R-Values. Exponential going the wrong direction. After R-15 or so you slip into the long tail. Good article here- http://www.energyvanguard.com/blog-buildin

R-Values. Exponential going the wrong direction. After R-15 or so you slip into the long tail. Good article here- http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/76941/The-Diminishing-Returns-of-Adding-More-Insulation http://www.energyvanguard.com/blog-building-science-HERS-BPI... PH is performance based, but the religion is a bit excessive on R. I do greatly value the air tightness and the quantitative approach. High R-Value walls are tough to build and get expensive quick. Double wall, exterior sheathing, more parts, more fasteners, etc. We use SIPS walls/roof that have very good R, very little thermal bridging and outstanding air tightness while being fast to build.