Fix for Basement Leak Near Chimney

Our Answer

Whenever we find a leak in a home, be it from a basement or roof, its natural to suspect the cause to be directly related to the area in which the leak is found. This however, is not always the case.

In your case, the basement leak could be caused by rain water saturating the chimney structure, falling to the bottom of the chimney and then dispersing across the basement floor. Any masonry structure like a wall or chimney is hydroscopic — meaning it soaks up a LOT of water, somethings masking the true source of the leak.

My suggestions would be to approach this by looking for the most obvious and common causes first, and those are defects in the gutter system or in the grading of soil outside the area of the leak.  Failures of roof and surface drainage are responsible for over 90% of all basement leaks and need to be eliminated first.  The details are covered in this post about the causes and cures for a wet basement.  Be sure to apply this advice to your entire home perimeter as I have frequently seen an issue like a leaking downspout cause a basement leak 20 or 30 feet away!

If that doesn’t stop the leak, I’d look at the chimney. Check for cracks in the chimney crown which is the mortar between the edge of the brick and the chimney clue.  If found, they need to be caulked (use silicone for that).  Also check the chimney flashing for leaks.  As a last resort, you can also apply a masonry sealer to the exterior of the brick chimney but make SURE is is “vapor permeable” meaning it will allow moisture in the brick to evaporate out.  If not, the moisture trapped in the brick can freeze, expand and deteriorate the chimney eventually leaking to a significant repair cost.

Hope this helps fix the basement leak. For more info, call your question in to our national radio show at 888-MONEY-PIT.  We take calls 24/7 and will call you back the next time we’re in the studio.