I have a 100 year old twin that has plaster walls directly on brick.(no studs or fir strips)the rooms are small i would prefer not to lose much floor space.i am considering putting 2x4 on the flats and using spay foam or a normal framed wall with fiberglass. I don't want to mess with the exterior since i love the brick. Should i be worried about moisture? Should i let it be? Should i just sheetrock over top? Any thoughts or ideas?