Help sorting through metal roof assemblies.
I’m in CZ4 with a traditional attic (cellulose above ceiling drywall), and I’m trying to weigh a few metal roof options. Roof will be 24 gauge, standing seam with no striations, around 12”-16” per panel. The more I read on these forums and other sites, the more I talk myself in circles. I’m curious what others would do in my shoes. My considerations are longevity, performance and oil canning.
Option 1: Synthetic peel and stick with metal on top. Ventilation through attic at soffits and out ridge.
Option 2: Same as Option 1, but with 3/8 backer rod under each panel to reduce oil canning? Does this actually work?
Option 3: Same as Option 1/2, but with added ventilation above the roof deck. With drying through the attic, this is not necessary for drying — it would just be for performance / longevity. My architect is in favor of the thermal performance. Various products promote this, as do companies / builders online. I’ve also read speculation of longer life. Might come down to just a cost issue. With this route, there are 3 options:
– Mesh underneath the metal. Not enough airflow.
– Dimple mat. More gap than mesh, but still too small. Also gives backing to the panels, which may help oil canning? Can be used in a system with radiant barrier like Sharkskin.
– Notched underside wood battens. 3/4” to 1.5” gap. Wonder if the spacing of the battens affects oil canning at all?
In all cases, vent through eaves and out ridge. Roof slope must be high enough.
Option 4: It looks like some places promote just above deck ventilation. With a synthetic underlayment, I’m not sure how the sheathing would dry in this situation. In a poor design situation (i.e: no overhangs), would this be enough. What about with gable venting thrown in?
Thanks for any thoughts!
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