What Is Counter Flashing?

Roofing metal at a wall works in two layers. Base flashing sits on the roof and turns up the wall. Counter flashing is set into the wall, or fastened to it, and hangs down over the top of the base flashing the way one shingle laps the one below. On brick or stone, a groove is cut into a mortar joint, the metal is tucked into it, and the joint is sealed. On other walls, a surface-mounted piece is fastened and sealed along its top edge. Because the two layers are separate, the roof and the wall can settle and move independently without tearing a seam.

Chimneys are where most reps meet it. A ceiling stain shows up near the brick, and a thick line of sealant along the joint shows the spot has been patched before. Sealant alone is maintenance, not a repair of the flashing detail. A proper reflash replaces the step flashing and sets new counter flashing into the mortar. In storm claims, wind and hail rarely destroy this metal, so expect it to be treated as age-related unless the adjuster documents storm damage.

Counter flashing, cap flashing, and reglet flashing get used loosely for the same idea, and the label matters less than the structure: a second piece has to overlap the first. The common errors are cutting the groove too shallow to hold the metal, relying on sealant to do the lapping, and leaving old counter flashing in place on a new roof because it is hard to remove from the masonry.