Insulating basement foundation walls with dryer vent?

Question

I have a basement wall that was framed but never finished by the previous owner. I would like to complete it but want to be sure I’m doing things correctly.

From what I can piece together I should be using foam board (but getting some mixed messages on if EPS or XPS is better) directly on the poured foundation. Then more foam board used to insulate the rim joists (with proper sealing around all of this).

I’m zone 6. If I’m understanding things correctly, no vapor barrier is needed if I use 2” foam.

What I’m stressing over is there’s a dryer vent behind the studs. What is the best way to handle that?

The vent is 4” so even with the foam there will be a space between the studs and the foam board.

Do I put the foam up to the dryer vent and do something different in that area? Just fill all the open space with rockwool?

I think without the vent I have a pretty good handle on what needs to be done, but the vent is kinda freaking me out and I want to be sure I’m not doing a critical step wrong.

I added a couple pictures, but any help would be really appreciated. Thanks so much for anyone that has some input!

Answer 1

(I'm gonna leave the insulation question alone.)

There are several approaches to the framing. There may be more I can think of 3 basic ideas:

1. What you show, basically building a wall in front of the duct.
2. Notching out the studs for the duct so that you only have about an inch of wood. This sets the wall back 2.5" compared to the "in front" method. You don't need studs here to be full thickness, because the wall isn't structural—it's just something to hang the drywall on (just be careful not to drive drywall screws into the area where the duct is).
3. Build a chase for the duct. There are a few different ways to do this. You could shift the duct out from the wall by the width of the studs, then build the studs behind the duct, boxing out the chase at the top. Or you could shift it less, and notch out the tops of the studs so that the duct kind of sits in the notch. The chase will protrude less, if that matters to you.

I prefer Option 3, because that saves valuable floor space. If you build the wall in front of the duct, you lose floor space equivalent to the diameter of the duct or more. You can see this "dead" space in your last pic.