Stucco over exterior rigid foam – yea or nay?
I already posted this question under the title “accidental deep energy retrofit” but am hoping a stray stucco professional or engineer might weigh in with a more specific question in the title.
Proposed wall assembly: 2×4 framing (furred to 2×6 on the inside with polyiso foam and 1x, because we didn’t know this siding project was in our future), plywood sheathing, 1.5″ polyiso foam boards (taped) with the windows furred out on 2x2s, tar paper, lathe nailed to studs through foam with spacers, stucco.
Climate: high desert, annual rainfall averages 4″, 50+ year old stucco we are replacing was over tar paper only, with no signs of water damage. (This is to justify that we aren’t planning to include a rainscreen gap, though if you tell me the stucco will be sturdier with furring strips, OK)
Concerns: Contractor, and the stucco rep he talked to, say the most they can do is western 1 coat over 1″ of foam. They are concerned about the weight 3 coat stucco hanging 1.5″ away from the studs. They were visualizing lathe staples. Contractor is open to trying nails, if I am confident.
So, should I be confident?
I don’t want to use 1-coat (or EIFS) because, as my contractor will admit, it’s not that hard to put a hole in it. All the exterior foam retrofits I can find documentation on use other kinds of siding. If necessary, we can use hardie siding or plywood, but for aesthetic reasons I prefer stucco (we are accenting other parts of the house with corrugated metal and reclaimed redwood b&b).
Experience? Pictures? Links? Thanks.