I am building a superinsulated, tight house in Los Angeles (temperatures frequently exceed 105 in summer). I am using spray-in closed cell foam in 2x6" stud wall, and would like to use 1" of polyiso foil-faced insulation outside the assembly with regular 3-layer stucco on top of that. Two questions that I would appreciate help with please: 1. From a structural perspective, nailing the stucco lathe outside the foam board -- is weight an issue here? The nails would need to be an 1" longer than my stucco sub normally uses and he is concerned that the weight would bend the nails and pull them through the foam causing failure.
2. From a building science perspective, there's a link to a building science piece on another discussion(http://www.buildingscience.com/documents/insights/bsi-001-the-perfect-wall) that has the house wrap between the plywood sheathing and the foam -- is this the right place for it? I would have thought outside the foam would work better. Thanks!
Posts: 5 | Location: Los Angeles | Registered: 19 June 2008
Have you gathered more information on your stucco over foam application? I'm looking at a similar system for new construction in Austin, but concerned about compromising the stucco installation. I've considered installing interior horizontal 2 inch thick furring on a 2x4 wall, with cellulose insulation. The furring provides additional cavity thickness, plus a thermal break.
Hi Bill, Unfortunately, nothing new on the foam/stucco. I'm afraid, I'm not following what you're planning with the horizontal furring. Furring will not provide a thermal break. Wood does not provide much R-value. If you are planning on an air space providing the thermal break, be aware that insulation needs to be in contact with your drywall to avoid heat transfer through convective looping.
Posts: 5 | Location: Los Angeles | Registered: 19 June 2008
2" deep horizontal furring would provide an additional 2" of cavity depth plus a 2" cavity over the studs for cellulose or batt insulation. Where the furring overlaps the studs there would not be a thermal break, nor at furred-out windows, however ~ 90% of the stud/plate/header area would be insulated.
Originally posted by buildgreen: Hi Bill, Unfortunately, nothing new on the foam/stucco. I'm afraid, I'm not following what you're planning with the horizontal furring. Furring will not provide a thermal break. Wood does not provide much R-value. If you are planning on an air space providing the thermal break, be aware that insulation needs to be in contact with your drywall to avoid heat transfer through convective looping.
If your planning to use a exterior stucco system, Regardless of what type, Three coat, once coat, EIFS etc. Do not use a foil face EPS board. The wall sytem needs to breath. A metal lath system over EPS board is not suggested. The lath needs to be secured directly to the structure in order for it to be properly supported. The EPS board is not a structural member therfor it cannot support the lath or cement weight. Which will get quite heavy. Also using a lath system requires expansion joints as well as control joints at every window, door and or opening in the wall. This may be ok in a commercial building, but on a home its ugly. My suggestion is to install a drainage EIFS system on the wall. Review the details carefully from the manufacture of the wall system used to assure that its being installed correctly. Uncorrect install is the primary reason for all the issues with EIFS systems. I suggest you go to the EDI web site.http://www.exterior-design-inst.com/ And get a qualified inspector to assit you with the install process. Also be aware that having an EIFS home may effect your insurance on the house. In our area NJ and many areas on the east coast, mortage companies and insurance companies and having issues with a EIFS home. Do to the law suites involving this type of product.
AS an inspector of this product, I have seen a shift over to the hard coat stucco systems like the one your thinking of using. Which is fine. But remember that this type of system your thinking of using requires all of the details the EIFS system requires and some more as well. Having someone assist you with proper install is the only way to assure yourself that its being installed correctly. Hope somewhere in this post I answered your question.
Posts: 865 | Location: New Jersey | Registered: 31 January 2006
