Why is my chimney leaking?

This time of year, as snow piles on rooftops and chimneys get pelted with rain sleet and snow, many homeowners see concerning puddles of water within their fireboxes, water stains around their chimneys on ceilings and walls or rust forming on fireplace doors, dampers or grates. Seeing signs that your chimney is leaking can be both frustrating and terrifying. Water damage can be expensive to fix, but before you can work toward a repair, first you have to know why the chimney is leaking. Here are a few likely culprits.

What causes chimneys to leak?
What causes chimneys to leak?

Over time, water breaks down your chimney’s masonry, which can lead to chimney leaks. Masonry, including your chimney bricks or stones and the mortar that holds them together, is porous. It absorbs water every time it rains, snows or sleets. When temperatures drop, the water held inside your chimney masonry freezes and expands, which causes the masonry itself to crack or crumble away. The holes and cracks in your masonry can allow water to leak into the chimney itself, where it can cause water damage inside your chimney flue and in your firebox.

Failing or inadequate chimney crown

Every chimney should be topped with a sturdy chimney crown, constructed from high-quality concrete reinforced with rebar. Many chimney crowns are constructed hastily with the same mortar the mason used to build the chimney structure itself. These insufficient chimney crowns break down quickly, forming cracks that allow water to leak down into your chimney’s inner structure. Even well-constructed chimney crowns will break down over time, due to the freeze-thaw cycle, and a chimney crown that isn’t protecting your chimney from water and directing water away from your flue can cause serious water damage to your chimney and your home.

Faulty flashing

Often a “chimney leak” isn’t the chimney at all; it’s the chimney flashing. Flashing surrounds the base of your chimney, where it meets your rooftop. Sometimes flashing isn’t adequately built into the layers of the chimney and roof to form a tight seal, or flashing can crack and corrode over time. Faulty flashing allows water to drain in around the chimney. A chimney leak caused by faulty flashing often causes dark water marks on the ceiling around the chimney, or it can cause paint or wallpaper to pucker and peal. Fault chimney flashing can cause major damage in your home, as it gives water access to your home’s structure, which can lead to warping and rotting.

Missing chimney cap

Your chimney needs a chimney cap, a small metal roof-like structure that prevents water from rolling directly down your chimney flue. Without a chimney cap, water flows freely down your chimney when it precipitates. Water inside your chimney can cause water damage to flue tiles or the masonry within your chimney box, or it can cause your chimney damper, fireplace doors or fireplace grate to rust.

Nothing can be more intimidating to a homeowner than a leaky chimney because leaky chimneys can cause extensive water damage that can be very expensive to repair. If you notice signs of water leaking in, through or around your chimney, don’t wait to have it addressed — Call the Chimney Care Co. to schedule an appointment today!



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