Flashing a chimney on synthetic shake roofing requires careful attention to create a watertight seal where the roof meets the chimney. The process involves installing two main types of flashing: counter flashing and step flashing. Step flashing is placed along the chimney’s sides, tucked under each row of synthetic shake shingles, overlapping in a stair-step pattern. This guides water down the roof surface without allowing it to seep behind the shingles. Counter flashing covers the upper edge of the step flashing and is embedded slightly into the chimney’s mortar or attached securely to its sides, forming a continuous barrier to prevent water ingress. Problems usually arise because synthetic shakes are thicker and have different flexibility compared to traditional shingles, so improper flashing can create gaps or stresses where water can enter.
For a simple DIY check, look for any visible gaps, rust, or cracked caulk around the flashing edges, especially after heavy rain. You might gently lift some shakes on the lower rows near the chimney to ensure that step flashing is properly tucked underneath, but avoid forcing or damaging the synthetic material. If you notice water stains inside your attic near the chimney or signs of mold, it’s time to call a professional roofing contractor who is familiar with synthetic roofing products and the building code requirements for flashing. When engaging a contractor, ask specifically how they plan to attach the counter flashing to the chimney without harming the synthetic shakes and whether they will use compatible sealants that won’t void your roofing warranty. This ensures proper installation without compromising the integrity or appearance of your roof.