My 1930s brick cape has new thermal windows, but I'm sure it's losing a lot of heat through the walls. I suspect there was never any insulation between walls and exterior brick – or else if there was, then it was quite ineffective and probably smashed down by settlement in the space between walls and brick. The walls and ceiling are constructed of an early precursor to drywall – I don't know what it was called but I'm sure some of you do. It is much thicker (5/8" at least) and much harder than modern drywall, and because of that material density probably transmits heat much more, even when it's tightly closing the air space between interior and exterior.
My goal is limited to improvement of just one room because it's a bedroom and is obviously the coldest room in the house. That room has several problems contributing to its coldness: On the north side of the house, has 2 windows, and has a closet backing up against 2 exterior brick walls. (The closet feels like a refrigerator when opened during cold weather.)
It seems clear to me that ripping out walls, installing spray insulation and rebuilding the walls would not make any sense financially. The entire living area of that floor is only about 600 sq. ft. and it's really not an expensive house to heat, overall. But I do need to improve that one room. I envision a low-budget, relatively uninvasive method of insulation and I am interested in getting some feedback.
The method involves a drill, numerous cans of spray foam such as "Great Stuff Big Gap Filler," and a "borescope" (similar to a pipecam and can be had for less than $30) attached to a laptop computer. From that description the general method would be obvious: Drill holes in the wall, spaced out over the entire wall area, and spray the foam in. The borescope rig, which has its own LED light source built in, would help solve the big problem of establishing what's behind the wall already and to observe what happens when you spray a good amount of foam in there – (Where does it fall to? How much does it expand?) – requiring only a series of patchable holes, probably around 1/2". I am thinking, from a few such observations made from nearby holes, one should be able to guesstimate how far apart these injection sites need to be and how much foam might be needed. I also figure that 100% fill would not be necessary in order to achieve a significant improvement. Afterwards, the holes would be filled and finished off. In comparison with any other method I have read about, it would be much cheaper and much less trouble to get the room back to normal.
If you have extensive knowledge of insulation issues, I will appreciate your comments on the proposed method.