When basements aren’t practical due to the composition of the ground, home builders create crawl spaces instead. A crawl space is an area between the earth and the floor joists. This is typically an unfinished area with a height between 18 and 36 inches.

Home designs often use the crawl space for convenient access to electrical wiring, plumbing, and HVAC equipment. However, the primary purpose of crawl spaces is moisture control. The moisture and heat in a crawl space can undermine home comfort, energy efficiency, and indoor air quality. Ventilation and encapsulation are two prevalent approaches to lowering moisture in crawl spaces.

Moisture Problems in Crawl Spaces

Crawl spaces were once the most common way to build homes in warmer climates throughout the United States. While they’re still built, crawl spaces are becoming less common, and moisture is among the top reasons. Crawl spaces are in direct contact with the earth, which is naturally moist. They’re also prone to excess dampness due to foundation and landscape drainage issues. A humid crawl space is an ideal setting for mildew, mold, and pests. Also, floor joists can rot over time and require major repairs.

Air from a crawl space even gets into the home through the stack effect. This is a phenomenon whereby temperature differences between the home and crawl space create a vacuum. That vacuum draws air from the crawl space into the living spaces. By doing so, it can introduce air pollution, undermine cooling and heating, and cause your energy bills to rise.

Building Codes and Permits

Local residential building codes often govern crawl space requirements. Your crawl space had to meet the codes when the builder constructed the house. Any significant changes to a crawl space will usually require a permit. That has a couple of implications. The first is that your technician must adhere to current codes with any changes made. The second is that a city inspector must approve the changes after your technician completes the work. This is why it’s important to consult with a crawl space specialist as early as possible in the process.

Passive Crawl Space Ventilation

Most crawl spaces require some form of ventilation, which helps to normalize the air in the crawl space with the ambient air. The other benefit is air movement, which reduces humidity in the space. It does this by drying moisture on surfaces and introducing drier air that helps balance out the levels. Passive ventilation is the traditional and most basic approach. Many crawl spaces have small, rectangular vents along the home’s foundation. When opened, these vents allow for an exchange of air between the crawl space and the outside air.

Many homeowners ask whether passive ventilation is enough, and the answer is, “It depends.” In relatively dry climates, passive ventilation may be enough. In humid climates, passive ventilation typically doesn’t provide enough airflow. In any climate, passive ventilation can be unreliable. Factors that undermine performance include vent blockages, strong winds, and heavy rains.

Mechanical Crawl Space Ventilation

Mechanical ventilation systems are superior in several ways. They can move much more air from outside the home into the crawl space. Wind and other weather conditions don’t affect the performance of a mechanical ventilator. While blockages are still a concern, obstructions don’t occur as easily with mechanical systems as they do with passive vents. The most common crawl space fans are like the exhaust systems used in kitchens and bathrooms.

Whether it’s mechanical or passive, there are limitations to ventilation. Moisture removal can occur only if the outside air has less moisture in it than the crawl space air. This will usually be the case. Still, in humid climates, such as the Southeast U.S., the difference can be small. Some dehumidification will occur but perhaps not enough to offset excess moisture in the crawl space and the stack effect.

Crawl Space Encapsulation

Encapsulation involves sealing a crawl space’s floor and walls. A vapor barrier is what creates the seal. This barrier comprises multiple layers of thick, heavy-duty polyethylene plastic. That plastic prevents moisture and pests from entering the space. When moisture is blocked, the crawl space is much less prone to mildew, mold, and rot. The barrier not only stops insects but also bars larger pests, such as mice and rats.

Encapsulated crawl spaces generally require ventilation, too. Most building codes require it, and it’s recommended even in cases where the code doesn’t. Passive ventilation usually isn’t viable because it undermines the encapsulation. In drier climates, a crawl space fan may provide the needed ventilation. In most climates, it’s necessary to install a dehumidifier.

Dehumidification

The ideal relative humidity (RH) in a crawl space is between 45% and 55%. Achieving less than 55% RH through passive or mechanical ventilation alone can be difficult in humid climates. A vapor barrier will block excess moisture but may not keep the RH at a lower level than the ambient air. The solution is a crawl space dehumidifier. This device has a blower that generally provides all the ventilation a crawl space needs. It also actively lowers the RH.

Some dehumidifiers have a desiccant material that absorbs moisture as air flows over it. More advanced systems use a refrigeration process much like that of an air conditioner. Air flows over a coil that causes condensation. That condensation then drains out of the crawl space via a pipe.

Foundation and Landscape Drainage

Crawl space encapsulation and ventilation are often enough when ambient humidity is the only concern. Yet moisture can get into a crawl space in other ways. These can include improper drainage of the foundation, landscape, and hardscapes. It’s often important to have a well-functioning gutter system that channels rainwater away from the foundation. Landscaping adjustments may be necessary if the lay of the land channels water into the crawl space. For some properties, homeowners may need to install French drains and other drainage solutions.

Crawl Space Inspection Services

If you’re concerned that your crawl space may need upgraded ventilation and perhaps encapsulation, schedule an inspection. A crawl space specialist will perform a comprehensive inspection and provide you with a professional assessment. Your technician can let you know if your crawl space isn’t up to code and what’s required to get it there. You’ll also be able to explore the various solutions, such as adding drainage, ventilation, encapsulation, dehumidification, and so forth.

Crawl Space Ventilation and Encapsulation in Greater Charlotte

RhinoLift Foundation Solutions has locations in Charlotte and Cornelius, NC and serves the surrounding areas. Our team offers a full range of geotechnical services for residential and commercial clients. We perform all manner of concrete repair and leveling for driveways, sidewalks, and patios. Our experts repair foundations and retaining walls and install foundation drainage. We also repair leaning chimneys and perform push piers service, helical piers service, and deep soil foam injections.

Our company also offers many basement-related services, including waterproofing, drainage installation, wall repair, wall anchoring and carbon fiber reinforcement, and dehumidification. For crawl spaces, you can count on us for repairs, drainage, dehumidification, ventilation, and encapsulation.

To learn more about these services or to schedule an on-site consultation, get in touch with RhinoLift Foundation Solutions today.

Meet the Author
Ashley Herrera
Ashley Herrera

Marketing Manager

Ashley Herrera is a seasoned expert in the foundation repair industry and strives to educate homeowners on the importance of foundation health.
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