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Asphalt Shingles in Open Valley


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I'm not aware of any shingle manufacturer that prohibit open valleys but there's things far more seriously wrong with the roof on that photo than the fact that it has an open valley.

The valley is lined with laminated shingles, shingles that are not intended for such low slopes, nor even for curved surfaces.  Even without an establishing shot, I'd say that roof has a serious framing error. The central area within that photo would have been better framed with a flat roof and a single membrane roofing material, such as Mod-bit, EPDM or TPO.

Until it's corrected, that area of the roof will always be a problem. Problems that are built into a house are among the most difficult and expensive to correct.

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There were many issues with this roof, the lining of the this valley being one of them. My understanding was that an open valley needs to be lined with flashing or a membrane, and that asphalt shingles are never acceptable, regardless of slope. I was curious if there were exceptions to this. Interestingly, this roof had several different valleys, all installed in different flavors of incorrect.


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When in doubt, imagine that trough full of snow, ice and then some rain.

The so-called builder has skewed the valley sideways to get some slope on it, maybe?

The roof on the left shows a reverse slope, and the needles usually collect at a low spot or a drain. I don't believe that work was ever approved by an authority.

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