HVAC Ducts Do Not Fit Anymore?!

[christophercarr86]

Hey everyone, I am currently building my RWAR in our basement. I added 3 layers of 5/8" drywall to the underside of the subfloor of the kitchen above between the joists. This took up an additional 1-7/8" of depth in those joists. Now the existing ducts for the rest of the house that run through that ceiling no longer fit. Them being 2" lower now there is wiring for the house that is in the way. (I attached 2 pictures for reference).

These are only 2 ducts that run from mechanical room to other areas in the house. They do not penetrate the studio. My plan was to replace these sections that run through the studio ceiling with flex duct so that I can squeeze it over and under the wires as needed.

Any other suggestions to get these ducts back connected ?
And any pros/cons for using the flex duct in the ceiling ? Will it help with isolation too ?

Thanks in advance!
Chris

[gullfo]

the flex duct can be useful to decouple them from the structure, however, "squeezing" the flex duct can result in reduce hvac performance, noise (wind velocity increases), etc. one option is to go with smaller hard duct decoupled to address the increased velocity in a consistent manner, wrap as needed to damp the vibrations etc. another option is to find better ways to move the wiring to accommodate the ducts.

[christophercarr86]

Another thought I had for a different option was what about if I lower the hvac ducts that run over top of the studio?

Since I am building a room within a room, the ceiling is coming lower enough to accommodate that lost 2". Would there be any sound isolation issues with the hard duct straddling partially in the outer ceiling and inner ceiling ? It would only be touching the outer ceiling.

[gullfo]

that would be fine. remember to damp the ducts if they're hard ducts to reduce any noises from the resonances of the duct, and also it would be wise to investigate internal controls like fins/vanes in curved corners to reduce turbulence noise.

[christophercarr86]

Would it be beneficial at all to replace the hard duct with insulated flex duct (still running straight) but to assist in the dampening of them ?

[gullfo]

if flex duct is an option without compressing it too much, then that should be ok.

[christophercarr86]

Awesome, I was planning on replacing as much ridged duct work as I can with flex for sound improvements. They will all be approx 10' runs, nothing crazy. Just some HVAC guys are concerned with servicing/cleaning flex duct, or potential damage if a rodent ever got in, stuff like that.

The flow seems to be very comparative, I was mostly focusing on any potential benefits to stopping any extra bit of sound getting into that duct work.