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So I noticed that my 1961 year old one floor home joists are not even, some areas it's bowed down. I ran a string line, I see about 1/2 inch low points in few areas.

I have read the standard fix to this is strap the ceiling with 1X3 straps, perpendicular to the joists at 16 on center.

If I do not want to have perpendicular straps crisscrossing my ceiling, can I level the ceiling by attaching 1/2 inch Birch Plywood strips, attachedenter image description here along the joists (not perpendicular), and shimming where necessary? Thank you. Alex

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Sister with steel stud using a lazer. Lazer a line across at your lowest point and sister on the line. Steel stud will stay come straight, stay straight throughout the installation and after the installation. It's easy to notch around existing obstacles and easy to work around with anything new going in.

This is actually a perfect example enter image description here www.finehomebuilding.com

If you don't have a lazer a string works well too.

  • Thanks Joe, it would be great to see a picture. Would the steel studs ran right next to each joist? And drywall is mounted on them, not the joist? – alemiss Mar 4 at 1:24
  • So after that, the drywall will be screwed to the metal studs, correct? – alemiss Mar 4 at 2:28
  • You got it! You just need to make sure the drywall has a place to hit, as with any other leveling method. This method also allows for pipe, duct and any other long items to be placed in the ceiling cavity with ease. Perpendicular furring channel or lumber makes it hard to run anything in the cavity and drops the ceiling more. Furring perpendicularly with wood gets really hard when tapering to zero and sistering with wood makes you have to deal with the bows and crowns of the wood. – Joe Fala Mar 4 at 2:48
  • The space available for screwing drywall is 1.125inch thick. How can two drywall panels butt up in this small space? For a wood stud, it has 1.5inch of space, but metal stud as only 1.125 or max 1.25inches. Wouldn't that be a problem? – alemiss Mar 4 at 4:06
  • You only need an inch for the drywall seam. 1-1/4 is plenty. – Joe Fala Mar 4 at 12:17
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Not unless you get lucky. Or use a "drop" ceiling of some kind.

If you have a small area that is out of flat, then yes, you could put a lot of shims into that small area. If you are not using drywall, but some kind of dropped ceiling, then the joists don't matter at all and you can ignore them.

But if (as is likely) the joists have become wildly out of flat, and you're planning to put up a drywall ceiling, ask yourself: how am I going to fasten the drywall?

Hanging drywall, and possibly insulation of some kind, from the ceiling means you will have a limited selection of places to fasten the drywall. Trying to rely on some tiny "islands" that you have shimmed down will make the support even weaker and more likely to sag or bow.

The reason for crossing the joists with furring strips is so that you can shim above the strips to get a flat surface, then fasten the drywall to those strips at whatever interval you are comfortable with. Having done this same job a few years back, it's not as hard as you think, and it beats a lot of the alternatives.

Be wary of how you determine "flat", though. A string is a better option than a level. The ceiling doesn't have to be perfectly level. It just needs to be flat.

  • Thanks Austin. The plywood strips will be nailed to the joists for the entire length of the joist, not just in some few locations, or islands. And since the plywood is only 1/2 inch thick, when I fasten the drywall, the screw will actually go past the plywood strip and into the joist itself. Isn't that sufficient? – alemiss Mar 4 at 1:13
  • As long as the strips are rock solid. Put in lots of shims, about as often as you intend to screw the drywall. – Austin Hastings Mar 4 at 2:23
  • I get your point. It's not as feasible as I originally thought. May be I'll try sistering with metal studs, if that doesn't sound feasible either, I will suck it up and do strapping with 1 by 3. I really didn't want losing a whole inch of ceiling height and also have crisscrossed ceiling under my sheetrock. Thanks again. – alemiss Mar 4 at 5:07
  • To expand on Austin's answer, a hybrid solution between a "drop" ceiling and drywall with furring strips is using the USG Drywall Suspension System (or similar). It's basically a dropped ceiling grid with no acoustical ceiling tile, but with drywall screwed to the grid instead. This is the commercial way we would do it to achieve a perfectly flat ceiling. In commercial, the ceiling height is 5-15 feet below the floor/roof above so we cannot use furring strips (and fire code issues beyond that). This will probably be too expensive for you, but it's an option. – Dotes Mar 4 at 13:57

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