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TO: Roofing companies FROM: Steve McBride, Douglas Building Official SUBJECT: Roofing Requirements for Valleys DATE: 7/6/20 The following is a clarification for closed valleys for asphalt shingle roofing in the City of Douglas. References are included to the 2018 International Residential Code (IRC). We also verified with three roofing manufacturers whose products are currently being used in Douglas. 1. Per IRC-Sec. R905.2.8.2, install directly to the roof sheathing, a valley liner of smooth roll roofing complying with ASTM D6380 and not less than 36 inches wide. Or, install directly to the roof sheathing, a valley liner of self-adhering polymer-modified bitumen underlayment (ice barrier – method preferred by City) complying with ASTM D1970. Make sure the valley liner is tight to the deck without bridging in the center of the valley. M E M O R A N D U M