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Where is This Water Coming From?

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

Posted on Apr 13 2013 by Scott Gibson

Writing from Climate Zone 6, GBAGreenBuildingAdvisor.com 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 insulationInsulation, usually of fiberglass or mineral wool and often faced with paper, typically installed between studs in walls and between joists in ceiling cavities. Correct installation is crucial to performance. " consisting of 4 to 6 inches of closed-cell polyurethane spray foam plus unspecified cavity insulation, taped Zip System sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. , 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.

Yes, the photos are 'disturbing'

Eric Habegger suspects there are leaks in the standing seams, although he cautions it may be too early to jump to that conclusion. Possible, but not a sure bet.

"What jumped out at me though is the icicles in the interior," he adds. "That would seem to indicate that cold air is bypassing the insulation somewhere. That needs to be investigated. It perhaps is a simple, though not easy to fix, problem of air infiltration past the spray foam insulation where a gap or pulling away has occurred.

"That might allow warm moist air from the interior to cool and condense on the metal roof and then drip down," Habegger continues. "Just a possibility that needs to be investigated before jumping to a conclusion."

Yes, condensation is a possible explanation, says GBA senior editor Martin Holladay. "You need to pay attention to when the leak occurs," Holladay writes. "If the drips happen on warm days, with ice still on the roof, it's probably condensation. If the leaks happen when it's raining, you probably have a leaky roof."

It's also worth noting that Holladay's article on ice dam prevention advises, "Although so-called hot roofs (roofs without any ventilation) can work well, ice dams can still form on a hot roof if the snow is deep enough. (Very deep snow acts like insulation. If your roof is covered with two feet of fluffy snow, the bottom of the snowpack is insulated from cold outdoor temperatures. That raises the chance that melting will occur.) So, if your climate is very snowy, you probably want to stick with a cold (ventilated) roof."

Keith Gustafson has a shingled roof with a 3-in-12 pitch and he, too, has seen drips of water behind the soffit when the ice and snow are thick enough on his roof.

"Sometimes, things just are," he says. "The only totally watertight solution would be rubber [roofing]. No sloped roof system is designed to beat ice dams... I would consider several lengths of heat cable to be turned on the three days a year they are required."

Don't use standing-seam on low-slope roofs

No standing-seam roof will prove truly waterproof, writes GBA reader Hobbit. When enough depth, water will go sideways and find its way into the inevitable gaps between panels.

"This is why they're not recommended for low pitch," he says. "My 4 1/2-in-12 shed dormer is probably close to the limit of what [standing seam] can practically handle."

In his case, Hobbit didn't notice ice dams but he did assume that some of the melting snow and ice found its way past the roofing and made its way down over the peel-and-stick membrane, "hopefully all safely reaching the edge of the decking and dropping off under the drip edge."

No evidence inside of any problems inside, he adds, "other than the rafters bending under load."

Wait for next year to find out

Metzger is certain that the house is tight enough to prevent warm air from trickling up through the roof and condensing on the underside of the Galvalume. But the 3-foot overhang is uninsulated, and it was dripping with water on the first warm day of the year when snow on the roof was melting.

"I suppose it's possible it was massive condensation from the ice on the roof hitting the warm, humid outdoor air in the soffit," he says. "I would jump for joy if the answer was that simple! Though I might have to wait until next winter to find out. I'll need to remove a section of the tongue-and-groove soffit so I can witness the phenomenon."

The closed-cell foam sprayed on the inside of the roof sheathing is waterproof, Metzger says, so it could be a long time before evidence of a leak starts to show itself.

"I may never know if I had a leak inside until down the road, the OSB would start bulging up my metal roof," he adds. "A scenario I'd sometimes think about late at night."

Is the roofer responsible?

Another issue is whether the contractor who installed the roof is in some way responsible for the problems Metzger is now seeing. "He says he's never heard of this happening before," Metzger writes.

"If a new roof is leaking, the roofer is of course responsible," Holladay replies.

But the roofer is taking no responsibility," Metzger says, adding, "And as years go by any recourse I have diminishes. Taking him to court is the last thing I feel like doing. Lesson One when hiring a roofing contractor is go with reputation, not with price. The $3,000 I saved on the installation doesn't seem like much now that I have been having problems."

The mysterious drip he's now seeing is not the first sign of troubles. Last year, another "banner snowfall winter," the accumulated weight of snow on the roof pulled a 30-foot long panel down 6 inches, he says, "unbent the crimps and all."

The roofer wasn't willing to fix that problem, so Metzger had to set up staging and fix it himself.

"This winter I was half-way expecting the entire roof to catastrophically slide off the sheathing," he adds. "I mean, seriously, has anyone tested fastener systems for metal roofs on 1/2-inch Zip OSB sheathing? It can't be very strong... And 24 inches of accumulated snow is."

Another house Metzger built had asphalt shingles — one-third the price and "headache-free."

Our expert's opinion

Here what GBA technical director Peter Yost had to say:

David Metzger has several questions built into his situation and he and I had a pretty extensive email exchange on this building (which by the way, is a ).

To start, know that his building is pretty darn airtight, even in the cathedral ceiling/unvented roof assembly. Often, the 2x6 tongue-and-groove cathedral ceiling is part of a structural roof deck that spans from interior to exterior at the gable and eave overhangs — and so is often very tough to air seal — but that is not the case with Metger’s building.

Where is the water coming from?
Given when and under what conditions Metzger’s building has shown water leakage, my best assessment is that his well-insulated and air-sealed unvented roof has about R-24 or more on TOP of his roof cladding when it has 2-plus feet of snow up there for an extended period of time. There is enough heat loss trapped by the snow cover to result in melting over the portion of the roof above conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. but then it runs down and hits the 3-foot overhang that is quite cold and an ice dam develops. At a 3.5:12 pitch, the ice dam easily builds up enough water to overwhelm the 1-inch standing seam.

What is the minimum roof pitch for standing seam metal?
I checked in with my expert roofing contact at our local company. International Building Code states the minimum pitch for metal panels is 2.5:12 unless seams are soldered. Jancewicz & Son's approach is for anything less than 5:12, they typically spec high temp, full coverage ice and water shield with a fully sealed seam (during install), commercial grade sealants inside a double lock, and a vented roof.

Would pulling snow off just the overhang (and maybe then some) solve the problem?
Good question. Perhaps not, since the melt water is likely to still freeze at the overhang and create the dam, just more visibly without the snow cover.

Is the roofer the problem?
I think, ultimately, yes. You often get what you pay for, and this company just put on the cladding, rather than working through the potential issues this particular building presented for the cladding used.

So, what to do?
I hate to be mealy-mouthed about this but I am going to suggest two possibilities. One is to do nothing and see what happens next year and cross the bridge of a really unusually prolonged cold and snowy season if and when it presents itself. The other option is to go back to a professional-grade roofing contractor and get his or her recommendations.

Here is what Jancewicz suggests: Sorry to say, but start over. Twenty-four-gauge standing seam metal is essential for Climate Zone 6, as well as venting the assembly (see 2b above). Jancewicz is just about never the lowest bid on any project and they spend a lot of time training their sales staff to clearly explain the Jancewicz quality and value proposition.


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  1. David Metzger

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