So I'm trying to finish my basement. I have a conundrum as to how to build a wall under a soffit. Here's my situation - I have an HVAC duct that is running really close to the wall - like maybe 1.5" or less. I need to build a soffit around the duct AND build a wall under that soffit. Is it possible to attach a wall to the soffit? I was thinking that I could build a U, with a PT 2x4 on the back side (if it fits) and attach it to the joist at the top and to the wall at the bottom. I could then use regular 2x4 to build the rest of the U and attach the wall to the soffit. That doesn't seem like it'd be super stable How would I insulate behind the duct given that I might have less than 1.5" to work with?
Update: I measured on the open end and it looks like I have about 1", maybe 1 1/4" max, between the foundation wall and the duct.
Update 2: Not sure what pictures you wanted added, so here's 2. The first is the end of the duct line, the second is looking back at the duct running all the way back to the unit.