Relative Humidity and Your Vented Crawl Space
SaniDry CSB Crawl Space Dehumidifier
SmartSump Sump Pump System
CleanSpace ® Crawl Space Liner
Here in southeast and low country areas, most houses with dirt crawl spaces are vented. Years ago, it was rationalized that since the ground naturally has a lot of moisture, installing crawl space vents would allow the moisture to flow out through the vents. However, venting does not make sense, unless the outdoor air is 70-degrees and 45% relative humidity day and night.
Let's take a look at where high humidity comes from, and what to do to control it.
Air moves water in and out of spaces and brings its moisture content with it wherever it goes. When air is heated or cooled, its relative humidity changes. The relative humidity of air goes down by 2.2% for every degree we heat it and up by 2.2% for every degree we cool it. Relative humidity is the amount of moisture in the air compared to what the air can Âhold at that temperature.
"Water does very little to ruin a home with a dirt crawl space. It is the water vapor that kills the house." ÂLawrence Janesky
Since crawl spaces are naturally cool, when warm humid air is brought into the crawl space, the air is cooled, and the relative humidity goes up.
Let'Âs say you have 84-degree air with 75% relative humidity entering your vents. Your crawl space is 66degrees, but the surface temperature of your walls, dirt floor and floor joists are 62-degrees. What will happen when this air comes in? The air temperature is cooled by 22-degrees. Multiply this by 2.2% and we have a 48.4% increase in relative humidity. That equals 123.4% relative humidity! When the relative humidity reaches 100% and the air can not Âhold all the moisture, this is called the dew point.
High relative crawl space humidity in Beaufort, SC and surrounding Georgia areas can lead to condensation on the HVAC ducts, pipes and cold surfaces. As the crawl space insulation in Savannah gets saturated with condensation, it gets heavy and falls down to the crawl space floor. Porous materials in a damp environment soak up moisture from the air like a sponge, and can result in wood rot and mold growth.
Now that you know where high humidity comes from, let'Âs look at options to control it.
We know that venting the crawl space does not work to get rid of dampness, it just increases it. Instead, we need to seal the vents and other outside air leaks and install a dehumidifier with air filtration, such as the SaniDry
CSB which is constructed specifically for crawl space environments. This unit will ensure that the relative humidity stays below 55% all year long so mold does not have a chance to grow.
But wait! Sealing the vents and installing a dehumidifier alone will not solve your moisture issues. Remember, the ground is naturally damp, and contributes a lot of water vapor into the crawl space air. Not to mention some crawl spaces leak or even flood when it rains.
First you must fix any groundwater leakage. This can be accomplished by installing either a SmartSump or TripleSafe sump pump system. These are high quality, reliable pumps designed for crawl spaces. They also come with an alarm system to alert you of any potential problem. Next, to prevent moisture from the ground affecting your home, you must isolate the house from the earth. This step is the key to solving your dirt crawl space problem and can be achieved by using a 20-mil thick plastic liner, such as CleanSpace ®. The liner is fitted to your crawl space floor and walls to stop water vapor, while allowing for drainage to a sump if needed.
Now all crawl space solutions are not created equal, and may not be a solution at all. There are a few criteria to deciding which approach to use. The solution must:
- Stop water vapor from flowing up from the soil
- Stop water vapor from flowing through or off of the crawl space walls
- Allow water to drain from the walls to the sump locations
- Allow water to drain from the floor to the sump location
- Not get ruined when someone crawls on it
- Be durable, so it lasts as long as the house does
- Be affordable
"ÂA vented dirt crawl space raises your heating and cooling cost 15% (to 25%) every month, and makes it very likely you wiÂll have a big expense for mold removal and/or rotted wood replacement." ÂLawrence Janesky
The CleanSpace ® Crawl Space Encapsulation System ® satisfies all of the repair criteria and transforms your crawl space into a healthy, useable space.
Lowcountry Basement Systems is a member of the Basement Systems, Inc. and Foundation Supportworks Dealer Network. Information in this article is contained in Crawl Space Science by Lawrence Janesky. To schedule a free crawl space evaluation and receive a free copy of this book, please contact Lowcountry Basement at 1-800-638-7048 or visit www. LowcountryBasement.com
