What type of roofing material is best above a SIP roof with PV modules on top?
I am a home owner in the final design stage for a net-zero house. The house will be located in update New York near Albany at an elevation of 1360 feet and is probably closer to Zone 6 than Zone 5. The area can have heavy snowfalls and also ice storms.
The house will have SIP walls and an 8.25 inch R50 SIP roof. I plan to add 2 inches of polyiso insulation either to the outside or the inside of the SIP roof in order to increase the R-value to R62. The ceiling below the SIP roof will be a cathedral ceiling.
On top of the roof 44 PV modules and their racking system will be placed which will essentially cover the south facing portion of the roof except for the overhangs. This will tend to hold snow or ice on the roof.
The main question is what type of roofing material is best to use for this roof assembly and what would keep this rather unwieldy roof assembly with the PV modules on top structurally sound? I have considered either asphalt shingles or a standing seam metal roof. The metal roof seems better but it would also be twice as expensive.
Also should the roof be vented or can it be a non-vented roof? Is it possible that with a non-vented roof, the R50 SIP panel and an additional 2 inches of polyiso insulation added probably on top, that it would be enough insulation so ice damming would not be a problem as long as all air leaks in the roof area were sealed properly? Is there a way to add a drainage plane to a non-venting roof so that any water that does get under the roof or any condensation that occurs has a way to drain out?
If a vented roof is used, how deep should the vented space be? I have read that 2 inches is recommended or could it be less?
Also what would the roof assembly consist of? Where would vapor barriers or air barriers in addition to a waterproof underlayment be placed?
Related questions are does a metal roof prevent water from ice dams getting underneath the roof? Is it better to use the metal roof since the racking system for the PV modules can be attached to the seams of the metal roof without the multiple long penetrations down to blocking in the roof SIP panel that an asphalt shingle roof would require?
Also has anyone used a product called Cool-Vent which is a ventilated nail base polyiso insulation panel? The website for this product is at http://www.hunterpanels.com
As you can see I have a number of questions. Any help with the answers would be greatly appreciated.
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