Moisture concerns with double stud in 4a?
First off, this is a great website! I have been reading all that I can on super-insulated homes and this site has been a huge help.
We are in the planning stages to build a new home (which we hope to be “THE” home that last the rest of our lifetime). We would like to be as efficient as possible with energy use, as well as from a construction cost standpoint. I am willing to pay extra for a system that will pay off down the road, but also don’t have an unlimited budget (who does?) so I have to be smart where we spend our money. I live in central KY, which is zone 4a, so I would like to build a “Pretty Good House” with R-30 walls and R-60 attic. I also want a brick exterior if that matters.
I have read about the pros and cons of double stud walls vs. traditional framing with rigid foam added to the exterior and have waffled back and forth as to what seems to be the best in my area. I have read that double stud seems to be a bit cheaper to build than rigid foam on the exterior, and is easier to install the exterior features like windows, doors and fixtures. However, I worry about moisture build-up. I know that zone 4a doesn’t have that much of a concern, but it also seems like opinions vary from person to person and year to year about whether some rigid foam is needed. It seems to be a unanimous opinion that rigid foam won’t hurt, and for Zone 4a, any thickness of foam is enough to control the moisture. However, those articles that I have found that say any thickness of foam board is acceptable for 4a are only talking about traditional framing techniques, and not double stud. I don’t think I have found an article the explicitly says that exterior foam insulation is not necessary for double stud in 4a.
So, to get right to it… For zone 4a, if I go with double stud wall construction, do I also need to install rigid foam board on the exterior? And, if I do, does that lessen the cost savings of going with double stud construction enough to the point where I might as well go traditional 2×4 or 2×6 with a couple of inches of exterior foam? It seems like going double stud PLUS rigid foam board on the exterior will be way more than the R values I am needing for my area, but I can’t figure out if that is still cheaper than going 2×4 or 2×6 with 4″ of exterior foam.
Any help would be greatly appreciated. (I also have a question about HVAC, but I’ll save that for another time).
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