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I’m considering putting up 1x3 strapping (rather than steel beams)to level the ceiling in my kitchen (century home) before putting up rock. It is out of level between the joists anywhere from 0 to 1/8” to 1/4”. The joists run between 14”, 16” and 18” OC. The ceiling area is about 390 sf. So my main question, that I can’t find in the building code, does this meet code in a kitchen. I guess one of the main concerns is around fire code.

Also, I’d like to use 1/2” fire rated rock rather than 5/8

This is in Ontario, Canada.

(Those scabs you can see was the original builder attempt to level them)

An added question, how out of level is acceptable to not be visible?

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  • The visibility depends mostly on the angle of the lighting. Secondly on the rate of change as 1/4" over ten feet is not 1/4" over 8", which is why seams are mudded with a very wide knife and cheap builders prefer completely flat paints rather than satin and spray texture. For surfaces with strongly parallel lighting, smooth finish, and semigloss paints the solution is usually a complete coating of hot mud with a long straight edge and lots of sanding.(hot mud doesn't shrink much so far fewer coats are needed) – Max Power Apr 18 '20 at 21:14
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Not a full answer, exactly, but enough additional comments to the answer by @Ack that I thought I could get away with it.

Just to reiterate, you don't need fire rating, unless the kitchen ceiling happened to abut a different unit within the house. Then I'm not sure.

1/8" - 1/4" out of level is pretty subtle. It would be noticeable if there was crown against the ceiling, or if your upper cabs were close. It would also be noticeable if it was 1/4" inside a couple of joist bays. If you didn't strap the ceiling, you could fix the cabinet/crown problem with mud.

Here's an answer I wrote a while ago about strapping ceilings. (Paradoxically, it wasn't the right answer to the question, but it fits your application.) SE answer on strapping ceilings. Strongly suggest you lay hands on a laser... I'm not going to go back and edit my old answer, but at this juncture, I'm not sure how I'd do this efficiently with a level. And definitely use 1x4s. They won't cost much more and give a lot more wiggle room for seams.

Edit, to your additional question, "how out of level is acceptable to not be visible?"... If you have crown up against the ceiling, or upper cabinets within 1", I'd say you want to be within 1/8" for the whole ceiling. If you don't have that situation, I'd shoot for 1/8" within any given 3' span. (It really isn't hard or time consuming to get a ceiling dead flat...)

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    I up voted this as it definitely adds new and helpful info. I feel like this is one of those times that two answers are both on target and I want for a way to combine them and show co-authors (different from editing someone else's post) – Ack Apr 18 '20 at 17:37
  • @Ack -- sometimes folks will roll comments together into a community answer. I'm generally happy to have multiple people respond and add extra info. (And I'm usually a bit tetchy if someone tries to edit my answers beyond simple grammar/spelling.) – Aloysius Defenestrate Apr 18 '20 at 19:02
  • I feel the same about the editing, of mine or to others, I don't want to mess with someone else's words. The community answer, do they give credit to all the contributors? This comment section is probably not a good place for me to ask about it. – Ack Apr 18 '20 at 19:06
  • Folks in meta might have opinions about this... – Aloysius Defenestrate Apr 18 '20 at 19:08
  • That is irony not paradox. – Max Power Apr 18 '20 at 21:00
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Fire rated sheathing is not required anywhere inside a residence with the exception of the garage.

It is fine to use 1/2" drywall on spans up 24" oc if you place it perpendicular to the supports, and up to 16" oc if applied parallel to the supports.

Using wood shims is just fine and common.

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