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I am currently finishing an older 3-car detached garage. Both the wall studs and the ceiling trusses have 24" OC spacing.

I know that for the ceiling, I'll need to use 5/8" thick drywall, due to the 24" spacing, and sagging that would occur over time as moisture hits the drywall (which will happen in a detached garage). However, for the walls, our local code allows for 1/2" wallboard for 24" OC studs. But wouldn't I have the same issues as with the ceiling? Thoughts? (I am not opposed to the price- it is only about $30 difference to use all 5/8". However it is easier to hang 1/2")

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2 Answers 2

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You actually have a couple of options in this case. The easiest option would be to simply use 12 ft sheets of 5/8 fire rated sheetrock and rent a lift to do the ceiling with. A lift is very easy to use and almost makes it a one person job. Personnally, I'd also use 5/8 on the walls as well. As BMitch already mentioned, mount the wall sheets horizonally and stagger the vertical joints. You can use 2X4 nailers, (fire breaks) at the 4ft OC point, but not really necessary. You will not see any bowing or cupping with 5/8" at 24" OC on walls.

The second, and BEST option would be to install 3/4" strapping 12" OC across the field of the ceiling, and around the parameter. This will give you a lot more surface area to screw the drywall to and make aligning joints a lot easier, especially if the 24" joists are not perfectly spaced or square. Putting up strapping is quick and easy if you have a nail gun. Use 4D ring nails. Ring nails will hold tight and not loosen over time.

Hint: Use a chalk line on rock to mark backer locations before you hang it, or you can also mark the location of your joists or strapping on the wall before you lift the rock into place. Secure the rock with a few screws to hold it in place, then use the marks to snap a quick chalk line marking the location of your strapping. This will assure you hit a solid spot with every screw. Ceiling screws should be no more than 16 inches apart.

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+1, lots of great points. @MarkD, if you don't go with the strapping idea, any joists/studs that aren't well aligned for the end of your drywall can be worked around by sistering a stud on the side you need it. On the ceiling, I'd extend any sistered joist all the way between the two load bearing walls to add structure. –  BMitch Sep 20 '11 at 2:15

5/8" drywall will work on the ceilng, and in a garage, I would want to use fire rated even if it isn't required in your instance/locality. You can also get 1/2" sag resistant drywall that is specially designed to handle 24" OC ceiling joists, but I can't find it at the major HI stores online, so this may be a special order.

For the walls, you shouldn't have the same sagging issues as the weight is pulling the drywall to the floor rather than away from the wall. In that situation, the drywall is under a lot of compression force, which it handles well. It's the expansion that drywall doesn't do well with, which is why it's easy to break when one side of the paper is cut.

If you are paranoid about this, then install a fireblock (a standard 2x4 installed horizontally between two studs so that fire cannot freely burn up the wall cavity) in your walls at exactly 4' from the ceiling and use that to give extra support to each piece of drywall and make a stable connection between the two sheets. With 24" wall spacing, my concern is structural, so assuming the current design passes code, I would install the drywall horizontally to connect the maximum number of studs together.

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