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Exterior insulation to existing with stucco cladding?

viapapillon | Posted in GBA Pro Help on

Am I overcomplicating this assembly?

In Zone 5, we are adding new windows and exterior insulation to our 1930’s 2×4 1.5 story home.  Currently the walls are 2×4, cavity filled faced fiberglass batts and 3/4″ lap sheathing.

I thought I had it all figured out until the Stucco contractor threw me.  He wants to install stucco to 2 layers of felt on top of plywood. (with or without an air gap system).

Lets back up…On top of the existing sheathing I will be installing:
-Vaproshield SA WRB
-flash openings with liquid Vaproshield
-install thermal bucks to openings, setting directly into the wet vaproshield
-install cascadia clips and 3″ of mineral wool (Owens Corning thermafiber)
     (the cascadia clips are needed to support the weight of the 3 coat stucco)
metal furring strips attach to the Cascadia clips and the metal stucco lathe attached directly to those.  But the contractor wants “plywood”.  I can swap out the Z-girts (metal furring strips) and install “plywood”(or Densglass?), but now I am at a place where this entire assembly seems over-complicated, esp. if I need to incorporate an additional flashing detail into the 2 layers of felt into the thermal bucks.

We want stucco.  I did not want to use EPS/XPS because I want a higher perm rating.  Did this assembly become over complicated because I wanted stucco with the 3″ of mineral wool?  Should I scrap the thermal buck idea and use 2×4’s?  does this assembly seem good quality and instead of plywood use dens glass sheathing?

Any help is greatly appreciated.

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  1. derekisastro | | #1

    The 3 inches of exterior mineral wool seems like overkill to me and is over complicating your build.

    In zone 5 I believe you can get away with only need R-5 ... you can achieve that with a 1 inch layer of some foams, maybe needing 1.25 to 1.5 inches of mineral wool. That would make your assembly easier to work with.

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