Water appears on the ceiling near the chimney. A roofer replaces the flashing. It leaks again. The homeowner concludes the roofer was incompetent, and sometimes that is true — but often the flashing was fine and the water is coming through the chimney itself.
Masonry is not waterproof. Brick and mortar are porous, and a chimney is a tall stack of them standing fully exposed with a large horizontal surface on top. In a climate delivering roughly 150 days of precipitation a year, that is a demanding assignment.
The crown is the sloped surface capping the top of the masonry around the flue. Its job is to shed water outward past the face of the brick. It is also the most exposed element on the entire building.
A great many crowns, particularly on older homes, were built from ordinary mortar rather than proper concrete, without reinforcement, and without an overhang or drip edge to throw water clear. Mortar crowns crack. Once cracked, water enters the top of the chimney directly and travels down inside the masonry, emerging at the ceiling wherever it finds a path out.
You can often see the problem with binoculars from the ground: visible cracking across the crown, missing sections, or a crown that is flush with the brick face rather than projecting beyond it. This is the first thing to check when a chimney leaks and the flashing has already been addressed.
An uncapped flue is an open pipe pointing at the sky. Rain goes straight down it. Water then reaches the smoke chamber and firebox, where it can damage the liner, corrode the damper, and produce staining and odour inside the house, particularly noticeable in damp weather.
A cap is inexpensive and also keeps out birds, rodents, and debris. Missing caps are common on chimneys serving fireplaces that have not been used in years, precisely because nobody is paying attention to them.
Mortar is softer than brick by design, and it weathers first. Over decades the joints recede, develop hairline cracks, and eventually lose material. Each degraded joint is an entry point, and a chimney has a great many of them.
The repair is repointing — grinding out the failed joints and refilling with appropriate mortar. Worth noting: mortar hardness must be compatible with the brick. Modern high-strength mortar used on soft historic brick causes the brick itself to spall, because the joint becomes harder than the masonry around it and stress relieves through the softer material. On older Seattle homes this is a real consideration and an argument for someone who works with historic masonry rather than a general handyman.
Spalling is where the face of a brick flakes, crumbles, or pops off. It happens when water absorbed into the brick expands — classically through freeze-thaw, which Seattle does experience, if less often than colder regions.
Once the fired outer face is gone, the exposed interior is far more absorbent than the original surface, so the process accelerates. Extensive spalling means the masonry is taking on significant water, and it is a structural trajectory rather than a cosmetic one.
A few useful indicators.
Where the water appears. Flashing failures typically show at the ceiling immediately adjacent to where the chimney passes through. Masonry absorption more often shows lower — on the chimney breast in a room below, or as damp on the interior masonry face itself.
Timing. Flashing leaks tend to appear during or shortly after rain. Masonry absorption leaks often lag, appearing after a prolonged wet period rather than a single event, because the masonry has to saturate before it passes water through.
Wind direction. If the leak correlates with wind-driven rain from a specific direction, that points toward the exposed face of the masonry rather than the flashing.
Isolated water testing. The definitive method. Wet only the flashing at the base, wait, observe. Then wet only the lower masonry. Then only the upper stack and crown. Each in isolation, with dwell time between. Chimneys are the single best argument for careful component-by-component testing, because there are four independent suspects within a few feet of each other.
The cricket. On the uphill side, a chimney dams everything running down the slope above it. Code requires a cricket where the chimney exceeds 30 inches on that side, and under Seattle's tree canopy it is good practice well below that width, because the alternative is a permanent trap collecting conifer needles and holding them wet against the masonry.
Framed chases. Many newer homes have a chimney chase — a framed and sided enclosure around a metal flue rather than a masonry stack. These leak at the chase cap on top, which is typically sheet metal and frequently installed flat with no slope, so it ponds. A flat chase cap with standing water on it is a leak waiting for its moment.
Worth being direct: crowns, repointing, spalling, and liners are masonry and chimney work, not roofing. A roofer can and should identify them, and can address flashing, cricket, and the roof-side details. But if the diagnosis lands on the masonry, the right specialist is a chimney or masonry contractor, and a roofer who tells you that is giving you accurate advice rather than turning down work.
This post is part of our in-depth coverage of roof repair & leak detection in Seattle.
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