Chimney Flashing
A two-part flashing system at chimney-roof intersections: step flashing at the sides and counter flashing embedded in the mortar joints above.
The Two-Part System
Chimney flashing is actually two separate pieces working together: step flashing, which is woven into the shingle courses along the chimney's sides, and counter-flashing (or cap flashing), which is embedded into the chimney's mortar joints and folds down over the step flashing. Together they create a shingled, overlapping barrier that sheds water away from the chimney instead of letting it wick sideways into the joint.
Why It Fails First
Chimneys move independently of the roof structure as the house settles and the masonry expands and contracts with temperature swings — the roof deck doesn't. That constant, tiny relative movement works the sealant and solder joints loose over 10–15 years, which is why chimney flashing is one of the top three leak sources we find on service calls in Fairfield County, right behind pipe boots and valley flashing.