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I am putting in a sub ceiling with insulation and drywall. I have begun the project and it kind of suddenly hit me that this weight could be dangerous? I'm running the 2x6x9.5 ft joists from these beams pictured. I plan to do it again on the back section. This is in my garage. Above garage is master bedroom. Middle beam Runs underneath middle of bedroom[enter image description here][1] [Pic1][1]enter image description hereenter image description here

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  • See past answers for explanation of why you want those 2x4's to not be touching the pre-existing ceiling (to keep them from coupling noise from one side to the other).
    – keshlam
    Commented Mar 15 at 3:34
  • There's about a 5 inch gap from ceiling to joist Commented Mar 15 at 3:40
  • That should certainly address my concern
    – keshlam
    Commented Mar 15 at 3:49
  • Any thoughts on the joists going between these 2 beams? Commented Mar 15 at 4:01
  • You should check out the ceiling joist table at IRC R802.5.1. Your design live load strength is 0 psf, and that table says that #2 2x4s are sufficient on 16" centers for your use case, and that's with an unnecessary 10 psf live load capacity. You can shave off some cost and weight by switching to the smaller ceiling joists, although you wouldn't be able to hang lots of weight from the ceiling.
    – popham
    Commented Mar 15 at 4:42

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My quick computation for your added weight is 2.7 psf (neglecting insulation weight).

I would bet that your floor's dead load was spec'ed for 10 psf, so if you have a light floor finish like carpet, then you probably had some unused dead load capacity. For 1 psf carpet plus 1-1/8" plywood plus 2 psf floor framing plus 1/2" drywall, I get a total dead load of 7.9 psf. That hypothetical scenario would leave an unused capacity of 2.1 psf. That hypothetically is enough for most of the 2.7 psf of added weight.

Modern sleeping rooms get designed for 30 psf live load. I've seen a 1991 UBC (the western US's building code before today's national code) calling for 40 psf live load everywhere including the sleeping rooms. Assuming that there was no extra dead load capacity, the 2.7 psf of added weight would imply a live load capacity loss of 7% to 9%. In the hypothetical case of zero extra dead load capacity where the live load capacity is reduced by the full 7% to 9%, the extra dead load could possibly result in some out-of-spec floor sagging over a long time horizon.

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  • Perhaps the OP should have oriented the "joists" the other direction?
    – Huesmann
    Commented Mar 15 at 19:30

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