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post #1 of 8 Old Yesterday, 07:52 PM - Thread Starter
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Soffits?

I'm finally getting around to finishing my framing, and I hit a roadblock: the ductwork soffits...

I was considering 2x4 framing, but I'll lose lots of head space.

I wasn't sure if 2x3 framing would be sufficient? (I know I'd be the same overall height as 2x4s, but I'll save a little on how far the soffit will extend over).

I also noticed some people are using MDF: is this just being used without framing? How far can you span without using framing Behind it?

What width of MDF would I need?

Will MDF bow over time? I know basements tend to be a bit damper than the upstairs...
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post #2 of 8 Old Yesterday, 08:26 PM
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2x4 is probably overkill. check out thesoundproofingcompany.com .everything you ever wanted to know. they have even more info available if you talk to them directly.

here's their thing on soffits. http://www.soundproofingcompany.com/...undproof-room/
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post #3 of 8 Old Yesterday, 08:47 PM
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You can build soffits without any framing under the ductwork. Just span the bottom with drywall and if over 2 ft add a first layer of plywood.
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post #4 of 8 Old Yesterday, 09:08 PM - Thread Starter
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My span is closer to 4 feet. I guess I'll stick with 2x4 ladder framing and traditional drywall.

Too bad. Every inch counts, and this will be quite a span...
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post #5 of 8 Old Today, 04:22 AM
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I framed up my soffits by installing blocking in the joist space, and then notching plywood to fit around the joists, then screwed the plywood
to the blocking. The bottom layer also got a layer of plywood with a bead of construction adhesive (with some nails to hold everything in place
while the adhesive set up). Somewhat fussy to do then simple ladder framing, but I gained inches of space, some of which were given back to
two layers of 5/8" drywall + GG. The first layer of plywood + 5/8" drywall was also given a layer of GG.



So I have to wonder if a similar drop of plywood + construction adhesive between two runs of HVAC trunk would be enough to bridge a larger
soffit and provide with plywood would offer enough support?
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post #6 of 8 Old Today, 05:54 AM
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Quote:
Originally Posted by gizzygone View Post
My span is closer to 4 feet. I guess I'll stick with 2x4 ladder framing and traditional drywall.

Too bad. Every inch counts, and this will be quite a span...
While some may disagree I would span with a quality piece of 3/4 hardwood plywood. Then add your drywall over

I'm talking about cabinet grade plywood.
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post #7 of 8 Old Today, 07:37 AM
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Further to that...

Maybe a few scraps of leftover plywood, in the form of drops in between the HVAC sheet metal runs,
could add some center bracing. A bead of PL3000 construction adhesive and a few nails and you get your
horizontal stiffness and beef up your support.
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post #8 of 8 Old Today, 08:00 AM
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Yes I thought about some drop supports but we need a picture of this ductwork for specific recommendations.
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