Chimney Flashing Repair in Seattle, WA

The material you choose for chimney flashing determines how long it will last and how well it withstands Seattle's relentless moisture. Aluminum is the most commonly used flashing material in residential construction. It's lightweight, easy to form, corrosion-resistant, and affordable. For most Seattle homes, aluminum flashing provides 20-30 years of reliable service. It's our standard recommendation for composition (asphalt shingle) roofs. The main drawback: aluminum can fatigue and crack where it bends tightly, especially at step flashing transitions. Galvanized steel is stronger and stiffer than aluminum, making it better for high-wind areas like West Seattle and Magnolia. It handles structural stress from heavy snow loads better than aluminum. However, the galvanized zinc coating eventually wears off in Seattle's constant moisture, leading to rust. Lifespan: 15-25 years depending on exposure. We recommend galvanized steel for chimneys in high-wind zones paired with regular inspection. Copper is the premium choice and the most durable flashing material available. Copper flashing lasts 70-100+ years, develops a protective patina that resists further corrosion, and solders beautifully for watertight joints. It's the standard for historic home restoration in Capitol Hill and Queen Anne. Cost: 3-5x more than aluminum, but essentially a lifetime installation. Lead was the traditional gold standard for counter flashing because it molds perfectly into irregular mortar joints. Lead is still used selectively for counter flashing applications where conformability matters most. However, lead is increasingly being replaced by lead-coated copper or flexible aluminum alternatives due to environmental concerns. We use lead only when it's the technically superior choice and always install it in compliance with Washington state environmental guidelines.

Seattle's diverse housing stock means our flashing technicians work with every roof type — and each presents unique challenges at the chimney junction. Composition (asphalt) shingles are the most common roof in Seattle and the easiest for flashing integration. Step flashing pieces interweave with each course of shingles, creating overlapping layers that shed water naturally. Counter flashing is set into chimney mortar joints and overlaps the step flashing by at least 3 inches. Standard installation. Cedar shake and shingle roofs are iconic in Seattle neighborhoods like Wallingford, Phinney Ridge, and Ravenna. Cedar's irregular thickness and texture make flashing integration more challenging — each step flashing piece must be custom-fitted to the shake course above and below it. We frequently see failed flashing on cedar roofs where a roofer used flat stock designed for composition shingles. Cedar also expands and contracts more dramatically with moisture changes, putting additional stress on flashing joints. Metal roofs (standing seam) are growing popular in the Seattle metro area for their longevity and rain-shedding ability. Chimney flashing on a metal roof uses a different technique entirely — flashing must be mechanically fastened to the roof panels (not woven in) with proper expansion allowance. The standing seams themselves must be cut and terminated properly around the chimney base. Improper metal-roof flashing is a common source of leaks in newer Seattle homes. Flat or low-slope roofs are common on mid-century homes in Shoreline, Lynnwood, and parts of North Seattle. Chimney flashing on a flat roof requires membrane integration — the flashing must tie into the roofing membrane (TPO, EPDM, or modified bitumen) with proper lapping and adhesion. Water doesn't gravity-drain away from a flat-roof chimney like it does on a pitched roof, making flashing even more critical. We use specialized boot flashings and membrane-compatible sealants for flat-roof chimney work.

We understand the temptation to save money with a DIY flashing repair — a tube of caulk from the hardware store seems like a quick fix for a chimney leak. But chimney flashing repair is consistently one of the most botched DIY projects we see in the Seattle area, often turning a $400-$800 professional repair into a $3,000-$5,000 water damage restoration. Here's why. Caulk is not flashing. The most common DIY mistake is slathering roofing caulk over failed flashing joints. Caulk shrinks, cracks, and peels within 1-3 years in Seattle weather. It creates a false sense of security while water continues entering through cracks and gaps. Worse, caulk can actually trap water behind the flashing by sealing the drainage paths that allow incidental moisture to escape. Counter flashing requires mortar cutting. Proper counter flashing is set into a groove cut into the chimney mortar joints with a masonry saw, then sealed with high-grade polyurethane sealant. This requires specialized tools (angle grinder with diamond blade), experience working at roof height, and knowledge of masonry construction. A DIY attempt with a screwdriver and caulk gun won't replicate this. Step flashing requires partial roof disassembly. To properly replace step flashing, the shingles or shakes along the chimney must be lifted or partially removed to weave in new flashing pieces. This is skilled work that risks damaging shingles, breaking seals, and voiding roof warranties if done incorrectly. Safety is a real concern. Chimney flashing work means operating on a roof, often near edges and on slopes. Professional chimney technicians use harnesses, roof anchors, and proper ladder staging. Falls from residential roofs are one of the leading causes of serious home-improvement injuries. The cost math favors professional repair. A professional flashing repair in Seattle costs $400-$1,200. A water damage repair from failed DIY flashing costs $3,000-$10,000+ (drywall replacement, mold remediation, insulation, paint). One winter of leaking from a bad DIY job can cause more damage than the cost of 10 professional flashing repairs. Our advice: get a professional assessment first. If the issue is a simple sealant failure at one joint, we'll tell you — and fix it for under $200. If it's systemic flashing failure, we'll quote a proper replacement and explain exactly why.