Best Roof Insulation

This is an article written by a builder in the States.  He is describing probably the best roof insulation system.   Here in Ontario we have new insulation requirement in which the insulation described below wouldn't comply.  We would have to have more rigid insulation either on the inside or outside of the rafters. I have used this insulation system with rigid insulation bonded to OSB board.  In my designs, the roof was constructed of beams, either solid wood or glulams and then sheathed with 1 1/2 inch tongue and groove decking (exposed to the inside).  It is well known that vaulted ceilings are more efficient than dead space attics. Heated air becomes stratified and acts as insulation.  The Code recognizes this and allows lower insulation values to be built into the roof.

"Over the last year I've really been working on how to get my houses to the next level of greater energy efficiency and this video will show you my latest secret.  We're laying down a thick layer of rigid ISO foam boards on top of the roof .  We are using  1.5" of foam bonded to 1/2" OSB decking.  This will make a continuous blanket of R9.6 insulation on top of the roof plus the 5.5" of open cell spray foam inside on the underside of the roof for a total foam R value of R28.6.  I really like that this foam on the roof will span over our 2x6 roof rafters and eliminate thermal bridging at the wood rafters.  This turns our conventionally framed house into a sort of SIPS hybrid.  I also want to mention that our roof is a highly reflective silver "Galvalume" standing seam metal roof that acts as a radiant barrier.  I foresee very low cooling bills for this little farmhouse!  -Matt Risinge"