Leaking Chimneys

Posted on August 16, 2016


It never fails… after an extremely hard rain or after several rainy days I will get multiple calls from people who are dealing with leaky chimneys.  Often they are exasperated by a leak that roofers and masons seem to diagnose, only to have the same problem the next time a hard rain comes again.  In this blog, I’m going to address the most common form of leak that we at Alexander Masonry, Inc. address here in Central Indiana.

The Indianapolis area has experienced a boom in new construction over the past two decades.  Over 150,000 new homes were built in the area during that span and most of them have brick on at least part of the home.  Of those homes many have brick chimneys built with what masons call the “wood chase design.”  These chimneys have brick on the exterior surrounding a wood interior, with galvanized flue in the center to keep the hot gases away from the wood structure.  They are easily identified by the metal flue cap covering the entire top of the chimney.  If your home was built after 1990, has a chimney leak that has been hard to diagnose and has the wood chase design with a metal top, (as pictured below) there is a very good possibility that your problem is being described below.

The leaking problem with these chimneys comes from a faulty design.  It was common to many regional and national builders at the time. Our area had whole neighborhoods where the brick was stripped off of every chimney and rebuilt due to leaks!  The builders did not account for the fact that water does penetrate the brick and can easily get to the back side and enter the space between the brick and exterior plywood.  From there, it runs down the backside of the brick, down behind the exterior flashing, and eventually finds the wooden under structure.  Two things begin to happen.  Wherever the underlying wood gets wet, it begins to blacken and rot.  Secondly, water continues to seep downward until it enters the house and begins to soak the inside drywall.

Many times the exterior flashing is blamed, but after some sort of modification or caulking of the flashing the problem always returns.  Why?  Because the water is BEHIND the exterior flashing.  Often as the brick is found to be the problem, someone recommends waterproofing the brick.  This is somewhat of a temporary solution because a water-proofer will repel about 90% of the moisture.  But 10% of a heavy steady rain is significant and water-proofers have a limited lifespan. (about 4 years with the extremes of weather here in Indiana.)  Once the water-proofer wears off, the leak returns in full force.  Below are photos of one of the many chimney leaks of this kind that we have repaired in our area.

leaking chimney hendricks county, IN

As you can see water is rotting the underlying wood

chimney leak Zionsville, IN

chimney repair Zionsville, IN

Another view of the plywood rot                                           Plywood needed replacing

Our solution is to strip off the brick on these chimneys and install an interior flashing.  This flashing will run behind the brick all the way from the top down to the course of brick at the same level and the exterior flashing.  The flashing then turns and covers the brick and slightly overlaps the exterior flashing.  This serves to trap all water that has reached the space in between the brick and wood chase and redirect it outward through a weep opening.

Interior flashing Chimney

 Chimney after the interior flashing has been installed

Once this is done the chimney can be re-bricked and the problem is solved.  Finding a close brick match is critical for a good looking repair.  We at Alexander Masonry, Inc. have performed many of these chimney repairs over the years.  We are proud to have solved this leaky chimney problem and have a long list of satisfied customers!

chimney leaks Indianapolis

     Good as new and leak solved!!!

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