Crawl Space

Mold in Crawl Spaces

Mold in a crawl space usually does not create a health issue, but can if there is significant transfer of air containing mold spores into the living space. Also, if the underlying water issues are not resolved, it can cause increased humidity in the home that may lead to mold growth in other areas.

Common Causes & Prevention

There are many possible sources of water intrusion into crawl spaces that may lead to mold growth. Some of the more common causes are listed below.

  • Ground water evaporation
  • Pipe breaks/leaks
  • Condensation of humidity on cold surfaces
  • Water runoff from gutters, improper landscape grading, irrigation systems, etc.
  • High ground water tables
  • Heavy rains
  • Poor drainage

As you can see from the list above, some of these issues are more common in Indiana than some other places. With our clay soils, high water tables, high rainfall, and humid summer weather it takes planning and preparation to keep the water out.

Gutters and Downspout Issues

Gutters and downspouts dumping water against the foundation is one of the causes of water in the crawl space that we see most often. Your roof collects a huge amount of water, even in a small rain shower. If the gutters don’t carry it away from the home, it will often flood crawl spaces and basements.

The solution to this is an easy one. Ensure your gutters are clear and in good working order, and the downspouts are long enough to carry the water away from the foundation walls. Be wary of dumping it all into your mulch beds as they can act as basins holding the water against your home.

Improper Grading

When a new home is built, a hole is dug out to place the foundation, then the soil is filled back in around the foundation when it is complete. Over time, the soil begins to settle and sink down, which can cause the ground around the house to be lower than the surrounding area. This can cause water to roll back into the crawl space or basement.

There are two general approaches to dealing with water from improper grading. The first, re-grading, is the more permanent but more expensive option. The second approach, dealing with the water once it enters the foundation, can be a short term fix, but often postpones the issue until later.

Irrigation Systems

Irrigation systems that deposit water too close to the house or in mulch beds can cause the same problems as gutter issues above. The simplest solution is to shut the irrigation off, or move it farther away from the home.

Another issue with irrigation can arise when leaks develop in the system. Pipes can break when earth settles around the foundation, when the ground around the pipes freeze and thaw, or when water in the system freezes. Often, water from the leak will then travel back along the outside of the pipe and into the foundation.

If you have a drop in water pressure in your irrigation system, you should check thoroughly for leaks.

Probably A Resale Issue, Not a Health Issue

Mold in a crawl space is not as likely to have a significant effect on the air in your home as mold growing inside the house, especially in small to moderate quantities. When the amount of visible mold becomes widespread or heavy, the likelihood it will have some effect on the indoor air increases. Even then, it probably will not have serious health effects to an average, healthy person.

It is much more likely that crawl space mold will be an issue when you try to sell the home. Home inspectors are looking carefully at crawl spaces, and most buyers will be hesitant to buy a home with visible mold. It is usually beneficial to take care of these issue before listing the home for sale. The situation can be more stressful, and involve more people, if you wait until a buyer has a home inspection.


We have a treatment that is very effective at cleaning mold and the underlying staining from the wood in crawl spaces. The process takes less time than more labor intensive methods of remediation, so it is typically much more cost effective. The video below is from an attic treatment, but the process is the same for crawl spaces. You can see from the results, this is an effective cleaning method and a great way to protect the value of your home.


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