Chimney flashing is a crucial component of your chimney for preventing water intrusion. IRC code 903.2.1 states that “Flashings shall be installed at wall and roof intersections, wherever there is a change in roof slope or direction and around roof openings. A flashing shall be installed to divert the water away from where the eave of a sloped roof intersects a vertical sidewall. Where flashing is of metal, the metal shall be corrosion resistant with a thickness of not less than 0.019 inch (0.5 mm) (No. 26 galvanized sheet)”. What exactly is it, though? We definitely will not be installing a strobe light on top of your chimney. Flashing is metal used to seal off openings in your home from water intrusion. There are two main components to the flashing around your chimney. First, you have step flashing. This is a series of small overlapping L-shaped pieces of metal placed underneath each course of shingles. The piece of metal is nailed on top of an extended portion of each course of shingles above the strip of shingles you see in each row. The next course of shingles then covers this piece of metal, and the process continues along the whole length of the chimney. Next, is the piece you see. A large piece of metal called the counter flashing is placed over the step flashing on the side of the chimney. Finally, the edges of this counter flashing are sealed with a roofing sealant.