Air barriers inside duct chase – GreenBuildingAdvisor

We have a couple of chases where ducts will be running through, and we are confused about air barriers in those locations.

One is a dryer duct running through our primary closet out to the water heater closet (inside the unconditioned garage and to the exterior). The duct is air sealed on the water heater closet side, and the interior walls of the chase are insulated like all of our other exterior walls (R-13 Rockwool).

The other is an HVAC flex duct that passes through the air conditioned space in front of a dormer window. On the attic side, we have R-5 rigid foam board air sealed around the duct. The walls, including the interior of the chase, are insulated with R-13 Rockwool.

Both chases will be drywalled around it (to create a box essentially).

Our insulator mentioned needing an air barrier against the Rockwool inside the chases. However, he only installed it on the flat surface areas behind the ducts and did not install it around the duct entry/exit points. The material they used was DRYLine TSX. For the HVAC duct, he said to just fill the chase with insulation around the duct to avoid needing the air barrier on the sides around the duct.

I have a few questions about this:

1. Is DRYLine TSX an appropriate product for this? From what I’ve seen, it’s a weather barrier. The vapor drive is primarily inwards in our climate, so we don’t want to trap any moisture in these walls/chases.

2. If we need an air barrier on the inside of the chase around the insulation, shouldn’t it also be applied around the duct entry areas as well?

3. Overall, what would you suggest for these chases regarding insulation, air barrier, etc. to ensure we aren’t trapping moisture?

I’ve attached a drawing of both chases.