Trying To Find The Source Of A Basement Water Leak Before You Waterproof? Check The Chimney

A leaking basement is certainly no fun, but finding the source of the leak can be harder than actually fixing it. If your basement is leaking but you don't see an obvious source of the problem you may be overlooking a common source of basement leaks: your chimney and fireplace. This is what you should know.   

Water can find its way from the ash pit into the basement.

Underneath your fireplace is a space called the ash dump, which leads to a metal sheath that's known as the ash pit. That makes it easy to dump the ashes out of the fireplace so that they can be removed through the cleanout door. In some houses, the cleanout doors are located outside, just above the foundation. In other houses, the cleanout door is located in the basement. In some fireplaces, the ash dump has been closed off over the years during renovations, so you may not even be aware of its existence—especially if the close off occurred prior to your ownership of the house.  

If you don't regularly use your fireplace or aren't aware of the ash dump, this can easily become an overlooked source of water, especially if the chimney falls into disrepair. The ash pit is not usually waterproof, which means that if water is leaking into your chimney when it rains or snows, water will get into the ash pit and leak into your basement.

There are several possible sources of leakage.

In order to see if water is leaking into your chimney, consider having an inspection done. There could be a number of issues that lead to a leak whenever it rains:

  • The chimney cap may be missing or cracked. That's a common development, especially after bad storms. 
  • The crown of the chimney could be leaking or damaged. If your chimney was built before the mid-1980s, it may lack the reinforced rebar and angled top that helps it shed water. If your chimney has deteriorated, gaps may have opened up around the flues, letting rain and snow in.
  • The roof flashing around the chimney could be pulled loose or cracked. Flashing should be sealed with a single line of caulk, to prevent small leaks from getting through.
  • The gutter system could be overflowing, forcing water into the chimney, especially if there are visible cracks in the mortar.

To test the issue, you may need a chimney repair company to inspect the chimney and ash pit for signs of water damage or limescale residue. If this is the issue, you'll have to get the necessary repairs done to the chimney or roof before you can resolve the issue with the basement.   

Once you identify the source of your leak and get it stopped, consider getting the basement waterproofed (by professionals such as Paul's Basement Waterproofing). That will seal off your basement from any further sources of water damage. 


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