Roof foam – 2 or 4 layers?
I’m insulating the exterior of a gambrel barn. The roof needs 8″ of XPS insulation, and I’m wondering if two layers of 4″ foam will sufficiently block airflow to the roof deck, or if I would be better off doing four layers of 2″ foam. I’m doing this myself, so 2 layers will be easier to handle, I think
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