Flashing a chimney on 3-tab shingles involves two main types of flashing: counter flashing and step flashing, which work together to create a watertight seal where the chimney meets the roof. Step flashing consists of small, L-shaped pieces of metal that are installed in layers with the shingles along the side of the chimney. Each piece overlaps the shingle below and fits against the chimney, directing water away from the joint. Counter flashing is installed on the chimney itself, covering the top edge of the step flashing and embedded into a groove or mortar joint on the chimney to prevent water from getting behind the steps. Flashing failure often results in leaks, which happen due to improperly sealed joints, damaged flashing, or poor installation that allows water infiltration. To check flashing yourself, inspect around the chimney for signs of rust, gaps, or loose metal, and watch for water stains or damp spots inside the attic after a rain. Ensure shingles around the chimney are flush and securely fastened without cracks or missing pieces.
If you notice damaged or missing flashing, or persistent leaks even after you repair shingles, it’s best to call a professional roofer since chimney flashing requires precise installation to prevent water damage and maintain warranty coverage. When consulting a contractor, ask whether the flashing will be integrated with new flashing boots or sealants to extend durability without compromising the shingle warranty. Also, clarify if they’ll embed the counter flashing in the mortar joints with copper or aluminum flashing that can resist corrosion. Confirming these details upfront can help ensure a long-lasting, leak-free roof-to-chimney transition that protects your home efficiently.