Wall section with stucco exterior cladding
My plan is to use Huber/Advantech Zip R sheathing with 1 and 1/2 inch rigid foam (2 inch total) with 2×6 on 16 inch centers. Then attach Delta dry and Stucco lath, then three course stucco.
1. How is the best way to attach the Dorken Delta material to the Zip R sheathing? (Fasteners?,into Studs?, how much penetration into stud)
2. My Architect is concerned with the weight of the Stucco on the structure, especially since the lath will be attached thru the 2 inch Zip then into studs. His concern is the cantilever or extended stucco layer so far from the 2×6 studs the stucco will have significant cracks due to the weight of stucco over time.
Your expert help is greatly appreciated.
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First, the basics. For 3-coat stucco, you need protection equivalent to 2 layers of 60 minute Grade D building paper. Grade D paper is mostly popular on the west coast, but is available everywhere. Most building inspectors will allow two layers of pretty much any type of WRB wrap. Some types of sheathing (Zip) have a WRB built into the surface, and if they are properly tapes and flashed, the sheathing itself an act as one of the layers. I don't think that Advantech is qualified as a WRB sheathing, so you would still need 2. I'm not familiar with Advantech R sheathing. Are you using Zip-R sheathing, or Advantech with a separate layer of 1-1/2" foam? Some types of foam also have a facing that can be taped and treated as a WRB for one of your layers.
Delta Dry is an impermeable dimpled membrane, so it will stop vapor driven from either side. It is intended to be installed outside a vapor permeable WRB. The idea is that vapor driven from either side will stop at the delta dry. Depending on conditions, any vapor that condenses will be able to drain to the bottom of the wall. Because it is the outer layer, it does not have to be taped and treated as a waterproof layer. You want to fasten the inner WRB and the Delta as little as possible. The fasteners for the stucco lath will hold everything in place. If the lath is going on quickly, just tack the WRB's in place with a few staples. Some WRBs require cap staples. I don't think the Delta does. Follow the instructions. Fasteners for the stucco lath should penetrate the studs by at least 1-1/2". This will be a bit of a challenge through the foam, but it is important. I wouldn't worry about the weight of the stucco. Stucco is installed successfully over foam all the time on wood construction.