Sheetrock over 24-inch centers


I am insulating and finishing an attic space. The sloping roof rafters are 24 inches on center. Between the rafters, I will be placing rafter vents and insulation, and then sheetrock over that.
My question is about the thickness of sheetrock that I need to use. I think that 1/2-inch sheetrock is probably too thin for rafters that are 24 inches on center and would tend to sag.
One option is to use 5/8-inch sheetrock.
Another option is to double-rock it with two layers of 1/2-inch sheetrock.
Any suggestions as to what would be the best way to go with this? -- 5/8-inch, double 1/2-inch, something else?
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1/2 inch will work on 24" centers. If the insulation is heavy you can go to high strength. http://www.nationalgypsum.com/submittal/09%2029%2000-06.pdf
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Be sure to put the sheetrock perpendicular to the rafters. The place next door to me, which I bought a few years ago, has a 16x20 den that was added, and the ceiling was installed parallel to the 24" oc rafters-- it looked like a washboard. It had been vacant for a while and the roof leaked so a lot of the ceiling was laying on the floor by the time the deal was closed. I ripped the rest out, added 2x4's between the rafters, so I actually had 12"oc, reinsulated and put the sheetrock the other way. For an amateur, I think it came out pretty well-- looks 100X better than it did. BTW, both old and new SR were 1/2". Larry
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Lp1331 1p1331 wrote:

Yep, there is a grain with sheetrock, and it is longitudinal with the "long" axis as your observations bear out.
Jon
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Horse Hockey....Go buy a couple of bundles of Fur Strapping and run it 16 OC..It isn't that expensive and will make a world of difference in the ease of installation of the drywall and the look of the final product.....If you don't you will forever be dealing with popped screws and cracked butts..As a pro I will NOT do a ceiling with no strapping as I can't guarantee it because it WILL have problems and look wavey......HTH....
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If it was me- I'd put fir-strips across the rafters on 16" centers and squeeze in a couple extra 'R's with that foil-faced bubblewrap. [Or, if it was in the frozen north or boiling south, I'd run 2x4's on edge & add 3 1/2" of insulation.
You did allow for air circulation under your roof boards, right?
Jim
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wrote:

Yes. The "rafter vents" I originally mentioned are called Durovent, and I am using them for air circulation.
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SOMETHING ELSE: They make a STIFFER ceiling board..get it from a REAL sheetrock distributor..not BigBox store
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