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What Causes Chimney Leaks?

What's Causing Your Chimney To Leak?!

Have a Chimney Leak Problem?

A leaky chimney is a common issue for homes with brick chimneys. A leak can be a troubling problem, especially frustrating because it’s a problem that can come back if the issue isn’t resolved correctly the first time.

The little drip, drip, drip of a leaky chimney isn’t just a cause of irritation; it can signify a deeper and more serious problem. Because leaky chimneys allow water to seep into your house walls, it could mean that water is in danger of damaging more of your home that just your chimney!

But what even causes these detrimental leaks into your chimney in the first place?

Brick is  naturally durable and your chimney seems structurally sound, so you may be rightly confused as to why, after a particularly rainy day, water has trickled into your chimney.

As with many other construction issues, the source of the problem isn’t usually very cut and dry. There could be several reasons affecting your brick chimney that allow rainwater to come inside your house. Your chimney crown may have cracked, the wood siding may have knots or cracks that allow water to seep through,your brick chimney may have cracked or loose mortar,  or your leak may have its origin at a different place in your roof and simply found its way down into the chimney.

However, the number one most common issue of leaking is due to a flaw in your chimney’s original design. If your home was built after 1990, and has a brick chimney with a metal flue cap which covers the whole chimney top outside, and is experiencing a chimney leak, it may have this design flaw too.
Here’s why your chimney’s leaking problem may have been so difficult to pinpoint and fix. This particular design of brick chimney utilizes a technique called the “wood chase design.” 

That means that, while many people may blame the exterior flashing for not protecting your inner chimney from the rain, the problem actually lies beneath the exterior flashing. Many times, when a leak starts but the source cannot be easily identified, roofers will opt to waterproof the brick exterior of your chimney. Sometimes an exterior modification is recommended. 

These procedures may be costly and, while it often provides a temporary solution, it’s not sustainable. Why? Because, instead of addressing the leak at its root cause (which is behind the exterior flashing), these “fixes” only prevent the water from leaking in as fast. But even with the best waterproofing system, about 10% of moisture will still escape through the brick, which is a naturally porous material.

The  water naturally seeps through the brick over time can start this leak. From there, it slips behind the exterior flashing where it starts to soak the plywood structure behind the brick. This causes blackening and rotting and also allows the water to continue to soak down until it reaches your house’s walls and begins to rot them too!

So, what is the solution to this chimney leak?

The only way to solve this issue and to prevent it from recurring in the future is to install something called an interior chimney flashing. A professional mason would strip the brick exterior construct a second flashing which runs from behind the brick at the same level as the flashing already in place. When it meets the existing exterior flashing, it will turn and go around the chimney to cover the brick and overlap the exterior flashing.

This prevents leaking because it automatically creates a little gutter-like system of trapping the incoming water and redirecting it outside of the chimney via something called a weep opening or weep hole.
Here at A and X Masonry, our skilled masons have the experience necessary to quickly diagnose your chimney leakage problem and find the cause of the leak, then give you an accurate quote. We’ll fit you into our schedule within the couple of weeks  after our initial estimation, often sooner.
So, if you’re ready to schedule a free consultation, contact us!