12 Reasons Your Chimney Might Be Leaking


Leaky chimneys are scary and not something that should be taken lightly. Not all leaks in your chimney can be seen or heard. But all leaks pose similar risks to your home and health. Constant water intrusion can work down from the chimney into the attic and to the foundation of your home causing costly damage on its way. 

Some of the unexpected dangers of a leaky chimney include: 

Attic & Ceiling Damage

A crack in your chimney can redirect water from outside into your attic. This can damage the items you have stored in there, but also damage the interior ceiling. Affected ceiling paint will change colors and the ceiling plaster may bubble and expand. 

Mold & Mildew Issues

If the leak is left alone for too long, one of the most serious consequences is the development of mold and mildew. Mold can easily spread through your home, into the HVAC system and then to the rest of the house through your vents. 

Fire Hazards

If your electrical wiring is in your attic or ceiling, water could drip and pose a fire threat from shorted wires. If you suspect water damage like this, we recommend that you turn off the electricity in that area and have an electrician examine it. 

Compromised Structural Integrity

A leaky chimney could compromise your rafters, ceiling joists, and wall framing. But chronic leaks can lead to wood deterioration. If it’s left untouched, the deterioration can cause serious problems that would need professional contractors


Symptoms of a Leaky Chimney

Many people assume that all chimney leaks present themselves as visible water in the fireplace or flue. Or that you can hear the water dripping in the puddle. Unfortunately, that’s not always the case.  

And because of the size and complexity of your chimney’s system, you probably won’t recognize you have a leak until it’s too late and it’s caused significant damage. 

Luckily, you may be able to spot some key signs that indicate your chimney may be leaking, such as: 

  • You have water or condensation inside your firebox
  • You can hear the water dripping in the chimney
  • You have moisture, leaks, or water staining on walls or ceilings around your chimney
  • You can smell musty or dank odors, especially after it rains
  • You have cracked or spalled interior or exterior masonry

You should still have an inspection annually to get ahead of any potential water damage. Remember that the five signs listed may indicate that your chimney is leaking. But they may only present themselves when it’s too late.

How the Water Gets In

There are a lot of ways that water can enter into your chimney, and this list of 12 Causes is not exhaustive. These are, however, some of the most common ways and definitely deserve to have your attention. 

1) Missing Chimney Cap

Sometimes, during the intense summer rainstorms, the wind can blow so hard that it blows your cap right off or it can knock it loose. In this case, any time it rains, you may be faced with water entering right from the top. 

A chimney cap is extremely important to keep water out. But it also helps keep leaves, bugs, and some animals out too. 

2) Cracks in the chimney crown

The chimney crown is the cement surface at the top of your chimney. If it becomes cracked, water can seep in and cause some problems. Some common reasons for cracks in your chimney crown include: 

  • Improper construction of the chimney crown
  • Your chimney structure shifted
  • Concrete shrank as the water content dried out
  • Water was absorbed into your chimney crown and went through a freeze/thaw cycle

Whatever happened, it’s important to act quickly to get the crown fixed because it’s designed to protect your chimney from harsh weather. It does this by redirecting the water to the outside of the chimney where it can fall on to the roof or to the ground.

3) Leaks from the inside out – Condensation

Dampness on your bricks and mortar of your chimney is a symptom of “Chimney Sweating.” You’ve seen condensation on your window when it’s cold outside and warm inside. This is the same thing that happens to your chimney. When it’s cold outside the warm air inside the home causes your chimney to “sweat.” 

This is actually a normal process. But sometimes your fire’s heat may not be enough to help the water evaporate. If the water stays in the chimney it can be absorbed by the porous bricks in your chimney. Then it could go through a freeze/thaw cycle, which is a very common cause of cracks. 

Once your chimney has cracks it becomes more susceptible to leaks. 

4) Defected chimney flashing

Your chimney flashing is like your chimney’s custom rain boot. It helps keep the connection between the chimney and roof watertight. But this area of the chimney is extremely vulnerable and the effectiveness of your flashing eventually expires. 

The flashing can become damaged for many different reasons, like weather and rust. Or when a roofer covers the flashing with roofing tar, which diminishes the effectiveness. 

5) Defective bricks – leaking bricks

Bricks that are used to build chimneys are usually porous. Which means they absorb water pretty easily. Like many parts of your chimney, when water enters, the bricks become susceptible to the nasty freeze/thaw cycles that cause cracks. 

