Metal roofing/insulation on a mountain home

Michael Shocklee
Next spring, after the snow melts, I am going to build my new home. It will be at 9,000 and has a 100lb/sq' snow load. The roof is a simple saltbox design. The second floor is an open loft with no attic. I am going to build this as green as my pocketbook will allow with as much insulation as I can and as sealed up as I can get it (with an HRV system). My question has to do with adding insulation above the plywood sheeting. I keep hearing to never, ever do this, that it will not add to the R factor and that it will induce many problems with ventilation and ice damming. But, I see people doing this all the time with 2x4 spacers and foam insulation boards. It would be great to seal up the roof with spray foam then 8" batting underneath the sheeting then a few extra inches above, before the metal.
Todd Miller
Isaiah Industries, Inc.
Thank you. Because your home is built without a traditional attic (and subsequent insulation), I do not see any problems with what you are proposing. I would stress ... make sure that the manufacturer of your metal roof approves of this sort of application. I assume you will in this case be running the 2x4 spacers horizontal, for fastening the metal roof.
Eric Novotny
An informed customer is the Best Customer!
I am not sure who is saying that insulation across the roof deck is bad. This is actually a great idea when done properly.

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