I'm designing a house with a cathedral ceiling with exposed structural beams, with structural decking above, and then rigid foam insulation above the decking. Per the 2012 Virginia Residential Code Table N1102.1.1 I know that I need to have R-38 roof insulation. Where do I find out how thick my rigid insulation needs to be to reach that R value?
2012 IRC and 2012 Virginia Residential Code
2012 IRC and 2012 Virginia Residential Code