If we had to identify a single component responsible for more roof leaks in Boise homes than any other, chimney flashing would win by a significant margin. Every home with a chimney has multiple transition points where the roof surface meets the chimney masonry, and every one of those transitions is a potential water entry point. In Idaho's climate, they're under constant mechanical stress that most other roofing components don't face.
Why chimney flashing fails in Idaho's climate
Brick and mortar expand and contract at different rates than the metal flashing embedded in them. In Boise's freeze-thaw climate, those materials are cycling through that expansion and contraction many times each winter. Over years, the differential movement works the counter flashing out of the mortar joints where it's embedded and opens gaps at the base of the chimney where step flashing meets the masonry.
The problem is compounded by age. Mortar joints in older chimneys become porous and absorb water, which then freezes and expands, accelerating the failure. A chimney that looked solid five years ago can have significantly deteriorated joint integrity after a harsh winter cycle. This is why chimney-related leaks are common in Boise's established neighborhoods where homes have original or aging masonry.
Installation quality matters enormously. Proper chimney flashing involves two separate components: step flashing woven into the shingles along the sides of the chimney, and counter flashing embedded in the mortar joints above it that overlaps the step flashing. When both are correctly installed and the counter flashing is properly seated in cut joints filled with roofing cement, the system is durable. When contractors skip the counter flashing and rely on surface-applied caulk or roofing cement as the sole seal, failure is a matter of when, not if.
What a proper chimney flashing repair includes
Removing the existing failing flashing completely is the first step. Leaving old flashing in place and layering over it is one of the most common shortcuts we see on homes that have had multiple prior "repairs" that each lasted a season or two.
Repointing deteriorated mortar joints before installing new counter flashing ensures the new metal has solid material to seat against. On older Boise homes with lime-based original mortar, this step is particularly important because modern Portland cement mortar has different expansion characteristics and needs to be applied carefully to avoid accelerating future joint failure.
New step and counter flashing installed using 26-gauge galvanized steel or copper, properly woven into the shingles on the step flashing side and mechanically embedded on the counter flashing side, creates a system that handles thermal movement without relying on caulk as the primary seal. Caulk is used only as a secondary backup, not as the structural connection.
Blue Goat Roofing performs chimney flashing repairs throughout Boise, Meridian, Eagle, and Nampa. Every repair includes written documentation and a condition assessment of the surrounding roof area.