I’m covering a closed-cut valley with laminated shingles, and the instructions say to extend the ends of the shingles at least 12 in. onto the adjoining roof. Where is the 12 in. measured from on the shingle? If I measure at the bottom edge, then only 8 in. of the top edge extends onto the adjoining roof.
—Patrick Crofts, Dublin, Calif.
Mike Guertin: Because of the angle of the valley in relation to the horizontal line of the shingles and square shingle ends, it isn’t obvious where you should measure the 12-in. point from. Is it the bottom corner, the top corner, or the nail line to the centerline of the valley? I checked the American Roofing Manufacturers Association’s Residential Asphalt Roofing Manual as well as the installation instructions from several shingle makers, but none specify in words or drawings where to measure from. I called two shingle manufacturers and stumped the customer-service representatives. The companies responded after checking with their technical people, and the answer in both cases was to measure the 12 in. at the top corner of the shingle. One company rep noted that the 12 in. along the top edge is a general target and doesn’t have to be perfect to satisfy the warranty.
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