I live on the gulf coast, zone 2 hot/humid.

Current project is finishing the attic of my old house. It’s a duplex, and the attic goes across both sides of the building.

The central AC system for the first floor units is old but functional and the ducts go through the previously unfinished attic. Drawing #1 attached. The ductwork is not in great shape, insulated and wrapped with plastic with lots of tears and dirt.

We are finishing the larger front part of the attic, but not the back part where the units are. The insulation plan for the rest of the space is a vented assembly w/baffles behind batt insulation going up a ridge vent.

We dont have the room air conditioned yet but it will be, with a window unit.

The issue
A portion of unit 2’s AC duct goes through the space we are finishing. It has been suspended from the inside of the roof sheathing. At first, we framed out a cage around the duct and put in insulation – as if it was just another part of the wall. Within a day, the insulation we put around the duct was very wet with condensation. See pic #2.

We don’t have the budget/knowhow to install minisplits for unit 2, or room to run the duct work in between the floor of the attic and the ceiling of the first floor. The duct has to go through this attic room somehow.

The questions
– My thought is that condensation formed because we ended up with a moisture barrier in between two layers of insulation? (cold inside of duct — insulation — plastic wrap — [water!!] — more insulation — ungodly hot) Is that correct?
– Can we replace this duct with another that isn’t insulated, then put our own batt insulation up around it? How do you ensure that insulation around a duct doesn’t get wet?
– How would you recommend hiding a duct in a bumpout in this situation?
– The duct will go from the unconditioned, unfinished back part of the attic, through to the conditioned, finished portion. How to seal the place where it transitions between the two?
– The rest of the attic is rockwool and rigid board, but I guess we could do blown in or spray foam in this one section?

All help appreciated.