I did an inspection this morning and ran across a roof valley that didn’t look quite right; it looks like the overlap is on the uphill side of the shingle rather than on the downhill side. My concern is that as water is flowing down the valley, it will flow under the shingle rather than on top of it. I may be looking at it incorrectly. But, I thought I’d post the images and see what all you fine folks have to say about it.
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And before everyone starts lighting me up for not posting the images, I’m still trying to figure out how to do that; I’ve only posted once before.
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Well I can not see what section of the roof is higher than the other or if that’s a dormer. The lower side of a roof needs to always go under, unless that’s side has a steeper pitch. If both sides meet at the ridge it really doesn’t matter, but usually the cut side or top side will be the larger of the roofs.
But also wind direction can also determine what side should go over, if you are in n a high wind area the cut side should be in the usual wind direction, that way high winds do not pick up the shingles and tear them off.
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Some manufacturer’s include this detail in the installation instructions, here’s one from GAF (Timberline):
There are three key points to this detail, the minimum 2" gap (looks about right in your photo), the clipping of the top corner (we called it the ‘dog ear’ in my roofing days) to direct water flow into the valley and sealing the valley shingles with mastic/roof cement.
Their metal valley graphic shows the dog ears a little bit better:
It was explained to me many years ago without cutting the dog ear water will hit the top point of the shingle and travel along the top edge (instead of down the valley) resulting in potential roof leaks.
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That’s a California valley, nothing to see here
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It appears the short side shingles where not cut long enough or cut at an angle. Water can flow under composition tabs.
Poorly installed California Cut Valley.
Refer to a licensed roofer for further evaluation and repairs where required.
Act upon any recommendtions therein.
Excellent information! Thank you to all that responded. It just didn’t look right so I noted it for further review. Thanks again!
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It’s called a california cut valley: Types of Valleys – InterNACHI Inspection Narrative Library