The majority of people feel that outdoor air is healthier than inside air. "It's stuffy in here," we say. "Get some fresh air by going outside."

It would seem sensible, then, to air out your crawl space. It's rather damp down there, so letting some air in should help. And, because you're never going to go down there, you may as well air it out all the time. Is the issue resolved? Not quite. Venting a crawl space might worsen the situation.

Relative Humidity

When we talk about "relative humidity," we mean how wet the air is in comparison to the maximum quantity of water it can contain at a particular temperature.

Consider this example of what occurs on a hot day. Your vents are receiving 84°F air with a relative humidity of 75%. Your crawl space's air temperature is 66°F, while the surface temperature of the walls, soil, and floor joists is 62°F. What will happen when this air comes in? Will it get rid of the damp air in the crawl space and make things better?

Because cold air holds less water than warm air, cooling the air by one degree raises the relative humidity by 2.2%. Looking at our warm weather scenario, there is a 22°F difference between the 84°F outside air we are letting in and the 62°F crawl space surfaces. Simply multiplying 22°F by 2.2% results in a 48% rise in relative humidity where it hits the surfaces.

Our 84°F air began with a relative humidity of 75%, meaning it was 75% full of water. We have now cooled it to 62°F, thus the relative humidity increased by 48.4%. This would result in a relative humidity of 123.4%. But wait, we can't have more than 100% relative humidity. So why not? Because the air can no longer retain any more water and must release it.

What exactly do we mean by "give up its moisture?" We imply that it will either rain or settle as condensation on surfaces. The dew point is the point at which air gives up its moisture when the relative humidity hits 100%.

When this warm, humid air enters a crawl space, it would literally rain if the crawl space air was cooler than the crawl space surfaces. However, this is never the case. The source of the warmth is the air flowing in from the vents, therefore the surfaces in your crawl space are always cooler than the air in your crawl space.

So on this hot day, we get condensation, which means our crawl space gets wet. The floor's dirt surface becomes damp. Our air ducts become damp, especially if we have air conditioning on, which causes the ducts to become chilly. Our cold-water pipes become soaked. These are the coldest surfaces. Condensation gets on our floor joists, girders, still plates, and insulation. Wet insulation becomes heavy and falls to the crawl space floor.

When there is high humidity in a crawl space, all porous materials absorb moisture from the air like a sponge. The relative humidity and moisture content of wood have a direct relationship. In a moist atmosphere, wood will grow damp.

Mold grows on damp wood and causes it to decay. All of these wet surfaces must ultimately dry, and the moisture must go somewhere. Assume we had a couple hot summer days that resulted in moisture in the crawl space. Then the following four or five days are colder and pleasant. Is the issue resolved? No way. After a hot day, we had wet crawl space surfaces all over the place. They dry into the crawl space air over the next several weeks and months, while mold and wood-destroying fungus feast on your home.

The Solution - CleanSpace Encapsulation

To protect the integrity of the wood supporting the floor from crawl space humidity, we recommend the CleanSpace Encapsulation System, transforming the crawl space into a moisture-controlled and conditioned space. The CleanSpace Encapsulation System covers all bases in terms of moisture in the crawl space.

Many crawl spaces we inspect have pools of water collected from groundwater & condensation. CleanSpace Encapsulation seals out both groundwater and humid air, covering both fronts. But it isn’t enough just to have a vapor barrier covering the ground.

Water unable to enter the crawl space will still collect under the vapor barrier. With common unsealed vapor barriers, moisture collects under the liner until saturated and enters the crawlspace anyway around the unsealed edges of the vapor barrier. But once the moisture is sealed out with a CleanSpace Vapor Barrier, there also needs to be proper drainage underneath. As a part of the CleanSpace Encapsulation System, a layer of drainage matting, and a perimeter drainage system are used to lead the water to a powerful sump pump. Then, the water can be pumped out and away from the home.

Encapsulation seals off outside humid air but also includes the installation of Foamax wall insulation and spray foam insulation to seal off as much of the outside air leaks as possible. A SaniDry Sedona Dehumidifier, one of the most powerful and energy efficient dehumidifiers on the market, is installed to monitor and control the relative humidity level in the crawl space to a safe 55%, preventing mold growth and wood rot.

Anyone who owns a home with a dirt crawl space should consider having it encapsulated to help preserve the value of the home. In the coastal GA & SC area, having an unsealed dirt crawl space without a moisture problem is unheard of.

We offer free inspections to inform homeowners of the full extent of the issue and provide written solutions customized to the needs of the home.

Click here to schedule a free inspection.