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I saw a YouTube video advocating that an interior, non-bearing wall is well constructed with a 3/4" gap between its top plate and the ceiling joists above it. Is this legit or not? I've been watching a bunch of DIY youtube videos to frame out and finish my basement. House was built in 1940 with original wood and concrete in the basement. Do concrete slabs really expand enough to make the hardwood floor above bow?

I've seen a lot of threads on here saying there shouldn't be more than 1/4" gap between the top of the frame and the ceiling joists above. For reference: I live in the Midwest with pretty cold winters.

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  • If a concrete slab expands that much, you probably have much bigger problems, than leaving a gap between wall and floor.
    – crip659
    Commented Oct 14, 2023 at 15:59

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It is common for framers to leave a gap between the top of a partition wall and the upper anchor point. (truss cord or floor joist).

If you buy precut studs, they are sized to give a 3/8" gap.

The reasons, over the years, have been; expansion, contraction, compaction and simple ease of setting up the wall.

In my area (SW fla.) 3/4" is a little excessive, 1/2" to 3/8" is more common. However a gap of 3/4" would not make the wall a candidate to be redone.

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  • Her video shows a perimeter wall. Do you worry about squeaks developing in places with the ceiling is more flexible?
    – popham
    Commented Oct 14, 2023 at 15:38
  • Squeaks have never been an issue.
    – RMDman
    Commented Oct 14, 2023 at 23:55
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He's probably trying to save face with his customer. To avoid the pinch when standing the wall up, often people will make the frame 1-1/2" short, stand it up, and then hammer a second top plate into the gap above the wall.

When you install a fastener across a big gap like that into the ceiling, the fastener resists horizontal loads in bending (weak). As the gap shrinks, the fastener starts resisting the load in shear (strong). It's pretty easy, I think, to anticipate that the closed gap is much stronger than that 3/4" gap.

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