Below-ground dwellings pose IAQ challenges

Air pollution, mold spores, radon, volatile organic compounds (VOCs), and other contaminants are always a concern in the spaces where people live, learn and work. Air purifiers play an important role in keeping indoor air healthy. But when people live and work below ground, there is often an elevated need to use air purifiers.

Living and working underground increases occupants’ exposure to airborne mold spores and other toxic contaminants, including radon. And even if occupants are not living or working in the partially or fully underground spaces of a home or building, the air down there will rise up into the upper levels of the structure. Basement air can also be drawn up and into HVAC equipment.

Indoor spaces that are partially or fully below ground are known as “sub-grade.” One primary area of concern for sub-grade spaces is radon, which seeps into the sub-grade floors through cracks in the walls and foundations that also act as an entrance for various pests. In homes, sub-grade spaces are generally basements and crawlspaces (an area underneath the house that separates the bottom of the house from the ground). “Controlling the environment in a crawlspace is a simple concept: Keep it dry and free of soil gas,” says microbiologist Cassidy Kuchembecker in the July issue of Indoor Environment CONNECTIONS (www/ Easy to say, perhaps. Tougher to do. Because heat and humidity play such a central role in indoor air quality, regional climate differences require varying strategies for homeowners depending on where they live. Basements may not be the norm in Florida, but crawlspaces are.

Typically, a crawlspace is too small for a person to stand upright. But it is less expensive to build than a basement, and still gets the house off the ground to fight against termite infestations. The crawlspace also allows access to plumbing and ductwork. In fact, it usually offers better maintenance access than does a finished basement because the crawlspace can be accessed from outside.

In Florida, crawlspaces typically suffer from excessive moisture in the soil plus excessive humidity. Suggests Kuchembecker: Keep the area clean and either completely open or fully sealed, Install a vapor barrier on the earth floor, and consider a dehumidifier or exhaust fan. In the Southwest, though, sub-grade air quality is a substantially different challenge. In New Mexico, for example, houses usually do not have basements or even deep crawlspaces because of the hard clay earth. Crawlspace depth is only a foot or less. Few homes have vapor barriers so radon and microbial VOCs are the real threat. Experts suggests installing vapor barriers and even power vents.In areas of the country with mixed temperatures and humidity, which includes much of the rest of the United States, flooding is an issue, as well as generally moist soils and vapor barriers. Thus another set of conditions and air quality challenges.


Homes are not the only structures that are occupied sub-grade. Commercial buildings, schools and other dwellings are also built with sub-grade spaces.

When classrooms are sub-grade, mold is a common concern along with the other indoor contaminants that affect homes: radon, VOCs and other trapped indoor air pollution. For example, the United Independent School District in Laredo, Texas, has sub-grade classrooms at its Trautmann Elementary School. Earlier this year, the school district hired indoor air quality consultants to perform a detailed assessment of air quality in its sub-grade classrooms.

The consultants gathered data and provided recommendations on any microbial growth concerns in the classrooms. They collected samples and conducted analyses to assess the presence of sewer gases, VOCs, and other organic compounds. They also gathered samples of airborne particulate matter. The report noted that water is the limiting factor for mold growth, so inspectors looked closely for visible mold, excessive dirt and water-damaged building materials. The report noted the consensus of industrial hygienists and researchers regarding the evaluation of mold concentrations:

  • Mold concentrations in indoor air should be lower in quantity but of the same composition as outdoor air.
  • The significant elevation of a single mold species indoors relative to the outdoor air is a definite indicator of a problem.
  • Special attention must be paid to any amplified presence of disease-causing or other toxic molds.

The assessment at the Trautmann Elementary School also included a detailed analysis of VOCs, focusing on potential skin irritants. When the researchers examined outdoor fungal spore concentrations and compared them to indoor concentrations, they found similar spore types. This led them to conclude that outdoor air was probably the source of the indoor mold spores. They also found elevated VOC levels. Recommendations for the school included:

  • Further inspections for water intrusion failures.
  • Removal and replacement of water-stained ceiling tiles
  • A review of materials in classrooms and the kitchen for potential VOC sources.
  • HVAC adjustments to improve air circulation and increase fresh air intake
  • Cleaning rooms to reduce dust mite allergens found in the air
  • Inspection of waste water systems to determine sources of sewer odors, if necessary.

The IAQ assessment, performed by Terracon Consultants, Inc. in Laredo, Texas, provides an engaging view into the world of sub-grade air quality issues, especially in classrooms. Obviously, air purifiers could play an important role in alleviating the air quality issues in sub-grade classrooms such as those at Trautmann Elementary School. High-performance air purifiers such as the systems IQAir provides for schools can remove almost all of the mold spores in the air. But it is important to remember that only elimination of the growth-source for the mold – moisture – will eliminate future growth of the mold. Success requires a focused mold remediation effort. Once the mold is eliminated and the source is removed, the indoor air can be kept free from contaminants by using air purifiers.

The number one air cleaning solution for your home.

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