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Answers To The Top 3 Questions About Crawl Space Humidity

By Chuck Henrichsen on May 23, 2014

Homeowners want to know where to start. We spend a lot of time talking about the dangers of moisture in your crawl space, but what should be your next step? The answers to these top three questions that homeowners ask give practical recommendations to maintaining your crawl space and avoiding moisture damage and mold.



“What’s the threshold humidity level for mold growth?”

When the relative humidity of your crawl space is 70% or higher, mold can thrive. “Relative” humidity is the humidity level expressed in a percentage of the amount of moisture in the air needed for “saturation” (i.e. the highest level of humidity - 100%). The amount of water the air can hold (humidity level) is dependent upon the temperature of the air itself. Colder temperatures are able to hold less moisture. Homeowners should be wary of the condition of their crawl space when the humidity level begins to creep up past 70% relative humidity.

“I’m seeing condensation. What does that mean?”

Condensation is an indication that the air within your crawl space has reached 100%. The air can no longer hold the moisture and it’s condensing onto the surfaces in the vicinity. This causes the organic materials that make up your crawl space to become damp, inviting toxic mold to set up shop.

“How do I know when the humidity in my crawl space is at a dangerous level?”

A hygrometer is a device used to measure the humidity of indoor air. Using this tool to measure the humidity of your crawl space is a great way to monitor the amount of moisture present. These devices can be purchased for a small cost—as little as ten bucks. Rest assured that everything is hunky-dory when the humidity level is below 70%. However, as soon as it approaches 70%, it’s time to break out the dehumidifier.

A thermo-hygrometer measures both temperature and humidity level. These devices are even more ideal for crawl space atmosphere monitoring because the relative humidity level is contingent upon the moisture in the air in relation to the air’s temperature. Being able to track the changes in both of these conditions in your crawl space will allow you to see trends and anticipate necessary changes.

For instance, if the weather is hot during the day but the temperature plummets at night, this can cause problems for your crawl space’s humidity levels. The daytime temperature is higher, which allows the air to hold more moisture. As night approaches and the air cools, the amount of moisture the air can hold also decreases - causing the relative humidity level to rise. A crawl space that was at a permissible humidity level during the day can run into problems when night falls. Being able to see these changes on your thermo-hygrometer can help you identify these types of trends so that you can respond appropriately.

Keep in mind that properly insulating your crawl space and installing vapor barriers will help regulate the temperature and keep moisture levels down, resulting in less fluctuations in the air’s relative humidity.

Your Next Step Should Be...

We would suggest that you purchase a hygrometer or a thermo-hygrometer in order to ensure that your crawl space’s humidity is at a safe level. If your crawl space is already obviously damp, is lacking an adequate vapor barrier, or is poorly insulated, it would be wise to address those issues as soon as possible.

For information about crawl space cleanout, insulation, or vapor barriers, contact Clean Crawls. We’ve been thrilled to work with an array of homeowners to provide them with a clean crawl space and healthy air quality.

Chuck Henrichsen

President and CEO of Clean Crawls, Treasurer of E3 World Wide, proud husband and father.

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