In a region that’s half-cold half-warm, does it matter which side of insulation you put a vapor barrier?
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The vapor barrier goes on the warm side of the insulation, with warm side meaning the exterior if you’re in a hot climate and the interior if you’re in a cold climate. What if you’re in a climate that’s half-hot half-cold? Where the heating degree days and cooling degree days are equal, does it matter which side of insulation you put a vapor barrier?
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Eco,
In that situation, I would put it "In the middle" and design the wall to dry towards both sides of the VB. In zone 3/4, there are hot summers and cold winters, and high humidity, and low humidity. If I had to choose inside or outside, I'd put the vapor barrier on the outside, unless it's really cold during the cold part of the year. The humidity outside (in zone A at least) will nearly always be greater than the humidity inside, and you want to keep that out. The HVAC should be able to handle the conditions inside.
I like that: Where temperatures are [even], vapor barrier goes on the humid side.
Thanks
I think vapor barriers in that climate are a bad idea. If you must have something, a vapor retarder is a better idea. You are also in a warm enough climate that almost any amount of exterior rigid provides condensation control, at which point no vapor retarders are needed.
In the middle is always safe. And yes, it should be a Class 2 or 3 vapor retarder, not a Class 1 VB. If your outdoor temperatures don't vary from indoor by more than about 20F, then you don't need any VR at all. As the difference gets larger, you need to be a bit more careful about where and whether to add a VR.