The Roofing Resource Blog

Chimney Repair: 3 Most Common Reasons Chimneys Leak

Fri, Apr 29, 2016 @ 09:00 AM | Perry

A roof leaking around chimneys can happen for a variety of reasons such as bad flashing on the roof or porous masonry from spading bricks  and some chimneys even suffer from multiple issues that can cause leaks. Understanding why your chimney may be leaking will help you make a better chimney repair decision which can save you money. 

 

Here are the top 3 Reason’s Chimneys Leak

1. The number one most common reason you'll see roofs leaking around chimneys leak is a result of a flashing issue at the roof where it meets the chimney. Two types of flashings are used to roof around a chimney, a base flashing or step flashing is the piece or pieces that attach to the roof itself and make an L shaped bend up along the side of the chimney. The next type of flashing is called a counter flashing and its purpose is to cover the top of the step flashing and not allow water to enter behind it. The counter flashing is the part you typically see from the ground view or road view and is generally set into the masonry wall. 

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Whether you have a asphalt shingle roof or a metal roof, the chimney flashing can be one of the toughest parts of a roofing job requiring the most skill, unfortunately for homeowners not all roofing companies  know how or have experience to properly flash in chimneys. Many roofers will even skip the chimney flashing altogether relying on the old flashing to keep the new roof dry. This seldom works out well for the homeowner. 

 

Symptoms of Bad flashing around your chimney

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  • Strained ceiling around the chimney up to several feet away 
  • Soft or rotten roof sheathing around the chimney on the roof side 
  • Curled or warped shingles adjacent to and below the chimney 
  • Can allow larger amounts of water to enter home or building 

 

2.  Not as common as leaks that stem from bad flashing but still a frequent cause of chimney leaks is water infiltration related to the masonry structure and cement cap. Masonry chimneys not only take heavy abuse from mother nature sitting on the top of homes and buildings but are also subject to the moment of a structure and more thermal shock from quickly heating up and cooling off from heat rising out of them. All this can take a toll on the brick or stone itself and the mortar joints hold the masonry together. Cracks form at the cement cap and allow moisture to enter the masonry then freezing weather cause this moisture to expand and can pop the front of the brick or stone off leaving the brick even more vulnerable to water infiltration. 

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Chimney leaks related to the masonry are often slower more seeping type of leaks that may or may not occur each rain. It may take larger amounts of rain/snow to saturate the porous masonry to the point that it leaks inside. 

 

Symptoms of roofs leaking around chimney from Masonry 

  • The face of the bricks are popped off laying on the roof 
  • Brick inside the chimney turns dark after a rain then brick turns white 
  • Leaks are  usually slower 
  • Chimney may leak without staining the ceiling because the water is coming from inside the brick

 

3. The Third reason chimneys leak less common than bad flashing or porous masonry but still occurs with some frequency but is actually not a roof leak at all. Condensation can occur in chimneys and disguise itself as a leak. This most often occurs if a gas furnace or gas water heater is vented through an old chimney or it can happen in fireplaces that have gas logs and the chimney liner is cracked  which can allow the byproduct of gas combustions - H2O to bypass the liner, contact cool masonry and condense into water droplets. These drops then fall back into the chimney and appear to be a leak. 

 

Symptoms of a roof leaking around chimney from Condensation

  • Leaks when it is not raining 
  • Only leaks during a cool snap or cooler weather
  • Gas combustion vented through chimney 

Topics: Chimney Leaks, Bad Flashing