Cavallaro, a GBA reader from Arkansas, replaced a wood shingle roof on his 1975 A-frame house last year with standing-seam metal, but far from enjoying the upgrade Cavallaro is ready to tear off the new roof and start again.
The problem? Mold.
“The new vapor-impermeable roof caused moisture to build up inside,” he reports in this recent Q&A post. “In addition, the metal changed the temperature of the interior roofline causing condensation build up and mold to grow all along the interior roof during winter.”
The roof consists of 2-in.-thick tongue-and-groove boards—no attic, no air gap, and apparently no insulation. Just wood. Mold is one issue, odor is another. In the heat of summer, Cavallaro says, the metal roofing heats up the underlayment and makes a “horrendous” smell inside the house. All of it, he says, has been an emotional challenge.
Cavallaro has concluded that the metal roofing has to come off. He’d add 3 in. of polyiso insulation, OSB sheathing, a self-adhering waterproofing membrane, underlayment, and then, finally, reinstall the metal roofing.
“Is this the correct solution in addition to reducing interior moisture?” he asks. “Is an air gap necessary directly below the metal roof for efficiency gains? Will we smell the second layer of underlayment in the summer? How much more efficient is a light-colored roof than a darker (charcoal gray) roof?”
Those questions are where we start this Q&A Spotlight.
A roof guaranteed to fail
As built, writes Akos, the roof was bound to fail. The layer of Ice & Water Shield installed over the T&G roof is vapor impermeable, so winter condensation and mold should come as no surprise.
“The solution with exterior rigid insulation you are looking at…
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