6) Loose knots and cracks in the wood siding – 

If your home has wood siding, loose knots and cracks in the wood siding can contribute to your leaking chimney. Knots in the siding can come loose or the wood can dry out and split. In either case, water can seep behind the siding and leak into your home. 

7) Poorly built chimney shoulder

Your chimney’s shoulder is the area where your chimney begins to narrow. The chimney starts to narrow as the masonry is higher causing a slope. The slope can feature ledges that prevent water from draining away from the brick and stone. As you might be seeing, water and mortar aren’t necessarily a match made in heaven. Because when together, they can lead to havoc.


8) Roofing nails or Roofing Tar

Roofing nail leaks can happen when your roof nails have been loosened by high winds or have simply pulled out over time. If your shingles get lifted and expose the nail that was pulled up, the nails will begin to rust. One rusted nail is enough to cause your roof to leak every time it rains. 

Also, as I mentioned before, if your roofer places roofing tar over the flashing, it can diminish the effectiveness of the flashing.

9) Rusted chase cover

Chase covers are metal covers that fit over the chimney chase to prevent water from entering into your chimney. They are usually found on pre-fab or factory-built fireplaces. They are installed with a bit of slope so that water can run off of it. 

However, sometimes they aren’t properly installed, so water just stays on top and causes your chase cover to rust. And rusty chase covers can result in leaky chimneys. 

10) Wrong chimney liners

Chimney liners are what goes into the flue to help direct the smoke out of the fireplace. Your liner needs to be sized specifically based on the appliance that it is covering. If the flue is too big, flue gasses will begin to condensate and cause excess moisture to build up (and we mentioned that at #3). 

11) You May Need a Chimney Cricket

If your chimney is located on a downward slope of your roof, it’s likely that water pools around the base of your exterior chimney where it meets your roof. As you can guess, this pooling of water can seep into the bricks and mortar, causing serious damage and deterioration of your chimney. 

A chimney cricket is a small peaked roof which is installed on the backside of your chimney to help deflect water from your chimney. It can be made from steel (galvanized or stainless), or aluminum. 

12) Worn out brick and mortar joints

One of the most vulnerable parts of your whole chimney is perhaps the brick and mortar joints. They go through a lot of stress from excessive exposure to the weather. And when the joints get damaged and split, chimney leaks are a very common problem. 

How Do We Fix the Leak

Each leaky chimney gets its own customized rehab plan to get it back to safety. In other words, there’s no “one size fits all” type plan, but here are the 5 most common things we do to help fix your chimney. 


If your chimney’s bricks are in good shape, then we may suggest repointing. The process of repointing starts with grinding out the mortar joints between the brick. Then the joints are filled back in with new mortar. 

Add a chimney cap

We will get a cap that’s custom fit to your chimney and add that on. If you already have a chimney cap, but it got damaged somehow by the weather, then we’ll inspect it to make sure it is still safe to use. But most of the time, you’ll need a new one. 

Fix the flashing

The first thing that we’ll do is clean away any debris, like leaves or sticks. Then we’ll use ChimneySaver FlashSeal, which comes with a seven-year warranty, to cover the flashing. We will apply a base coat that covers the entire flashing area. Then we will add a reinforcement fabric and cover the fabric with a top coat of the FlashSeal.

Apply waterproofing

At Patriot Chimney, we use a water-based water repellant. This way the repellant can seep into the pores of the brick. The product we use reduces water penetration in the bricks by 99.9%. It is also 100% vapor permeable, which means it won’t trap water vapors when your chimney is in use (remember #3?). 

But I should mention that waterproofing does lose its effectiveness over time. We recommend that you reapply waterproofing every five years for optimum performance. 


When your chimney has more serious damage that’s causing leaks, we will recommend that you have your chimney repaired. This could be fixing the cracks in the bricks or the cracks on the crown. But it could be something more serious like replacing whole bricks. 


Preventing Chimney Leaks

You probably don’t want to hear it, but the best way to ensure your chimney doesn’t leak is by having it inspected by a CSIA certified technician. Annual inspections help to identify any new chimney or masonry damage. At Patriot Chimney, we keep strong records of all of our inspections so that we can spot changes from year to year.

Some people think that if they aren’t using their fireplace that often, then they don’t need to worry about an inspection. This isn’t true. Whether you use your chimney or not, it is still exposed to the elements and can easily deteriorate through time and cause more substantial damage.

Another huge way to prevent your chimney from leaking is to add repointing and waterproofing into your preventative maintenance budget for your home. Both the mortar and waterproofing are bound to deteriorate over time. So it’s important to keep them in tip-top shape.


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