Synthetic over Grace Ice & Water?

C P
8/11/2017
New construction in Southern Wisconsin. Typical gable style: living space, then drywall, vapor barrier, R38 batts, open attic, trusses, 5/8 plywood decking, rib steel panels. Good soffit and ridge vents. I put down two courses of Grace Ice & Water and will use synthetic for the rest of the roof. Do I need synthetic over the I&W to prevent it from sticking to the steel? The manufacturer does not require it, but I want to upgrade where appropriate. My other concern is condensation: Should I use fan-fold insulation over the Grace? What about the new three-dimensional mesh like "cedar breather" by Benjamin Obdyke? Unnecessary? Thanks!
Todd Miller
Classic Products, Inc.
8/11/2017
As long as the ice and watershield is a non-granulated product, you should not need the slip sheet over it ... there is no real harm in it but ultimately putting underlayment on top just means more holes in the system. I am not a huge fan of insulation on the roof top as it can cause issues with fasteners being over-driven. As long as your attic is properly vented and you have the vapor barrier behind your drywall, I do not think you will encounter any condensation issues, so no need for the mesh material. Here's an article on ventilation from one of our member manufacturers that may interest you: https://www.classicmetalroofingsystems.com/blog/ventilation/
Todd Miller
Classic Products, Inc.
8/11/2017
Because of having good ventilation, I see no downside to ice and watershield on the entire roof. However, assuming the roof has decent pitch and the roof is installed properly, I do not feel it is necessary. If it gives you extra peace of mind, though, it's not a bad upgrade as you say.

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