Tips on Applying Masonry Stone over EPS Foam
I am building a new home in Park City Utah at 7500’ which is a Climate Zone 6. The climate is relative dry as the average humidity is about 43% for the year.
I hired Heliocentric from SLC to work with my Architect to help maximize the efficiency of my new home which included 3D modeling overlaid with climate analysis and site solar survey. The result was a 35 page report detailing recommendations that are not only foreign but intimating to all the GC’s and sub contractors in the area. Consequently, I am forced to research the application of the recommendations myself.
My questions today are:
The recommendations were to use EPS foam on the exterior walls. Based upon cost and aesthetic factors I have chosen 2” EPS glued to a sealed OSB, blown fiberglass over 2”x6” 16”OC.
The Masons I have interviewed are not comfortable installing a dry stacked stone over the foam. 1) I am looking for recommendations on the best method to apply the dry stacked stone over the 2” EPS 2) should a vapor barrier be used as the code calls for two layers of 30lb felt? 3) Will there be any issues in the event there is foam shrinkage? 4) Any special sealing issues to be aware of? 5)Other factors to be concerned with?
The upper portion of the home will be Stucco? My Sutcco contractor sees no issues. 10 Are there any? 2) Using EIFS will provide additional R values but there have been very negative reviews of this product. Opinions?
Thank you for your help.
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Replies
Dennis,
I'm not sure what you mean by dry stacked stone. I know what dry stacked stone is for garden walls or a stone fence -- but not when you are talking about siding. Presumably your masons have a method of integrating their siding with the wall by including masonry ties.
The basic trick for installing stucco or stone siding on the exterior wall with foam sheathing is to first install vertical 1x4 furring strips over the foam. The furring strips are screwed through the foam into the studs. Once you have the furring strips, you can proceed using one of several approaches.
Here is a useful NAHB document that shows several ways to include a rainscreen in a wall with stone siding:
http://www.benjaminobdyke.com/resources/251/NAHB_Rainscreen_Report_01.09.pdf
Dennis,
You mention 2" EPS and say your stucco contractor sees no issues, but then you suggest that EIFS would add R-value. Were you thinking to install traditional 3-coat cement stucco over 2" EPS? This would have no thermal disadvantage vs. EIFS.
Here's a very informative website by an experienced stucco contractor: http://www.rtbullard.com/
This is all old-school, "real" stucco, and RT Bullard repeatedly refers to "EIFS garbage" and describes how flimsy it is, and how many failures he's seen. There are examples on the site where he replaces failed EIFS with traditional stucco. Unfortunately he has no examples of traditional stucco installed over insulation.
If you install traditional stucco over furring strips, you can use a method similar to installing over bare studs. For example you could choose a rib lath capable of spanning the spacing between furring strips. See these links:
http://www.dehavenconstruction.com/stucco/open-frame-stucco.php
http://www.sfu.ca/~nicolea/books/Chapter04.htm
Thank you for your response, regarding using the furring strips, I assume we use the felt over the foam just as we would over OSB. I also assume between the furring strips wall drainage spacers can be used for the rain screen. (I haven't read the Rain Screen article yet)
Regarding Stucco, Thank you for you input as I have not read too much favorable about EIFS and I am searching if anyone has anything positive to say about it other than cost savings.
Dennis,
I'm a builder out here in SLC, and work a lot the Park City area. You have hired a very knowledgeable and competent Energy Engineer (Heliocentric is one of the best), now the trick is to find good builder to implement the engineer's design. Super insulation (double wall construction/exterior foam sheathing) and progressive homebuilding details are something we eat, sleep, and breathe.
It sounds like you've got a very exciting project-- I would love to hear more about it. We've got a couple homes up in Jeremy Ranch and the Silver Creek area in construction right now if you would like to see our work.
Feel free to contact me at brett at g-build dot com.