How Long Does It Really Take To Insulate A House?

Yeah, old houses can be a real puzzle. I’ve seen folks go all-in on spray foam or blown-in cellulose, thinking more is always better, but sometimes you just end up trapping moisture where it shouldn’t be. Ever run into those weird hidden cavities behind plaster walls? Sometimes you open one up and it’s like a time capsule from the 40s—old newspapers, random junk, even the odd mouse nest. Curious if anyone’s tried those vapor-permeable insulations in older homes... did it actually help with that musty smell?