Overclad EPS foam on top of stucco-covered fiberboard?
I'm doing a deep energy retrofit of my New Mexico house (zone 5B) and it's time to plan out the walls. The existing exterior walls have stucco cladding with no deliberate drainage gap, over two layers of tar paper, over fiberboard. In my extremely dry climate, this wall seems to have proven robust in its 42 years of life so far, as I have found no evidence of moisture damage whenever I have ripped out drywall or chiseled away stucco.
Given the cost-prohibitive nature of removing all the stucco, I am considering overcladding the wall with 4 few inches of high-density, termite-treated EPS foam and cladding it with a new layer of stucco or an EIFS-like polymeric equivalent. My thinking is that I would re-use the tar paper as the wall's drainage plane and keep the windows and doors in line with it, essentially putting them in the middle of the final wall assembly.
Ih there anything obviously wrong with this idea? One possible issue that comes to mind is the possibility of sandwiching the existing stucco between two vapor barriers (tar paper and foam). EPS is not really that much of a vapor barrier, but 4 inches of it may be enough to function as one. But the material between them would be cementitious, and the 8 annual inches of rain in this climate sort of restrict the damage you can do with less-than-perfect water-management, as my current stucco-over-fiberboard wall illustrates! Thoughts?
Posted Sun, 06/15/2014 - 19:00
Edited Mon, 06/16/2014 - 00:47
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