This is a 100 year old house - a buy/fix/flip located in Lancaster, PA. I've got crumbling plaster against brick on all exterior walls and lath/plaster on all exterior walls except where I have torn out to expand or modify a space. I will not be studding out the exterior walls. Instead, I am pneumatically nailing and gluing furring strips over all exterior walls (and some interior), insulating all exterior walls with @5.5-R Polyisocyanurate Insulation. Yeah, I know. It ain't much but it's better than nothing. I removed the casements from the double hungs and cut the weights. New replacement windows to follow. Dumb question, but what should I stuff the cavities (where the weights were located) with? As you know they are about 4" wide. Should I first caulk the interior portion of the the cavity that connects to the exterior brick? I got some 23-R craft back insulation that I could cut into strips. Can I use that?
One other thing. I had a privacy violation between two bedrooms. I have since framed what was a door opening in preparation to cover it all with sheet rock. Can't move on to that part until I pass my first framing inspection. What's the best material to stuff into what use to be an entryway between the two rooms that is now studded up? I want to dampen the sound as best I can. The remaining portion of the wall that separates the two rooms is plaster/lathe.