Flashing a chimney on exposed fastener metal roofing involves installing both counter flashing and step flashing to create a watertight seal where the chimney meets the roof. Counter flashing is the vertical piece that covers the top edge of the step flashing, which runs along the side of the chimney and under the metal roofing panels. The exposed fastener metal roof means screws or nails are visible, so it’s crucial to ensure those fasteners are sealed properly to prevent leaks. This type of roofing makes flashing different from shingles because you can’t just lift shingles to slip in flashing; instead, you need to carefully slide the step flashing under the metal panels while overlapping and sealing around fasteners. The flashing materials are usually metal—aluminum or galvanized steel—to match the roof and withstand the elements.
To check your chimney flashing at home, look closely for any signs of water stains, rust, or loose flashes, especially around fasteners that may have lost their rubber washers. Run your hand along the joint for any roughness or gaps where water could penetrate. A simple DIY way is to use a hose to simulate rainfall and watch for leaks inside the attic near the chimney. If you notice recurring moisture, corrosion, or if flashing is visibly damaged or improperly overlapping your metal roofing, calling a professional roofer is wise. When you speak with a contractor, ask if they will custom-fabricate the step and counter flashing to fit your chimney correctly and if they guarantee the fastener sealing to prevent leaks. Also, inquire about their experience with exposed fastener metal roofs to ensure they understand the unique challenges and warranty considerations.