With 4x8 sheets and not counting the seams at the walls, I get
sheet long side parallel to joists, 82' of seam and
sheet short side parallel to joists, 96' of seam.
But you will have to add wood to support the seams, possibly regardless of sheet orientation and joist spacing because
19.5' x 12" or 12.5' x 12"
16" or 24" O.C.
do not equal integers.
Writing a computer program to search for the minimum seam length is probably within the capabilities of an undergraduate Computer Science student.
With drawings you can do it on Excel.
You want 4x12 seam lengths?
Minimum waste/minimum cost is another issue. Draw it out, you'll see.
Last edited by Wuzzat?; 01-13-2013 at 11:57 AM.