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Ventilated Metal Roof with an Unvented Attic

KingKray | Posted in Energy Efficiency and Durability on

Howdy! Currently building in Seattle and have concerns about roof sheathing rot in my roof assembly. I have an unvented attic insulation with closed cell foam spray. Above the insulation layer is 5/8” plywood, vapor permeable Mento 5000, 1/2” VentGrid, finished with standing seam metal roofing. The metal roof will have perforated channels at the eaves and ridge to allow for airflow.

For the interior I’ll need to mitigate moisture with a dehumidifier. For the exterior I’m concerned about ambient winter moisture or summer condensation within the roof ventilation system causing consistent moisture exposure for the sheathing given the WRB is vapor permeable. Any thoughts on whether this is a true concern or not? 

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