If we had to identify a single component responsible for more roof leaks in Boise 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.
Why Chimney Flashing Fails in Boise's Climate
Idaho's freeze-thaw cycles are particularly hard on chimney flashing because brick and mortar expand and contract at different rates than the metal flashing embedded in it. Over years, this differential movement works the counter-flashing out of the mortar joints and separates the seals. A chimney that was perfectly sealed at installation may develop gaps after 10 to 15 years.
What a Proper Chimney Flashing Repair Includes
A complete chimney flashing repair involves removing the existing counter-flashing, cleaning out the old mortar joints, embedding new counter-flashing with fresh mortar, confirming or replacing step flashing behind the counter, and applying appropriate sealant at all transitions. A patch of sealant applied over existing flashing without addressing the underlying failure will fail again within one to three years.