Interior insulation retrofit
I want to add to the interior insulation in a single story room on the north side of my house in Minnesota. I realize this has been asked before, and would appreciate it if someone can point me to articles that apply, or respond anew. The room in 18×28 and has lots of windows. It was built as an addition 30 years ago, with the construction practices of the time, 2×4 studs, osb, tar paper outer wrap, and oiled redwood lap siding. Bays are filled with rolled fiberglass, covered with sheet plastic, and drywall. I now know that the plastic was not a good idea, but I don’t want to take off the existing drywall, or even consider doing it from the outside. So, are there any big problems with this plan—horizontal strapping screwed through the existing drywall into the studs, 2″ polyiso, tape all seams and outlets, drywall screwed to the strapping, then paneling. If this is workable, how far apart should the strapping be, to be a decent support for the drywall and paneling? I realize there is the issue of thermal bridging from the strapping, and was wondering if there is an insulated product, or if I should just use the lightest cedar 2x4s I can find, or perhaps the issue is negligible in the big picture.
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