Replies

1. GBA Editor
   Martin Holladay | Oct 31, 2016 06:24am | #1

   Richard,
   There is no single answer to your question. Your climate is relatively mild, so there is less of a pressing need in your climate for wall insulation than in a climate like Minnesota's.

   Brick veneer homes often have problems with inward solar vapor drive, so I'm a strong believer in the use of continuous rigid foam on the exterior side of the OSB sheathing for any house with brick veneer. In your climate, there are no limitations on foam thickness. Even 1 inch of rigid foam will improve the thermal performance of your wall and reduce the chance of moisture damage to the OSB.

   Here are links to two relevant articles:

   How to Install Rigid Foam Sheathing

   Flashing Brick Veneer

2. 
   Dana1 | Oct 31, 2016 08:55am | #2

   It takes at least an inch of foam sheathing on a 2x4 wall to hit IRC 2015 code minimum performance for zone 3.

   http://codes.iccsafe.org/app/book/content/2015-I-Codes/2015%20IRC%20HTML/Chapter%2011.html

   And inch of foil-faced polyiso is easier for the uninitiated to air seal, and with shiny foil facing the cavity it would offer another ~R1 of average performance.

   If fiber insulation is used, air seal the framing to the sheathing inside every stud bay, and if batts, take the time to fit them as perfectly as possible, with no gaps or voids. (Damp sprayed cellulose or damp sprayed fiberglass would have an inherently good fit.) If foam, open cell foam offers the best value, and higher drying rates toward the interior. Even 1" of 2lb closed cell uses more polymer than 3.5" of half-pound open cell foam, and even a full-fill of closed cell only adds about R1 to the whole-wall performance (after accounting for the thermal bridging), despite a dramatically higher center-cavity R. That R1 can be recovered far more cheaply by adding another 1/4" to the foam sheathing thickness (or 1/4" XPS siding underlayment on the interior side, under the wallboard.)

3. 
   user-2310254 | Oct 31, 2016 09:20am | #3

   Alabama follows the 2009 International Residential Code, although municipalities can adopt stricter requirements. Having to follow any code may be a culture shock for some builders since they were free to do whatever they wanted until 2012. Adding foam isn't difficult, but it will likely be an additional cost. A product that combines sheathing with foam (like Thermasheath) would probably go up more quickly. If you are building a custom home, it will be easier to deviate from local standard practices.

4. Expert Member
   Dana Dorsett | Oct 31, 2016 01:23pm | #4

   If you're having to educate the builder &/or crews, the learning curve would be shorter using something like OX SIS or 1.5" ZIP-R rather than OSB + foam separately. That would be trading a higher material cost for lower labor costs and lower installation time. With ZIP-R you also save the cost/time of housewrap, since it has a factory applied weather resistant barrier, and is fine as long as you follow the taping protocol for weather-sealing the seams.

   http://www.huberwood.com/zipsystem/products/zip-system-rsheathing

   A difference between OX SIS & ZIP-R is that ZIP has 1/2" OSB is on the exterior side of the foam, which makes the brick-tie installation nearly identical to what old-schoolers are accustomed to. With SIS you may have to through-screw the ties to the studs, since the SIS itself is very flexible compared to OSB, and the structural layer is pretty thin, which may make for lower fastener retention.