On 2 Jan 2007 08:45:58 -0800, wrote:

23'x10' ceiling on three-season porch with rafter's 16"OC.
Help me understand. Everything I read says that I should run the
sheets parallel to the joists for strength. I can do that by
minimizing butt joints using 4x12x1/2 sheets.
I can avoid butt joints all together by using 4x10x1/2 sheets parallel.
I have checked the nailing edges and they fall on rafters. What am I
giving up strength wise running parallel to rafters? What else
haven't I thought of yet? Thanks tom

That seems strange to me, since everything I've read (which
admittedly isn't much) says that you'll get less sagging
if you run the sheets perpendicular to the joists, so that
each panel spans as many joists/rafters as possible.

--Goedjn