Friday, June 28th by Kristina McGovern
When the relative humidity in a basement is high, it can lead to mold and moisture damage.
If you're a homeowner, it's important to understand what relative humidity is, how it can affect your home, and what you can do to control the relative humidity in your basement or crawl space.
When we say the air feels damp, we’re talking about the humidity in the air. But really what we’re referring to is the relative humidity. The relative humidity is the amount of water vapor in the air compared to the maximum amount of water vapor the air is capable of holding at a given temperature and pressure.
Here's an infographic that explains basement and crawl space humidity:
If the relative humidity is 50%, this means the air is holding half the amount of water vapor it could hold. When there’s no water vapor in the air, the relative humidity is 0%.
According to the Environmental Protection Agency (EPA),
indoor humidity should be kept between 30-60% to decrease mold growth. When the indoor humidity level is higher than 60%, the air is too wet, and the home becomes a breeding ground for mold, pests, and rot.
For more facts about indoor relative humidity, read this article about
relative humidity, temperature, and dew point.
High relative humidity is common in vented crawl spaces, especially in humid climates like in the Southeast. But high relative humidity is also common in basements too.
Water: Water can seep through cracks in the foundation and around basement windows. Water can also come from inside the house from a leaking pipe, water heater, or washer.
Condensation: Moisture from the soil can seep through a concrete foundation. Moisture also evaporates from standing water caused by a leak. When warm air comes in contact with cold surfaces, such as basement walls, pipes, or ducts, this creates condensation.
Outside Air: Damp air from outside can get in through basement windows or crawl space vents.
Most damage in the basement or crawl space itself is obvious, such as mold, rot, wet insulation, wet drywall, and the list goes on. But humidity in the basement or crawl space affects the upstairs too.
Since air flows into the upper levels of your home from the basement or crawl space, it brings the humidity from down there with it.
A brief explanation of how the natural airflow in a house draws humidity (and mold and musty odors) upstairs:
As warm air rises in a home, it leaks out of the upper levels. New air must enter to replace the air that escaped. This creates a suction at the lower levels to draw in replacement air. This process is known as the “stack effect.” It creates airflow in your home from bottom to top. Air from the basement or crawl space is drawn upward into the first floor, and then to the second floor. Therefore, whatever is in your basement or crawl space air is in your house and affecting you and your family, whether you spend time down there or not. If there’s high humidity downstairs, there is higher humidity upstairs than there would be otherwise - and mold spores and damp odors.
If the relative humidity in your basement or crawl space is high, you need to first find the source of the water or moisture problem before deciding how to fix it. The steps taken to fix a damp basement or crawl space are similar.
Water seepage in the crawl space can usually be fixed by installing a sump pump and drainage system. Water evaporating from the ground or moisture coming through the vents can be solved by encapsulating the crawl space (aka closing the vents and covering the walls and ground with a vapor barrier). A dehumidifier can help control the humidity level and keep your crawl space dry and free of mold.
Water in the basement can be solved by fixing plumbing issues and installing a sump pump and drainage system. Cracks in the foundation should be repaired. Installing a dehumidifier can keep the humidity level under control and help prevent mold in the basement.
If you think it’s time you do something about your damp basement or crawl space, contact Basement Systems to find a waterproofer near you and to schedule a free on-site evaluation and estimate.
To ensure professional installation and superior service we carefully created an international network of over 350 trusted basement contractors.