Common causes of chimney leaks – Family Roofing

Posted on by David Reid

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Common causes of chimney leaks

Any water inside a chimney system is a leak and all water can damage a chimney structure and its components. Most of the time, a leaky chimney starts with:

No Cover On Top of Your Chimney

One of the biggest causes for leaking chimneys is that you don’t have anything covering the top.  With no chase cover, crown, cap or damper, your chimney has no way of protecting against rain and snow from entering it.  Not only can moisture enter your chimney with no cover, but birds and other animals have a free passageway into your home.  It only makes sense to have a chimney cover.  Plus, if your chimney gets backed up from moisture and other debris, smoke can billow back into your home.  Smoke and carbon monoxide can quickly take over your home which we all know is extremely dangerous.

Damaged Chimney Crown or Chimney Cap

Another very common cause for chimney leaking is a damaged or cracked chimney crown or cap.  Your chimney crown is the concrete slab on the top that protects your chimney from the weather.  Over time, the concrete can become brittle and crack due to the excessive amount of moisture and temperature changes it experiences.  Fixing chimney leaks caused by a damaged chimney crown can be repaired by filling the cracks or completely replacing the crown.  Chimney caps are found on prefabricated or factory-built chimneys.  If your home still has the original chimney cap on it, chances are it’s made of galvanized steel which can rust and crack over time.  In such a case, you should replace it as soon as possible with a stainless steel, copper or aluminum chimney cap to make sure it never rusts again.

Worn Out Brick and Mortar Joints

Perhaps the most vulnerable area of your chimney are the brick and mortar joints which undergo a lot of stress from excessive exposure to weather.  When the joints get damaged and split, chimney leaks become a common problem.  If you notice water leaking through your chimney but you know everything else is in good condition, then your brick and mortar joints are most likely the culprit.  You must get them repaired as soon as possible because if the leaking continues, your chimney’s structural integrity is at stake.  Chimney tuckpointing and waterproofing will get your mortar joints back to new and your chimney will be moisture free.

Flashing that is Rusted or Missing may let Water In

Flashing is an important component if you want to prevent a leaking chimney.  This metal is used to direct water away from the opening where the chimney comes through the roof.  If the flashing is rusted or missing, or if the sealant no longer seals the materials completely, then you could end up with water coming in where you do not want it.  Flashing is used to seal and protects joints in a building from water penetration by direct the flow of water away from these otherwise vulnerable areas.  For Flashing to function properly it is important that it is installed correctly.

Using the Wrong Material to Waterproof Bricks

Sometimes a leaking chimney is caused because the material used for waterproofing the bricks is not the right product.  The waterproofing material should not block up the pores of the brick or block of the chimney, because this can prevent evaporation and cause water to build up.  Applying a waterproofing product designed for chimney bricks will eliminate the cause of this type of leak.

Chimney Condensation

One of the more rare cases of chimney leaks is condensation building up inside and causing it to leak through.  Chimney leaks caused by condensation happen when a chimney is converted from wood burning to gas burning and isn’t fitted with the proper liner.   Gas fireplaces give off fumes with moisture due to the lower temperatures and of the correct liner isn’t installed, that moisture can build up and seep through your chimney walls.

What to do about a leaky chimney

Inspection is the first step in dealing with a chimney leak.  A chimney inspector will evaluate your system and provide a report showing exactly what was found.  The inspector in most cases will be able to make needed repairs including:

  • Brick replacement

  • Tuckpointing to replace decayed mortar joints

  • Chimney crown rebuilding

  • Chimney cap repair or replacement

  • Chimney flashing repair or installation

  • Complete or partial chimney rebuilding when the chimney damage is severe

A leaking chimney isn’t something you want to ignore.  Leak issues don’t resolve themselves; rather, they progress to unsafe conditions.