Oren Leiman , nice to see you here! I agree that this situation requires careful thought and assessment before moving forward. These walls have been sitting there for 90+ years, with heat from the interior freely moving through open wall cavities and drying out the backside of a potentially leaky stucco assembly. Blowing insulation into these walls will reduce heat transfer (and air movement behind the stucco assembly) and could cause moisture issues. But it also could be fine... can you tell us more about the situation: 1) what's the integrity of the stucco? does it have a coating? 2) any evidence of interior moisture damage, especially at windows? 3) have you done any exploratory testing to see what things look like from the inside?

Thanks Katy!
No obvious leaks from old stucco. Major renovation begins in fall.

In New England, USA, i put vapor barrier behind sheetrock during ac remodel. …, 30 years ago