Drywall Ceiling parallel to Rafters?

[thomas.jacobs]

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

[dpb]

Don't have a real number, but w/ 16" O/C, I'd not worry w/ 1/2" or thicker. I'd go the parallel direction w/ those dimensions for the elimination of the butt joints and it eliminates the other length-wise seam if use 4x12 the other way. If I do the seam-counting right in my head I get you would have 46-ft edge and 14-ft butts (assuming stagger sheets to not have a full-width butt joint) or 50-ft of edge seams the other way w/ the 4x10's.

The only other thing I'd check is how close the tolerances are on the rafter spacings as if they're just 2x material you only have 3/4" when you split them so there's not a lot of slop for the joints. It also will take getting the first sheet lined up pretty carefully so it stays online going forward as you've got a total of five seams to make work.

[Joe]

Everybody gets all wedgied up about drywall butt joints and its true they often don't look too good even with careful mudding. My technique is make a taper on the butt joint end just like the edges using a small body grinder. Do it outside to keep the dust controlled, then bring the panels inside and hang them. I use fiberglass tape, sometimes two layers, well bedded for strength, and setting type mud. Eliminating extra steps of fill, dry and sand I believe actually saves time and the dead flat joints eliminate problems with things like crown moldings and certain light patterns from windows. The usual caveats of good workmanship apply when dealing with reduced panel thickness. Works on corners, too, where you absolutely, positively, must have a 90 degree angle. HTH

Joe

Joe

[Mark]

If the framer was worth his pay, the joists should be 16" oc and the joints should fall fine. I know that's wishful thinking in many cases, so when you pick up your drywall, grab a few 2x4 as well and if you come across the one joist that isn't at 16, screw a nailer on the side of the offending joist and be on your way.

[Goedjn]

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