Feasibility of exterior insulated stucco panels
In the process of trying to finalize the wall design that would allow 2.5″ exterior rigid “outsulation” over CDX sheathing. Planning for final stucco/stone veneer exterior. The issues that have been discussed on the board are surfacing. Two that concern me the most :
1. How to secure the weight of the stucco (not so much an issue with an EIFS) or the stone veneer with thickness that is typically 1.5-2″ thick, that far from the structural member of the wall. Use of long screws and fasteners are worrisome, their placement, possible failure or compromise over time concern me. Even with an engineering detail, it seems very counterintuitive to hang all that weight so far from the structural member of the wall . To this end, I happened to be watching a local commercial building go up not far from my work, they used Zip wall over stick framing. Then attached what appear to be metal insulated panels with concealed attachment points. Some Googling on the matter, I see they have some with stucco finishes, a baked-on sort of paint and aggregate that gives the feel and look of stucco. Of course you have the seams to deal with, but this lightweight, less labor intensive options seems interesting. May also be less costly? Anybody familiar with such an option? If they can be attached atop battens secured on top of the rigid insulation panel, may obviate the cost and labor of a weepage plane?
2. I see weepage planes are designed below the rigid insulation (closer to the wall) doesn’t this 1/4″ area that allows air to circulate totally undermine the insulation? I am thinking doesn’t the dew point require the insulation to be directly adherent to the exterior sheathing?
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Replies
Sal,
First of all, stucco and stone veneer are tricky cladding choices for wood-framed buildings, as you probably know. Traditionally, a stone building consists of a load-bearing (structural) wall. Traditionally, stucco is a finish for a masonry building. Adapting these traditional styles to wood-framed buildings is not only fake -- it often leads to moisture problems.
If you go forward with your plan, stucco will be easier to detail than stone veneer. For more information on stucco over wood-framed walls, see To Install Stucco Right, Include an Air Gap.
You wrote, "I see weepage planes are designed below the rigid insulation." Where do you see that?
If you install wrinkled or bumpy housewrap behind rigid foam (especially over OSB), the very small thermal penalty is often outweighed by the advantages the layer provides -- a reduction in moisture accumulation at that vulnerable layer. For more information on this issue, see Mind the Gap, Eh!
In that article, Lstiburek wrote, "What works? Grooved foam, “bumpy” OSB, “crinkled” building wrap, 1/8-inch polypropylene mesh, dimpled polypropylene sheets. Lots of stuff .... But won’t the tiny gap cause a loss of thermal performance of the foam sheathing? Yes. How much? About 5 percent of the thermal performance of the foam sheathing (not the entire wall assembly) with the 1/8-inch gap, less with a smaller gap. With “crinkly” stuff you loose next to nothing7 Is it worth it? Yes, in my opinion, the loss in thermal performance is trivial compared to the reduced risk and improved durability."