I’m building a new home with a metal shell. The exterior walls will be 2×4 wood studs. I will be using spray form insulation. Do I need a wrap or vapor barrier between the metal siding and wood studs?
Rickey
Tom: Let’s just stick with the question and I’m going to say, “No vapor barriers ever.” People confuse … There’s vapor barriers, there’s vapor retardants, and then there’s moisture barriers. What we use in Texas is a moisture barrier and it goes behind siding or brick to keep any of the wind-driven rain from getting to the structure. That’s the place it is used. Vapor barriers are never used in this climate. They’re used in northern climates on the inside behind the sheet rock, because when it gets freezing outside, the moisture wants to migrate from inside the house to outside. And when it gets to a point in the wall, it will start to freeze and cause a sheet of ice. So, that is where a true vapor barrier is used on the inside of homes in very cold climates.
Charlie: I know I may regret asking you this, but I’m going to anyway. You’re answering just the question. Is there more that you would say to Ricky?
Tom: The foam itself is a vapor barrier in many ways. Don’t use the foam at all, use the formaldehyde-free fiberglass. I think it’s a poor choice of insulation, but Charlie, we’re not talking about a building envelope on a wood-frame structure, we’re talking about a metal building. So, I didn’t want to get into that because he’s walking a fine line where I don’t think he’s going to have a lot of problem with it.
Charlie: Right.
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