Chimney Leak Repair in a 156-Rain-Day City

Seattle's rain is not heavy so much as constant. NOAA's 1991 to 2020 normals put Sea-Tac at about 39 inches a year spread over roughly 156 days with measurable rain. Everett's Paine Field gets less rain in total but logs it on about 178 days, and Tacoma Narrows averages about 42 inches. For a chimney that means long stretches when the brick, crown and flashing never fully dry.

That steady wetting finds every weakness. A crown with a hairline crack, a cap with a torn screen, flashing sealed with tar twenty years ago, or brick so porous it wicks water inward like a sponge. Most leaks we trace have more than one cause, which is why fixing only the first one found so often fails. The leak check is free.

Signs you need this

• Water dripping onto the damper or pooling in the firebox
• Brown stains on the ceiling or wallpaper beside the chimney
• A musty smell from the fireplace after a few days of rain
• White powder or dark damp patches on brick inside or out
• Moss covering the crown, the brick or the roof by the chimney

How we do it

1. Trace the waterWe check the cap, crown, brick, mortar and flashing from the roof, then the firebox and attic from inside.
2. Photograph every entry pointYou see each place water gets in, with a written price for each fix, so the leak is solved rather than chased.
3. Fix from the top downWe work in order: cap and crown first, then flashing, then joints and brick, so each layer sheds water onto a sound one.
4. Protect the brickWhere brick is porous, a breathable water repellent lets moisture out while keeping rain from soaking in.

Where do Seattle chimney leaks usually start?

The cap is the simplest. With no cap, or a rusted one, rain falls straight down the flue. Next is the crown, the slab on top of the brick. A cracked or thin mortar crown lets water into the top courses, and it often shows up as a drip at the damper. Then the flashing, the metal seal between brick and roof. Failed flashing shows up as a ceiling stain beside the chimney rather than in the fireplace.

The last is the brick and mortar themselves. Old brick and worn joints absorb rain, and after weeks of wet weather that water can come through to the inside. Moss holds the surface wet even longer, which Oregon State University Extension notes for roofs and which holds just as true for masonry and flashing.

What does chimney leak repair cost?

A cap, crown or sealing fix is typically $300 to $1,000. Flashing or masonry repair is typically $800 to $2,500. Many leaks are solved at the lower end once the real entry point is found.

A breathable water repellent on the whole stack is typically $300 to $800. We only suggest it when the brick itself is taking on water, and only after the crown, cap and flashing are sound, because a repellent cannot stop water coming in from above.

Should I seal the whole chimney to stop the leak?

Not with just any sealer. The National Park Service's Preservation Brief 2 explains that masonry has to let moisture out, or the brick is damaged as water and salts build up behind the surface. Film-forming coatings and paint can do exactly that, trapping water that later freezes and spalls the brick face.

A breathable repellent is different. It sheds liquid rain but still lets water vapor escape. Used on sound brick, after the real leak points are fixed, it helps an old chimney stay drier through a long wet season.