How to insulate including vapor barrier in building with metal siding
I am planning on building a home in zone 3A (Dallas) by first erecting a metal building and then framing the inside. Plan is to use R-panel for outside and then 2×4 walls. What is the best way to insulate this including what type and location of vapor barrier
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I'm not sure what an R-panel is, but I think you are referring to a brand of steel roofing manufactured by McElroy Metal; this roofing panel can also be used as siding. It does not include any insulation.
There are several problems that arise when you try to insulate a steel-framed building. First of all, you need an air barrier. Second, you need a thermal envelope that is entirely outside of the steel framing or entirely inside of the steel framing.
Which approach do you intend to take?