Technical Papers

The Effect of Ventilated Versus Encapsulated Crawl Spaces on Allergies

Tuesday, March 31st, 2015 by Bill Cowley

Mold allergies are a serious problem in the United States and across the world. The World Health Organization stated that sufficient epidemiological evidence is available to show that occupants of damp or moldy buildings are at an increased risk of respiratory symptoms, respiratory infections, and exacerbation of asthma. The old system of venting crawl spaces was thought to help alleviate the moisture problems in houses, however studies have found that the traditional venting system is allowing damp air from the crawl space to circulate through the home and could pose a serious health issue. The more modern approach to removing moisture from a crawl space is encapsulation. This process decreases the amount of moisture in the crawl space and therefore decreases the chance of a homeowner coming in contact with allergens from mold or pests.

In the United States, 27 million houses have a crawl space. Approximately twenty percent of houses being constructed today are built with a crawl space. Crawl spaces have been used, and are continuing to be used, because they are a less expensive alternative to a full basement and allow easy access to pipes, electric cables, and ventilation systems. In theory they are supposed to provide a defense between the house and the moist dirt underneath.

Due to their underground construction, crawl spaces are often damp and dark with less temperature variation than ground level structures. Crawl spaces that are vented in the traditional way offer the perfect environment for the growth of mold because the environment meets the four requirements for mold growth: available mold spores, available mold food, appropriate temperatures, and considerable moisture.  Take a look at some photos of moisture and mold in a crawl space from one of our customers in Oceanport, NJ.

The moisture in the crawl space is not only advantageous for the production of mold, it lures pests to the home. Cockroaches, rodents, and other nuisance pests gravitate toward water sources. Allergens are created by these pests. Cockroaches are known to exacerbate asthma problems in some people and there are those who are allergic to the dander of mice. In addition to allergens created by pest animals, pest animals have the capacity to bring hundreds of possible pathogens into the home.

In the past, builders and homeowners alike believed that the best way to reduce the moisture levels in the crawl space was to vent the moist air to the outside. Building codes dictated that builders place vents on opposite sides of the house. The theory behind this system was that the cross-breeze would take the damp air out of the crawl space and replace it with less moist air from the outside. Although this theory seemed plausible, there are a number of flaws with this design.

The first problem with the cross ventilation theory is that air generally moves up, not across. This kind of air movement is referred to as the stack effect. When there is moisture in a crawl space, the damp, mold-infested air, is drawn upward into the living area of the house, not outward through the vents. This means the mold spores come directly into contact with the people in the house. Airborne mold and mildew spores from damp crawl spaces are among the most common indoor air pollutants and allergens. It is believed that up to forty percent of the air on the first floor of a home comes from the crawl space. Some of the musty crawl space air may leave through windows or other uninsulated parts of the home, but much of it will continue to rise through the entire house until it is expelled through the attic.

Another problem with the ventilation systems that were built following the old building codes is that during the summer, humid air is drawn into the crawl space where it deposits moisture in the form of condensation. These small droplets of water stay in the space covering the insulation, piping, and other material in the crawl space. The small droplets of water attach themselves to these objects and are therefore unable to be vented out. In addition to moist air coming in the vents during the summer, mold spores that are prevalent in the air outside the crawl space will also travel through the vents and be deposited in the crawl space.

In the winter, there is a very different problem with the ventilation system. During the winter, cold air is brought into the crawl space through the vents. This air can be cold enough to freeze pipes and therefore can cause significant moisture problems if the pipes crack or burst.

In order to decrease the chance of mold and pathogens being in a home, eliminating moisture from the crawl space is imperative. Instead of trying to remove moisture from a crawl space through ventilation, building codes are beginning to change and accept that encapsulating the crawl spaces is a better way to keep moisture out. The theory behind encapsulation is to never have the moisture enter the crawl space in the first place.

Encapsulating is a relatively new process in which the crawl space is completely and permanently separated from the environment of the surrounding earth. A drainage matting system will be installed to enhance the moisture and vapor retardation. Next, the crawl space professional will adhere a thick durable material that is similar to a pool liner to the floor and walls of the crawl space. They will also seal any air leaks with caulk and foam. The 20 mil thick vinyl that is placed on the floor and walls is strong enough that some infrequently used items can safely be stored on top of it.

The theory behind encapsulation is actually very different than the theory behind a venting system. In a venting system you accept that there will be moisture in the crawl space and you attempt to remove it. With the encapsulation process you actually stop the moisture from ever getting into the crawl space area from the earth below. Excess moisture does not need to be removed from the crawl space because it never enters the crawl space.

When there is no excess moisture in the crawl space, you remove the ability for mold to grow as well as remove environmental conditions that are enticing for pests, making the air inside the house cleaner and healthier for its occupants.

Encapsulated crawl space