What can you do to prevent mold under your house?

Crawl space mold can be the some of the most difficult and expensive of all the mold removal projects, mainly because of the space restrictions - not the mention the time and expertise it takes to properly remove mold from the crawl space walls, floors, joists, etc.

To make matters even worse, crawl spaces are incredibly common places in the house to find mold, because moisture builds up quickly, and often goes unnoticed by the homeowner because very little time is spent in the crawl space. If you want to prevent mold under house and avoid a costly removal project, keep these tips and tricks in mind.

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Why are crawl spaces prone to mold?

Crawl spaces are prone to mold growth because of the high moisture and humidity levels that are often associated with those spaces. So why is moisture so prevalent in crawl spaces and how can you prevent mold under house?

It's pretty simple logic, actually. Your crawl space sits underneath your house, right on top of the dirt, soil, and other earth that acts as your house's foundation. Soil and dirt and everything else that comes from the earth all contain moisture. Moisture is one of two ingredients needed for mold growth, and because moisture is created so easily in narrowed areas, dirt crawl spaces are natural breeding grounds for mold.

While moisture from dirt and soil will normally evaporate into the atmosphere, it can easily get trapped in a closed-off, unvented area like your crawl space. When moisture is not properly vented outside, it will begin to condense on your crawl space's foundation walls and subflooring.

What can be done to prevent mold under house?

  • To prevent mold under house, first check your crawl space's foundation walls to make sure there are no cracks or leaks.
  • Also look for holes and cracks in your crawl space ceiling.
  • Consider your gutters and downspouts, and check to see if they are channeled away from the house.
  • Check for sufficient ventilation.
  • Make sure that if you have a vented crawl space, you insulate tightly against the subflooring.
  • Check for leaks around plumbing apparatuses and HVAC ducts.
  • Be sure your dryer vent is vented to the outside of your house instead of into the crawl space.

What are the most common solutions to prevent mold under house?

The three most common solutions to prevent mold under house include:

  • Crawl space vapor barriers
  • Dehumidifiers
  • Crawl space ventilation systems

Moisture Control

If you find moisture during a house mold inspection, Advanced Energy recommends adding interior and exterior drains for the crawlspace. Crawlspace drains should be separate from the foundation drains. Industry professional, Mike Trotter says, "Good exterior drainage is the first requirement of a crawlspace system."

Vapor Barriers/Liners 

Once you've controlled the moisture issues, close the vents, and add a vapor barrier to the ground and the walls. The Advanced Energy research shows the minimum thickness required to stop the moisture is a 6 mil polyethylene liner.


It is good practice to place a meter in the crawlspace that will monitor the relative humidity. Relative humidity should be kept below 70%, yet not too dry. Advanced Energy's researcher Bruce Davis says they have run into problems where the relative humidity under the house is actually too dry. "You can over dry a crawlspace," he says. "If the wood moisture content is drawn down from 60% to 5% you will definitely see shrinkage and cracks in the floor. That is an extreme difference in relative humidity."

Ventilation, Ventilation, Ventilation

According to another Advanced Energy study, implementing additional ventilation to increase crawl space air circulation actually causes higher relative humidity levels, as well as ways for energy to escape. Plus, it exposes your home and invites pests from the outdoor environment into your crawl space.

The Advanced Energy field study shows consistent evidence that insulated crawlspaces outperformed ventilated crawlspaces. Here are the most important findings from the study on crawlspace moisture problems:

In sealed crawl spaces, wood moisture threshold stayed below 12% - which reduces the potential for mold growth and termite infestation affecting lumber framing.

Insulated crawlspaces were also dryer than traditional wall-vented crawlspaces: The daily average relative humidity level stayed below 70%.

When tested in a dryer climate, the sealed crawl spaces controlled normal moisture levels (around 50%); yet the vented crawl spaces kept 70% relative humidity for a only a few days.

Impressive Energy Savings: Homes with sealed crawl spaces and insulated floors saved about 20% in natural gas during the winter, and an added 15% annual energy savings compared to the control group.

More info? For more information about common places for moisture in your home, check out our related post: Crawlspace Moisture Problems.

Don't wait until it's too late! If you suspect or see mold in your home or business take action today.

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