I am remodeling a bathroom and adjacent room and walls that are on the exterior side of the house are now open. I am trying to figure out what I should do to help insulate the walls better. The house was built in 1951, located in the temperate CA Bay Area and has a stucco exterior. It looks like the walls are made up of a dark fiberboard for the exterior sheathing. The studs are a little strange in the rooms. It looks like they are 2x4 with additional strips to get it to something like 2x6 and then some more strips that were used to attach the wood panel wall to and were probably necessary to clear the footing on the foundation slab at the bottom of the wall. These additional strips are often thicker than the underlying 2x4, so the cavities are not a uniform thickness. Is there a simple guide to what retrofits can be done to insulate the wall? I am thinking of using Roxul insulation. Does it need to fill the entire cavity depth-wise? I would also probably go with drywall for the interior sheathing.
The room is on the first floor and in the summer it generally stays cool. I am guessing in the winter it will get a bit cold since it stays so cool in the summer.
On the bedroom and bathroom walls there are windows. These windows are original steel casement windows. I have done some research on windows and am not sure if replacing them would really be worth it, especially since I like the fact that the steel frames are really thin. I was wondering if maybe I retrofit them with laminated glass with low-e glass I could get some efficiency boost and sound/security benefit without tearing them out.