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I need to hang some drywall; my ceiling has a couple spots of uneven-ness. There's a few spots that are about 1/4" out of whack and another spot where joists+hanger are a little less than 1/2" down.

It's a normal sized room and the spots that are either bulging or sunken are all located in the same area. I am wondering if that warrants furring out the ceiling or will the drywall flex enough where there's a half an inch level difference?

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Went through this recently myself.

I'd try to limit the joist-to-joist out-of-flatness to 1/8" or less. If it's an obvious part of the ceiling, try for 1/16".

Get a long straightedge and a pile of drywall shims. High joists are pretty easy: add shims to bring them down to flat with the others. Low joists require you to build up the adjacent joists gradually over a few joists to meet that 1/8" (or 1/16").

I attach the shims with staples, but many people like to glue ceiling wallboard in place, to prevent dimples at the screws/nails in the future. If this includes you, then the shims should also be securely glued.

Once you get the drywall up you can somewhat correct ridges and valleys with a repeated skim coats of joint compound. However, it's difficult, messy, and much easier to fix the framing first.

36" Drywall Shims: (menards.com)

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If you have space, you can sister a straight 2x4 along side the joists at the proper height and attach the drywall to the 2x4. That's a good option if you only have a few bad joists. Pay extra attention to the joints in the drywall to make sure everything ends in the middle of a joist. You may end up adding a few extra 2x4's in some places just for nailers.

If you don't have the room beside the joists, or you have lots of problem areas, then strapping also works, run perpendicular to the joists and individually shimmed to the proper height.

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    Of course in an old house nothing is ever square and there's always the question of whether "proper height" means level or constant distance from floor or a compromise between the two. That's actually one of the reasons I'm considering a mock-coffered ceiling in my LR, which is now very oddly shaped -- it'll mask that variation.
    – keshlam
    Nov 4, 2014 at 1:19
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Since your ceiling is so uneven, I would recommend installing furring strips approximately 16" on center perpendicular to the ceiling joists across the entire ceiling. I would also install them around the perimeter of the room. This will even out the waves in the ceiling, and the ceiling will appear to be perfectly flat. If you need to, you can shim behind the furring strip to level it up. It also has the added bonus of allowing you to run wires behind the drywall after it is installed.

EDIT: You can also refer to this question for more tips. What is the best method of hanging drywall on ceiling?

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  • I really wouldn't say the ceiling is "so" uneven, just a few spots. Not sure the furring is worth it.
    – justinw
    Nov 5, 2014 at 5:16
  • @Quoid furring is a fairly standard practice for ceilings because the joists almost never are completely straight, even in new construction. 1/2" doesn't sound like a lot, but it will show in the finished work. You would also have issues if you wanted to install crown molding since the differences in height would be more apparent. If you have a rotating laser level, you may be able to get away with just shimming it since you can see all the high and low spots. You may miss some spots if you are just doing it by eye.
    – Jason Hutchinson
    Nov 5, 2014 at 14:25

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