Rockwool outsulation: How does the condensate get out?
I lived in Maryland, mixed-humid climate, and am thinking of a retrofit strategy for my solid masonry house from the 1930s.
Since I have plumbing between the 2-wythe brick and the plaster, and for the sake of keeping the thermal mass inside, I am thinking of the PERSIST strategy of wrapping the outside of the house with Grace Ice & Water Shield (the roof also needs replacing, so overlapping from bottom to top all around) and then outsulation. I’d then include a ventilated drainage space and use a lath to use thin brick. But for the insulation type I’d like to consider rockwool instead of rigid foam, because of insect control and because I do worry about long-term foam shrinkage.
Lstiburek’s “perfect wall” in Building Science Corp. does list rockwool as an option in this strategy.
But what happens in the summer? Wouldn’t the solar drive cause water vapor to go through the rockwool and condense against the Grace Ice&Shield? Since rockwool repels water, does that mean I’d get drops of water held against the wall? Or would it allow for any condensate to run down safely the walls behind the rockwool to the flashings at the bottom?
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