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.
We built our timberframe home with sip panels 7 years ago. The roof has sip panels. Not long after building we noticed our downspouts filled with granular crystals from the roof and the shingles were curling. We put the roof right on top of the panels with ice guard underneath. At home shows we started questioning roofers about our situation. We bit the bullet and installed a metal roof last year. When they were tearing off the shingles they saw evidence of the start of dry rot on our sip panels. They took pictures and showed us. We put in a cold roof system under the metal roof. If you have a sip roof or are putting one on, please research, research, research before applying the shingles directly on top of the sip panels with no venilation. Our metal roofer told us we were third homeowners with sip panel roof to contact him with this problem. One homeowners roof was 12 years old and in quite serious shape. Most sip panel manufacturers dance around this question of venting or not to vent. Please check this out throughly so you don’t end up replacing a roof only 7 years old like we had to do to head off serious problems down the road.
Comment by Karen — September 25, 2010 @ 8:44 am
what is a cold roof system? We are going to put a steel roof over our SIP roof panels but I don’t know what a cold roof is.
Comment by Ruby Mayes — May 17, 2012 @ 1:31 pm
A cold roof is when a chamber is built to create a roof above / on top of the existing roof. The resulting chamber is vented with fresh air intakes at the bottom and exhaust at the ridge. Typically it ill have a depth of 2 – 4″.
Comment by toddmiller — May 17, 2012 @ 1:44 pm