Roof valleys – open metal or closed cut?
I want my roof to be as leak-proof and long-lasting as possible. Can’t afford standing seam metal, though, so it will be mid-grade architectural asphalt shingles installed with meticulous detail. I’m in a mixed humid climate zone 4A. Roof is 5:12 slope, with a couple of valleys. I’m trying to decide on the best way to do the valleys – open metal valleys, or closed cut ones.
The closed cut valleys are cheaper and commonly done in my area, but they tend to wear out sooner due to the high volume of water in the valley washing away the protective grit on the shingles there before on the rest of the roof.
I’m leaning towards an open metal valley, but I’ve had contractors disagree – saying that the metal expands and contracts too much. But I’ve also heard that, properly done, they are very effective and can last a long time.
I’ve been somewhat confused about the installation instructions for metal valleys. Most state to use clips on the long sides of the valleys to allow the metal to expand/contract as needed, and to not nail the metal in place. BUT the shingles seem to be nailed through the metal about 6″ outside the bottom of the valley, which contradicts the “no nailing through the metal”.
Any thoughts, experiences, or recommendations for roof valleys?
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