7 Steps to Accurately Find the Source of a Chimney Leak

man working on chimney flashing

If you suspect your roof has a leak around the chimney it’s crucial to repair it as soon as possible. Unfortunately, accurately finding the source of the leak around the chimney can be a difficult task. We’ll clearly outline the tools and steps necessary to properly identify the source of a chimney leak.

Gather the following tools to help find the leak

All roof projects should be done with at least two people. Not only is it much safer, having two people makes the process much easier.

  • Communicate with the other person either through cell phones or walkie-talkies. Yelling to one another isn’t an effective way to handle the project.

  • Two water hoses with shut-off nozzles on the roof.

  • A roll of clear plastic long enough to wrap around the chimney a few times

  • A bright marker or crayon

  • Rubber-soled shoes and safety harness

Time to find the leak!

chimney on roof undergoing repair

After you have the following items, follow these next steps to accurately pinpoint the source of the leak.

1. Start by wrapping the chimney with the plastic wrap about a 1/2 inch above where the chimney meets the roof. Continue wrapping till about 18 inches up. Make sure to leave the flashing around the base of the chimney exposed.

2. With one person on the roof and the second in the house (either in the attic or watching the ceiling), turn on the hose and let the water run down the lowest side of the chimney. Let the water run for at least two minutes before shutting it off. Let it run naturally; do not aim it up at the chimney bricks or directly into the flashing.

If the second person inside the home sees any water penetration, immediately mark the spot of the hose with a bright marker or crayon. Mark the spot prominently as it may be a few days before any repairs occur.

3. If no leak is identified at the lowest end of the chimney move the hose up one shingle at a time. Give it some time before turning the water back on. Just be sure to not let the water get behind the chimney yet.

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4. Repeat this process along the other side of the chimney. Stop and clearly mark any spots of a leak, but continue the process. It’s very possible more than one source exists.

If the leak is causing water to pool in the ceiling drywall, turn off the hose and have the second person poke a small hole in the center of the spot to let it drain. Don’t run any more water until the spot has at least dissipated.

5. If neither side leaks, repeat the process along the backside of the chimney. But don’t get water up along the vertical part yet. If all sides of the chimney yield no results, the leak is higher than the base flashing or the roof shingles.

6. Reapply the plastic wrap so that the upper sections of the flashing are exposed, but the vertical bricks are covered. Carefully run the water along each side of the upper chimney flashing, and make sure to pause before moving onto the next section.

If the leak is still unidentifiable, the leak is most likely in the mortar joints, mud cap, or chimney bricks.

7. Finally, remove the plastic wrap and repeat the pattern of water application along each bricklayer until you’ve found the source of the leak. If still no signs are found, the leak is almost assuredly coming from the mud cap or mortar joints.


Hire a qualified contractor to fix the leak

Roofer cutting shingles

The point of such a slow, painstaking process is to isolate the location to almost 100% certainty.

It’s a time-consuming process but will accurately pinpoint the source of the chimney leak.

Once you're confident about the source of the leak, contact a roof repair contractor. Here at Hometown Roofing Contractors, we make it easy to choose an experienced roofer for your chimney leak repair. Customers can research multiple choices, request quotes, and see what other homeowners have to say about their contractor experience. 

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