It came from the crawl space…

Oct 18, 2019

Recently I have been getting a number of assignments that involve issues with a crawl space.  These projects are interesting because they’re not always easy to figure out; add to that the fact that you just never know what you are going to find in this dark and creepy area!  Let’s take a look at what could go wrong.

Moisture and Mold, Oh My!

Crawl spaces are typically below grade, and any time you have a hole in the ground, there is the potential for water to come in. Concrete walls are actually quite porous and with enough water pressure on the opposite side, there is the potential for leaks.  This water can attract a number of nasty things such as small wildlife and insects, however, the biggest air quality issue is mold. Clients often think that a little mold down there won’t be an issue because let’s face it: who lives in their crawl space?  Regardless, wet crawl spaces can have a huge impact on a residence’s air quality.

Drainage, Grading, and Dry Crawl Spaces

Exterior drainage systems can go a long way to properly steer liquid water away from your property.  An even cheaper method would be to slope the exterior ground away from the foundation. One of the best ways to keep the crawl dry is to make sure water never gets in in the first place. A sump pit at the lowest part of the crawl can also help if water still manages to get in.  With no moisture, it is very difficult for mold to grow.

High Humidity and Condensation in the Crawl

Problems are not just limited to liquid water, humidity can also wreak havoc. Humidity from the crawlspace can impact the home above and can lead to condensation on any uninsulated supply ductwork or pipes. What could go wrong with condensation?  The answer is again, mold. Mold needs moisture and condensation can give mold the fighting chance to survive.  

Ventilation and Dehumidifiers

When dealing with elevated relative humidity, we first have to see if the crawl space is vented or unvented.  A vented crawl would be considered a part of the outdoors and under certain conditions, it can prevent condensation problems.  Alternatively, a sealed-off crawl space is considered part of the living space of the home and requires a dehumidifier. The worst possible combination is a sealed up crawl space with dehumidification. Be sure to carefully monitor the humidity levels to ensure they don’t exceed 60%.  

What’s That Smell In the Crawl Space?

Odors can come from a wide variety of sources in a crawl.  Moisture and mold can have their own “musty” type of odor, which can be an indication of a problem. Can odors come from other sources? Yes, odors can emanate from the soil if your crawl space has a dirt floor.  Sometimes clients store a wide variety of chemicals such as cleaning supplies, paint cans, stains, and pesticides that can off-gas into the air. During the summer, a hot crawl space can activate these odors, which can diffuse throughout the home.  Small leaks in return ductwork passing through the crawl can suck these odors in and send them throughout the entire house.   

Enclosed Spaces, Vapor Barriers, and Radon Systems 

In addition to removing items like paint and pesticides, crawlspaces can benefit from vapor barriers to cut down on moisture and odors from the ground.  An upgrade for a sealed crawl space would be to install a radon mitigation system to send humidity and noxious odors to the outdoors before they ever have a chance to get in your crawlspace. The added benefit to this system is that if there is an elevated level of radon in your home, the system will safely send this dangerous gas to the ambient air outdoors. 

Crawl Spaces and Dead Animals!

No discussion would be complete without some of the weird things that I can find in this dark and dank part of the building.  In addition to my encounters with spiders, insects, mice, and skeletons of unknown origin, I would also have to include my experience of crawling past a dead cat.  Yes, dead animals can be an issue; when fresh, they attract vermin and flies and can have an effect on indoor air quality. 


When it comes to indoor air quality, crawl spaces are always a “go-to” area for me to investigate.  They often hold the dark secrets of mold and odor problems. A professional can help you properly diagnose any issues and bring you some peace of mind.