Flashing is required at all wall and roof intersections, wherever there is a change in roof slope or direction, and around roof openings. When flashing is metal, it must be corrosion resistant metal with a thickness of not less than 0.019 inch (No. 26 galvanized sheet). (R903.2.)
Valleys must be lined in accordance with the shingle manufacturers written instructions. In addition, valleys may be of any of the following:
For open valleys lined with metal, the valley lining must be at least 24 inches wide and of galvanized steel of at least 26 gauge or other approved materials.
For open valleys, two plies of roll roofing may be permitted. The bottom layer must be at least 18 inches wide and the top layer at least 36 inches wide.
For closed valleys (valleys covered with shingles), valley lining of one ply of smooth roll roofing complying with ASTM D 6380 Class S Type III, Class M Type II, or ASTM D 3909 and at least 36 inches wide or one of the two methods previously listed may be used.
Crickets or Saddles
Crickets or saddles are required on the ridge side of any chimney or penetration greater than 30 inches wide. Cricket or saddle coverings must be of sheet metal or of the same material as the roof covering.
Flashing against a vertical sidewall must be by the step-flashing method. Flashing against vertical front walls, soil stacks, vent pipes, and chimney flashing must be in accordance with the asphalt shingle manufacturer’s printed instructions.