Applying Stucco to Rigid Foam over CMUs
I am planning on exposing my earth-bermed house on the west side. We live in Ithaca, NY. Zone 5, sometimes 6. Unfortunately, the house was built 30 yrs ago as a rectangle, North to South. The short side is facing South. We only have windows on our short south side, so we are exposing the CMU blocks on the west to introduce some windows.
I am going to add 3″ of rigid foam over the vapor barrier that will go over the CMUs. Then, 2 layers of building paper, the lath, then stucco.
MY QUESTION IS: how do I attach all of the layers? Do I glue the vapor barrier, insulation and paper; Then mechanically fasten the lath and everything under it using 5″ tapcon screws? Or is there a better method using a plywood layer that I can staple the paper and lath to?
I am doing my West & South sides of my 72′ X 26″ single story home.
Thanks!
-Rick
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Replies
Rick,
I have never done this, so I would be happy to defer to the advice provided by someone who has. But here's how I would do it:
1. Attach the rigid foam with just enough adhesive to get it to stay in place.
2. Attach 1x4 vertical furring strips, 16 inches on center, with 5-inch Tapcons into the CMUs.
3. Attach paper-backed metal lath to the furring strips.
This isn't the only way to do it, for sure -- and it could be argued that you don't need the rainscreen gap, because the CMUs won't rot like a wood-framed wall would.
More information here: To Install Stucco Right, Include an Air Gap.
Thanks Martin, this seems like a great approach that I wll probably use.
Rick
Rick,
You application seems much better suited to an EIFS application (Exterior Insulation Finish System). You apply a drainage layer over the CMU (Drainwrap or Stucco Wrap), then EPS foam is installed on top and fastened mechanically with windlock windevil masonry screws (chemically/glue fastened systems are also available). The EPS is rasped (sanded) and a thin layer of polymer modified cementitious base coat is applied then a finsh coat that has various options in terms of style and colour. There's loads on the internet about this type of system. It is used extensively up here in Canada.