Flashing a chimney on a synthetic slate roof involves creating a watertight seal where the chimney meets the roof surface. This typically includes two main types of flashing: counter flashing and step flashing. Step flashing consists of small, L-shaped pieces of metal that fit over the roof shingles and overlap the side of the chimney, directing water away from the joint. Counter flashing is installed over the step flashing, usually embedded into the chimney mortar joints, creating a secondary barrier that prevents water infiltration. Synthetic slate is less flexible than asphalt shingles, so flashing must be carefully fitted without excessive bending that could crack or damage the slate. Over time, flashing can corrode, pull away from the chimney, or the sealant around it can deteriorate, causing leaks.
To check your chimney flashing safely, start by using binoculars to inspect from the ground or a sturdy ladder to look for visible gaps, rust, or loose flashing. Pay attention to whether the synthetic slate around the chimney remains intact and properly overlapped by the flashing. Avoid walking directly on synthetic slate, as it can crack underfoot. If you spot signs of damage, water stains inside your home near the chimney, or suspect flashing issues, it’s time to call a professional roofer experienced with synthetic slate. When interviewing a contractor, ask if they have specific experience with synthetic slate and how they plan to seal the flashing without compromising the roofing material’s warranty. Also, inquire about the type of metal flashing they recommend to ensure long-lasting corrosion resistance.