What is counter flashing?

Counter flashing is a metal component installed in the mortar joints of masonry or into the existing siding of a building, designed to overlap and shed water away from step flashing. While step flashing sits directly on the roof deck and shingles, counter flashing is embedded higher up in the wall or chimney and bends downward to cover the top edge of the step flashing, creating a water-shedding barrier that prevents moisture from running behind the flashing assembly.

The two pieces work together as a system. Step flashing handles water that flows down the roof slope, while counter flashing intercepts water running down the vertical surface (such as a chimney or exterior wall) and directs it outward. Without counter flashing, water trapped between the step flashing and the wall can penetrate into the structure, causing rot, mold, and interior damage.

Counter flashing is typically made from aluminum, galvanized steel, or copper, depending on the roof material and building envelope. Proper installation requires careful mortar work or siding integration to ensure the metal sits securely and remains watertight over decades of freeze-thaw cycles and weather exposure. Hartford Metro contractors often encounter varied masonry conditions when installing or replacing counter flashing, making precision fitment essential. When roof work involves chimneys, parapet walls, or other vertical penetrations, counter flashing is a critical component of the overall roof replacement or repair system.