Adding insulation to Superior precast walls – GreenBuildingAdvisor

Hello all, when I built my house I used Superior Walls precast/insulated walls.  These are essentially a panel with a 1.75″ thick concrete shell and a 8″ deep concrete “stud.”  Essentially a stud wall made from concrete with 2.5″ wide studs.  They insulate the cavities with 2.5″ polyiso and then the “studs” and top plate are all covered in 1″ EPS.  I’ll try and add a picture here in a bit…

I’d like to add insulation to this.  My above grade walls are R44, so these basement walls are not great.  I have more of the basement poking out of grade than I initially anticipated as well.  When I calculate the true R value of the superior walls, I come up with ~R13.  There are 6″ deep, 19.2″ cavities I could fill.  But the studs and top plate are the real killer, terrible thermal bridges.

I am looking for some suggestions on the best way to go about this, on a diy budget.  I can get 19.2″ batts from lowes (harder to find than I thought).  And then I was thinking 1.5″ paper faced Polyiso over the whole wall.  Strap that with 1x3s for drywall.  The polyiso would solve the thermal bridging issue.  I’m not sure if I’m creating a moisture issue with the sandwich of fiberglass in the cavities.  I’d rather avoid filling all the cavities with foam.  I can get reclaimed polyiso fairly cheap, but cutting it all up would take forever.

Alternatively, I could cut the polyiso into pieces to cover the sides and face of every stud, then just fill the remaining cavity with fiberglass.  The foam would not be covering the fiberglass in this case.  But a lot of cutting involved.

I’d be interested to hear some thoughts or experiences.