I'm renovating a single-family basement. The floor joists above the basement are 2x8 douglas fir, mostly spaced 12" OC. The basement ceiling will be finished with a single layer of 1/2" drywall. There's no requirement for fireproofing or soundproofing, and it's not an earthquake zone.

The joists in the ceiling are not sufficiently level for the finished ceiling. So I'm considering sistering those joists with steel studs, which I'll install level. I'd then attach nominal 1x4 strapping to those steel studs, and attach the drywall to the strapping.

My question is about the spacing of the steel studs:

  • If I sister every joist with a steel stud, then the steel studs will cost more than I'm willing to spend. I'd just use shims at that point.

  • But if I only sister every second joist with a steel stud (i.e., the steel studs will be spaced 24" OC), I'm not sure if that will provide enough points of attachment for the wood strapping. I.e., I'm concerned there's a risk of the strapping partially or fully pulling away from the steel studs, resulting in a ceiling failure.

Anyone know if I can get away with the 24" spacing on the steel studs?

Clarification: The wood strapping would be installed perpendicular to the steel studs and spaced 16" OC. And I'm using 4'x8' drywall sheets. So if I sister every joist with a steel stud, there would be (on average) 24 steel-to-strapping attachments per drywall sheet. If I sister every second joist with a steel stud, each drywall sheet would, on average, be supported by just 12 steel-to-strapping attachments. If we conservatively assume 40 lbs per drywall sheet, then we're looking at about 2 lbs vs. 4 lbs of static load per steel-to-strapping attachment point, respectively.

  • What's the point of the strapping if you already have a level ceiling at that point? 1/2" no-sag or 5/8" drywall span 24" just fine. – isherwood Apr 3 '19 at 14:47
  • The reason for strapping is to give me a wide backing surface for the drywall, to make screw placement easier, especially at drywall butt joints. I've hung ceiling drywall onto steel hat channel in the past, and the degree of precision required for screw placement at butt joints was a real hassle. – Christian Convey Apr 3 '19 at 15:11
  • That's a fair point, but I'm not sure the net expense and effort savings is there. You might just double up the backing at butt joints. – isherwood Apr 3 '19 at 15:15
  • @isherwood: By "double up the backing", are you saying that I should use additional steel studs in the vicinity of drywall ends, so that I don't need to screw both sheets of a butt joint into a single steel stud? – Christian Convey Apr 3 '19 at 15:21
  • Or wood. Whatever's convenient. You could also float your butt joints and use 1x4 there. – isherwood Apr 3 '19 at 15:32

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