Closed-valley shingling options

Q: Do closed valleys make sense on roofs covered with asphalt shingles? We've had a successful roof of this kind for the last 15 years, applied after the leak-prone roof that was installed before with open valleys. Trouble is, we're getting lots of resistance from our new contractor. He claims closed valleys are not suitable because the build-up of ice and snow can drive freezing water under the shingles. Were we just lucky the last time?

A: The reluctance you're having with your contractor is quite typical, though his concerns are unfounded. Ask him this: If the roofs he installs with open, aluminum-covered valleys don't leak, how would lapping shingles on top of an already impervious surface cause leaking? The lapped shingles simply offer more protection to the already-protected valley, preventing heavy rains from being driven up underneath the aluminum as water cascades down one side of the valley and up the other. All valley surfaces are completely covered in the same shingles used on the rest of the roof. You might also mention to your contractor that lapped valleys take less time to install than open ones, since they involve less trimming. I suspect his reluctance is simply because the whole idea is new to him. Rest assured, as your experience has shown, lapped valleys work much better than open ones. They look better, too. As long as your new roof includes ice and water shield installed underneath all valleys and eaves, you'll be fine. Lapping valleys works best with shingles that have no tabular divisions. Non-laminated, architectural shingles are ideal.