I have a city house that is over 100 years old and the bedroom has two exterior walls made of brick. Inside the walls are plastered over. Normally, I would just add 2” framing and use polyiso foam. This time under the paneling I see that used 1x3 furring strips and put fiberglass batts. Says it is R9 which is hard to believe being that the furring is actually less than an inch and fiberglass should not be packed.
My question is how much is lost by crushing the fiberglass and should I just replace it with 2” R13 polyiso foam board. Will it make that much more of an improvement?