How to mount 4″ round ceiling box with strapped ceiling
This is the first time I’ve ever strapped a ceiling. I did so because I used 3/4″ osb on the exterior walls (and interior) to tie my exterior air barrier (Zip R4) to my ceiling air barrier (drywall). I’m about to start wiring and I’ve realized that due to the strapping, I don’t know what 4″ round ceiling boxes to use that I can mount to the trusses so that I can have enough clearance for 3/4″ strapping plus 5/8″ drywall. I found this box by Arlington that is adjustable up and down, but doesn’t have a vapor flange: http://www.aifittings.com/catalog/specialty-boxes/in-out-box-for-ceiling-fixtures/
Then I found this from Arlington that can be added to the above for air sealing to the drywall: https://www.aifittings.com/landing/vbr1
Together, these are going to be a $25+ each setup. Is there something simpler that can be used? Like maybe just a normal vapor box with a longer metal bracket so you can just drop it down further and screw it in? I know everybody out east straps their ceilings, so there has to be a simple solution I’m missing.
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If there's no junction in the box you can just use a pancake box flat against the ceiling.
Our vapor tight boxes come with a tall flange so you can mount it on the rafter but space it down 3/4" to be flush with the drywall.
Looks like Carlon has something similar, search for FN-CFB. I think there is also one that mounts onto 2x4 on flat. You can set the 2x4 at the proper height.
My electrician said on the box he uses (with sliding mounting bar), the bar can be flipped allowing him to drop it 3/4" and still mount in the meat of the truss. So I'm just going to let him use what he normally uses, and then add these to each one. They're super cheap at around $2. Madison Draft Seal Kit PN: MDSKRC
They're pretty widely available. Have you ever used them? I wonder if I should still add some caulk around it before sliding it on?
Why are you not mounting the boxes on the stapping plane? You can attach a piece of 2x4 on top for fastening purposes