![]() End laps shall be 4 inches and shall be offset by 6 feet. For roof slopes of four units vertical in 12 units horizontal (4:12) or greater, underlayment shall be one layer applied in the following manner: underlayment shall be applied shingle fashion, parallel to and starting from the eave and lapped 2 inches, Distortions in the underlayment shall not interfere with the ability of the shingles to seal. Distortions in the underlayment shall not interfere with the ability of the shingles to seal. Starting at the eave, apply 36-inch-wide sheets of underlayment, overlapping successive sheets 19 inches. TABLE R905.1.1(2) UNDERLAYMENT APPLICATION ROOF COVERINGįor roof slopes from two units vertical in 12 units horizontal (2:12), up to four units vertical in 12 units horizontal (4:12), underlayment shall be two layers applied in the following manner: apply a 19-inch strip of underlayment felt parallel to and starting at the eaves. MAXIMUM ULTIMATE DESIGN WIND SPEED, V ult ≥ 140 MPHĪSTM D226 Type I ASTM D4869 Type I, II, III or IV ASTM D6757ĪSTM D226 Type II ASTM D4869 Type IV ASTM D6757ĪSTM D226 Type II ASTM D2626 Type I ASTM D6380 Class M mineral- surfaced roll roofingĪSTM D226 Type I or II ASTM D4869 Type I, II, III or IVĪSTM D226 Type I ASTM D4869 Type I, II, III or IV MAXIMUM ULTIMATE DESIGN WIND SPEED, V ult < 140 MPH TABLE R905.1.1(1) UNDERLAYMENT TYPES ROOF COVERING ![]() An approved underlayment for the applicable roof covering for maximum ultimate design wind speeds, V ult, less than 140 miles per hour shall be applied over the entire roof over the 4-inch-wide (102 mm) membrane strips. As an alternative, a minimum 4-inch-wide (102 mm) strip of self-adhering polymer-modified bitumen membrane complying with ASTM D1970, installed in accordance with the manufacturer's instructions for the deck material, shall be applied over all joints in the roof decking.As an alternative, self-adhering polymer-modified bitumen underlayment complying with ASTM D1970 installed in accordance with both the underlayment manufacturer's and roof covering manufacturer's instructions for the deck material, roof ventilation configuration and climate exposure for the roof covering to be installed, shall be permitted.
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