Humidity And Your Crawl Space

Tuesday, April 25th, 2017 by Brian Bigger


You may think that your crawl space is in good order. After all, when it rains, you don’t have puddles in the crawl space. Also, you may have vents to help keep air moving through the crawl space and keep it dry. There are no plumbing leaks. This crawl space is an architectural masterpiece.

Well, there’s a problem. Protection against rainwater alone is protection against the dangers you can see but ignores another potential danger that is not so obvious: humidity levels (water vapors in the air).

Relative humidity in essence describes the air’s moisture content in terms of a percentage of what moisture the air is able to hold at that temperature. Why is this important? When temperatures change, humidity levels change along with it. When humidity levels reach their maximum, it results either in precipitation or condensation. Consider a sunny day when warm humid air enters a cool crawl space. The warm air is cooled, causing the air’s relative humidity to rise, (because cooler air can’t hold as much moisture). The next thing you know, that air now can’t hold all of it’s moisture and condensation begins to build up on the block wall and floor joists. Over time this leads to sagging and/or rotting joists, mold, and a litany of other potential problems.

Let’s look at an even more specific example. This summer as we have rising temperatures, imagine a day where we reach 82 degrees with 68% humidity. Now consider that this air enters the vents of the crawl space where it’s 64 degrees. Humidity levels will rise 2.2% for every degree that the air is cooled, with this air being cooled 18 degrees. 2.2 x 18 = 39.6 That means a 39.6% rise in relative humidity. 68 + 39.6 = 107.6% humidity. You’re looking at that saying, well you can’t have over 100% relative humidity in the air, so what happens? The moisture settles on the various surfaces in the crawl space and wreaks havoc. This plays out continually all summer long.

This leads to another good point. The idea behind having multiple vents in a crawl space is that air will enter through one vent and exit out another keeping air moving and preventing moisture in the crawl space. This is a fallacy. The airflow actually creates what is called the stack effect. It enters through all the vents and then works its way up into the home and out the upper floors. So effectively, warm air flows into the crawl space and is cooled, depositing moisture all the while. As mold begins to grow in the moist environment below the home, mold spores are carried upward into the home and you end up breathing that air. You may even notice a moldy smell in your living areas.

The best defense against humidity in your crawl space is encapsulation and a dehumidifier. Encapsulating the crawl space with our CleanSpace vapor barrier on the floor and walls as well as putting airtight covers on vents and doors will completely close off your crawl space from the outside. You now have ultimate control of the space. A dehumidifier helps to remove any water vapors from the air and keep everything dry and safe.

If encapsulation of your crawl space is something that you’d like to do to safeguard your home from mold and rot, give us a call to schedule a free estimate.

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