Hey,

I'm having some HVAC work done and we're rerouting some returns. My buddy wants to use the joist bay in our unfinished basement as the "duct" for part of the return.
The idea is to sheet metal the bottom of the joists, enclosing the bay, and with the subfloor and floor upstairs, it will be airtight.
I've never heard of this. Have any of you?
Is is safe? Functional? a good idea?
Please let me know.
Thanks