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Q&A Spotlight

Where is This Water Coming From?

A homeowner with a standing-seam metal roof wonders why water drips from the soffit

Is that drip something to worry about? A GBA reader from Climate Zone 6 is concerned about water that drips from the underside of his roof soffit when winter snow and ice begin to melt.
Image Credit: David Metzger

Writing from Climate Zone 6, GBA reader David Metzger is looking for some advice about his standing-seam metal roof. More to the point, why is there water dripping from the soffit when the winter’s accumulation of snow and ice starts to melt?

The shed roof showing evidence of problems has a pitch of 3 1/4-in-12 and is framed with I-joists. Metzger provides these additional details: “flash-and-batt insulation” consisting of 4 to 6 inches of closed-cell polyurethane spray foam plus unspecified cavity insulation, taped Zip System sheathing, followed by roofing underlayment. The Galvalume metal roofing has single-lock standing seams that are 1 inch high.

“Lots of snow build-up over winter,” he writes. “Due to the pitch and the amount of insulation, there are no conditions where snow slides off on its own. Eventually, ice builds up over top of the seam. As weather gets warmer, water is observed dripping out underneath of overhang (soffit) on low part of the roof.

“My guess is the entire roof is leaking at the standing seams and water is sheeting down roof plane, over the underlayment.”

Metzger asks whether a double-lock seam would fix the problem, but adds that if it doesn’t he’s really stuck because he won’t be able to take the metal sections apart and find another solution.

“Having done some research recently I’ve discovered that a 2- to 3-inch tall standing seam with a butyl sealant at every seam would have prevented this from happening,” he adds. “But it’s too late for that. As it is now, if I can probably take apart the roof — one 30-foot section at a time — cover the Zip sheathing with a waterproof underlayment, then re-bend each seam with sealant and a double-lock.”

What should he do? That’s the topic for this Q&A Spotlight.

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