What is Chimney Flashing?

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  • Written By: Dee S.
  • Edited By: Bronwyn Harris
  • Last Modified Date: 13 September 2019
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Chimney flashing prevents water from entering at the point where the chimney and the roof meet. Typically, step flashing is used along the edges of the chimney stack. Leaks often occur at the chimney when flashing fails. Damaged flashing can be cemented or patched; however, it is also a sign that the roof may need to be replaced sooner than later. Before beginning any roofing project, it is important to wear the proper gear, such as rubber-soled shoes, protective gloves, a tool belt, and even a safety harness.

Every chimney is different, so installing chimney flashing is often a custom project. In most cases, chimneys are not attached to the frame of the house. As a result, when the house settles or shifts, the chimney becomes the perfect place for leaks. Other times that the chimney flashing will need to be replaced include when it is missing, when it is rusted through, when it is totally covered with roofing tar, or when the shingles are going to be replaced.


If the roof is comprised of asphalt or wood shingles, the chimney flashing can be replaced or installed by an experienced do-it-yourselfer. In the alternative, if the roof is made of slate or tile, the flashing techniques are much more complicated and should usually be left to a professional. Before beginning this advanced project, it is important to consider whether working on top of a roof is a comfortable scenario. In addition, metal pieces must be measured, cut, bent, and layered so that they fit tightly around the chimney and will shed water; so, do a self-check of your skills to make sure the project can be adequately completed.

Hiring someone to replace chimney flashing may cost quite a bit; however, it guarantees that the job will be done correctly and safely. Just make sure to hire a reputable contractor and someone who is insured. This is the best option for a less experienced craftsperson or someone with a fear of heights, vertigo, or other health issue.

For those who want to go out on their own and install chimney flashing, there are at least two options. A metal work shop should be able to custom cut new chimney flashing by following the pattern of the old flashing or by following specific dimensions. The other option is to cut the metal at home with special metal cutting equipment. Cutting the metal at home is the cheapest; however, it also is quite a bit of work and leaves plenty of room for error for an inexperienced metal cutter. After the metal is cut, installing the chimney flashing will take a full day for even an expert.


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Post 2

@Markerrag -- some do it yourself types can do very well with installing flashing on a chimney that is flat because it is fairly easy to seal the gaps between the flashing and the chimney.

That all goes out the window with natural stone chimneys, however. Sealing the cracks around those is tough for even a professional.

Oh, and if your flashing does start to leak, you can do a quick fix by applying caulk to it so it will reseal. Still, that is not a permanent solution. If your flashing is leaking, you'll need to get it replaced sooner rather than later.

Post 1

You had better know what you are doing if you are going to replace chimney flashing. Getting that job right is tough for even professionals on some chimneys.

If you don't get it right the first time, you risk a leak that could leave nasty water stains on your ceiling around a chimney and possible mold and mildew in your attic. Those problems are expensive to fix.

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