Ceiling Soundproofing Question

[MikeInMilwaukee]

I'm having trouble figuring out how I could drywall the inside of that soffit, and make the drywall extend up to the subfloor in each joist bay.

Not that I don't believe you, but is there any documentation that says it's illegal to hang framing from channel? I haven't found any. It's not just a matter of staying within the weight limit of the total # of clips?

[MikeInMilwaukee]

Bump.

[Soundman2020]

I'm having trouble figuring out how I could drywall the inside of that soffit, and make the drywall extend up to the subfloor in each joist bay.

It's a lot of hard work, yes, but if you want proper isolation then that's the easiest way to go. You do have to completely surround the duct with enough mass to continue the envelope of the outer-leaf. Id would suggest doing it with plywood or MDF, which won't crumble like drywall if you need to wiggle it a bit as you install each piece for a tight fit around the joists.

but is there any documentation that says it's illegal to hang framing from channel?

Show your design to your local building inspector, and ask if it is allowable under code. Also show it the manufacturer of the resilient mounts, and ask if that is an approved method for using their products.

- Stuart -

[Zenon Marko]

I understood what you were saying, but it won't work like that, and would not even be legal. You cannot hang framing from clips, to start with, and you also need to create a two-leaf system AROUND the duct.

Here's how to do it:

soffiting-ducts-8.png

As I said, you need to enclose the duct in drywall first, such that it is no longer inside your MSM cavity.


- Stuart -

This is excellent. Thank you for posting this, Stuart, as I am in a similar situation (Home Studio in NYC) , with a lot of noise-producing and noise-conducting building pipes and ducts cutting right across the inside of my live room. I want to "soffit" those away.

I see the challenge of attempting to add the drywall (or alternative) inside the framing.

How well would this system work if you put the drywall outside the framing? It seems that would then require an extra frame to attach the clips, hat channel, and inner skin, and of course the air gap is reduced.

Or: What if the outer leaf were a plywood box around the duct (pipes, etc) instead of framing+drywall? Then for the inner leaf, build a metal or wood frame spaced a bit away from the plywood, with the clips, channel, and inner drywall?

[Zenon Marko]

but is there any documentation that says it's illegal to hang framing from channel?

Show your design to your local building inspector, and ask if it is allowable under code. Also show it the manufacturer of the resilient mounts, and ask if that is an approved method for using their products.

- Stuart -

I was researching solutions online.
Kinetics offers a different type of clip, "Unibrace", which seems to be shown here supporting the frame. (I have no affiliation or experience with this system, and thus cannot vouch for the safety or local code compliance thereof!)

Kinetics - Isolated Soffit with Unibrace Clip

[Zenon Marko]

Here's how to do it:

soffiting-ducts-8.png

As I said, you need to enclose the duct in drywall first, such that it is no longer inside your MSM cavity.

Does this create a triple-leaf effect at all?
(inner leaf + outer leaf around duct + floorboards above duct?

Or is that a necessary compromise, with nevertheless better transmission loss than an alternative 2-leaf like the one originally proposed?

Thank you for any clarification...

[Soundman2020]

Does this create a triple-leaf effect at all?
(inner leaf + outer leaf around duct + floorboards above duct?

Yes, it does create a 3-leaf system for that area. But you don't have much choice.

Or is that a necessary compromise, with nevertheless better transmission loss than an alternative 2-leaf like the one originally proposed?

Correct. It's one of those "necessary evil" things. It would be nice to avoid, but there's no other options, so you have to do it to get the benefit you want. And since it does create a 3-leaf situation, you have to take the usual precautions to deal with that: more mass on the leaves, and larger air gaps.


- Stuart -