Supporting Hood Exhaust

skeletron · Dec 16, 2020

What is the most practical way to hang threaded rod from ceiling joists, taking into consideration drywall and attachment accuracy? See the attached for Option A and Option B

Option A: Install new beam, cover with ceiling finish, then locate joists and lag in a Unistrut to the U/S of ceiling into every joist.

Option B: Install new beam, attach clip angle and thru bolt through the side of the new beam. Put a rod coupler on. Attach threaded rod. Make the drywallers cut and patch around rod locations (or...let them run everything flush and then cut out circular holes for the rod).

Option C: (not shown) Similar to either A or B, but run the Unistrut parallel to the new beam.

The application is a hood exhaust in a restaurant. Threaded rods fit to clips on the hood.

Anybody have some suggestions or opinions? Looking for a semi-foolproof way to have this installed with relative ease. Option A seems like the easiest method, but I'm not sure I like it structurally (lag screws into narrow face of joist). Option B is the best load transfer method, but it requires installation tolerance to be bang-on.

Harbringer · Dec 16, 2020

Option A:

You can't lag into the narrow face of a 2x. Make sure you follow NDS edge distance requirements for lags. If the rods are part of your lateral bracing system you need to account for that (loaded edge distance).

Option B:

Looks similar to what I've used in the past but I'd move the attachment to the new beam to the neutral axis. The rod coupler is just hokey. You're overthinking the drywallers job.

Option C:

Seems reasonable if the framing can align.

What is the loading and # of hanger rods?

skeletron · Dec 16, 2020

Ha! Good advice to not overthink it. Also good to confirm my only feelings with existing (Option A) and what I think is logical (Option B).

Loading is for a 10ft hood...there are 4- 1/2" rods

JoelTXCive · Dec 17, 2020

I see the 'roof side' note on your drawing. Is it roof immediately above, or do you have a little attic space above?

Also, approximately how heavy is the vent hood? Have you seen ceiling fan electrical box mounts that spread out between joists. They can support ~50lbs a piece. Maybe something could be done with them?

skeletron · Dec 17, 2020

Roof is directly above (there's strapping)...so unfortunately I can't sling a Unistrut overtop, which would have been my first go to solution.

Interesting thought with the EE box mounts. I think this unit might be too heavy, but there is a smaller one that I'm looking after as well.

Harbringer · Dec 17, 2020

For supports between joists just add 4x4 blocking and your rod can be thru bolted. Those ceiling fan boxes are flimsy and cost more than wood blocking.

jayrod12 · Dec 17, 2020

If you're putting in a built-up, or solid, PSL to support it, I'm a big fan of option A. You most certainly could get some self drilling lag screws into the narrow face of an LVL. Reduced capacities but should still be plenty. GRK screws or MTC screws are higher capacity self drilling screws for lumber. I believe simpson has similar products as well.

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