Metal valleys tend to clear themselves of debris better than woven or one-cut valleys. I never had a problem with expansion/contraction messing with the shingles in Michigan. It's more work during the installation for the roofers, all the cuts and such. Maybe this is why they're steering you towards the woven type? Whatever you end up with, see if you can make sure that the roofers cut off the "ears" properly. This is the point left at the top of the valley shingle when it is cut. This helps keep water from catching on the point and moving sideways, instead of down. Tom
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18 years ago