Ask Todd Miller: Metal Roofing Expert

A homeowner asked me the following:
Todd, we are building a home with 8″ structural insulated panels (SIPS) for the roof decking (9/12) and want to use a Fabral SSR roof on top. As an engineer, I know the value of ventilation, but when asked, the roof & SIP manufacturers point at each other and say, ‘whatever he says’. Do I need to spend a fortune to build up a secondary decking system with lathe on top of the SIP for ventilation, or can I slap the metal directly on the SIP (with ice shield)?

My Answer:
Great question. In my experience, if you have a vapor barrier on the bottom side of the SIPs and if the joints between the SIPs are properly splined and sealed to prevent moisture migration, you should be fine.

There are, though, as an option, some SIP panels with built-in ventilation grooves. You could consider those as well.