Flashing a chimney on a polyurethane roof coating involves creating a watertight seal where the chimney meets the roof surface using both counter and step flashing. Polyurethane coatings form a seamless, flexible membrane, so the flashing must be carefully integrated to prevent leaks. The counter flashing is typically attached to the chimney itself, overlapping with the step flashing installed in the chimney’s brick or masonry joints. Step flashing is cut into individual pieces, bent at a 90-degree angle to slip under the shingles or roofing material (or in this case, beneath the polyurethane coating), while the other side lies flush against the chimney wall. On a polyurethane roof, contractors usually embed the step flashing into the coating’s edge or adhere it with a compatible polyurethane adhesive. The counter flashing is then secured and sealed with a high-quality, weatherproof sealant designed for flexible roofing systems to accommodate thermal movement. This combination ensures water is directed away from critical seams and into the drainage plane, preventing leaks or water damage.
If you want to do a simple check yourself before calling a pro, look for any signs of peeling, cracking, or separation around the chimney flashing and coating edges. This may indicate that water is getting under the membrane, which could lead to leaks. Gently run your hand over the flashing seams to see if anything feels loose or brittle, but avoid forceful probing that could damage the coating. When hiring a roofer, make sure to ask if they have experience working specifically with polyurethane roof coatings and flashing chimneys in this way. Two important questions are: “What type of flashing materials and sealants do you recommend for maintaining compatibility with polyurethane coatings?” and “How do you ensure proper adhesion and flexibility to prevent future water infiltration?” These questions help confirm the roofer’s familiarity with both the material and proper warranty-friendly installation practices.