I’ve been thinking about wall insulation vs. attic insulation. Why is it that ventilation is not needed in wall assemblies using fiberglass or cellulose insulation in the same way that it is needed for roof assemblies. I certainly know this is true, but discover I’m not clear on the science behind it. For old 2×4 walls, I think it might be because the insulation is thin enough so the dew point isn’t reached within the assembly. But what about double stud walls and other higher insulation assemblies?