Cap flashing, also called counter flashing, is the upper piece of a two-part flashing system that's built into a mortar joint or reglet and folds down over a lower base flashing to keep water from working behind it.
Roof-to-wall and chimney-to-roof intersections typically use two pieces of flashing working together: a base flashing tied into the roofing below, and cap flashing set into the masonry above it and bent down over the top of the base piece. That overlap is what actually sheds water, since it lets the roof and the wall move slightly against each other without opening a gap. Cap flashing is usually let into a cut reglet joint in the brick or stone and sealed, rather than just caulked to the face, so it stays put through temperature swings.
Cap flashing that's been caulked to the surface instead of properly let into the masonry is one of the most common shortcuts we find on chimney repairs, and it's also one of the first things to fail, since caulk dries out and cracks long before properly set flashing does. Once that seal opens, water tracks straight down behind the chimney brick, and you get the same freeze-thaw damage as any other water intrusion point, just hidden until the brick starts popping.
More masonry vocabulary from the glossary.
The services where this term comes up.
Chelo's Brick & Stone serves Hillsville, Galax, Wytheville, Fancy Gap, and Independence, VA. Call for a straight answer and a free on-site estimate.
