According to Green Building Advisor’s Scott Gibson, vented rainscreens have become an increasingly common exterior detail for walls. Builders use the product to add an air space between the sheathing and the siding to help carry away moisture and prolong the life of the siding. Now, other construction professionals are wondering whether vented rainscreens will be valuable on roofs as well? See below for some insight.
James Morgan’s first question is whether the attic is ventilated, which would leave the underside of the roof sheathing open for inspection. If the attic is ventilated, Morgan says a rainscreen detail on the roof is unnecessary.
To Ron Keagle, the need for a rainscreen on a roof generally doesn’t seem clear. In this case, with spray foam on the underside of the roof deck with no ventilation intended, why not just lay the metal roofing directly on top of the sheathing?
“What would be the point of creating an air space between the top of the decking and the bottom of the metal roof?” he asks.
The point, replies Morgan, is that sooner or later the roof will leak, as all roofs eventually leak. “When the underside of the roof sheathing cannot be inspected,” he adds, “a free drainage plane immediately below the roof finish ensures the sheathing has good long-term protection from concealed moisture and rot.”
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