical for the beam placement, but I designed them to align with the wall and floor framing so plywood or metal straps could be nailed to all surfaces and thus tie the elements together in a synergistic structural unit.