Barrier to Entry

Annual Termite Control Issue - Annual Termite Control Issue

Controlling moisture in homes can discourage termite invaders. Here’s what you need to know about enclosing crawlspaces.

February 10, 2016

The first step to encapsulating a crawlspace is to seal all penetrations from the crawlspace to the home and from the outside into the crawlspace. This prevents humid air from infiltrating into these areas.

Because moisture in crawlspaces can cause serious problems such as termite and other pest infestations, there’s an opportunity for pest management professionals to generate new business by preventing excess moisture situations, according to Walker Mobley, sales manager for Sante Fe Dehumidifiers, Madison, Wis. “Pest control technicians on the job are in the right spot,” he said. “They’re down in the crawlspaces identifying problems.” As such it’s important for PCOs to educate their staff about the relationship between relative humidity, air temperature and dew point, and how that can affect the environments of crawlspaces and basements, he advised. And it’s equally important to educate customers about potential problems and advise them to act to reduce or eliminate moisture.

“That’s a good opportunity for PCOs because termites literally eat away at the structure of a home, and the average cost to homeowners to repair that damage can be as much as $3,000,” Mobley said.

“Crawlspaces are widely created in home construction today with approximately 250,000 new houses with crawlspaces built each year in the USA. It’s estimated that there’s a total of about 26 million of these homes in existence today,” he added.

During a recent PCT magazine webinar, participants heard Mobley discuss how moisture can create an attractive termite habitat and what they can do to help their customers eliminate these situations — and create new revenue streams.

SOURCES OF MOISTURE. Moisture in the crawlspace infiltrates through the walls and floors because of common building practices. “As a result of this infiltration, moisture levels can quickly elevate in the crawlspace. Once above 60 percent relative humidity, mold, mildew, bacteria and other biological allergens can grow, leading to musty odors and other issues in the home,” he said.

“Termites thrive on moldy wood in damp crawlspaces and they like wood with moisture content of typically 20 percent or more, but that varies in different parts of the country. You want to limit that to a wood moisture content from eight to 12 percent. You can use moisture meters to measure that,” he suggested.

Relative humidity, according to Mobley, is the amount of moisture in the air, compared to what the air could hold at a specific temperature. As air gets warmer, it’s able to hold more moisture. As air gets cooler, it loses this property.

HIGH HUMIDITY & DAMAGE. “High humidity can lead to structural damage in homes as well as possible health-related issues. It is important to remember that the air in the crawlspace will make its way into the rest of the home,” Mobley said. “This includes musty odors and allergens. A 60 percent relative humidity for 72 straight hours can create mold, mildew and fungus problems. At a relative humidity of 75 percent, wood floors will start to cup. Walls and ceilings will become stained. And at 85 percent relative humidity, wood starts to rot and paint begins to blister.”

Mobley added it’s important to understand how temperature impacts humidity. If the water vapor content stays the same and the temperature drops, the relative humidity increases. If the water vapor stays the same and the temperature rises, the relative humidity decreases. This is because colder air doesn’t require as much moisture to become as saturated as warmer air.

“Dew point, another concept to understand, is the ratio of moisture in the air at a specific temperature to the maximum amount the air can hold at that point,” he explained. Dew point is the temperature at which moisture condenses. Relative humidity is relative to the temperature, and dew point is the absolute. So the higher the dew point, the more moisture or water vapor is in the air, regardless of the temperature. If you have a dew point higher than the surface temperature, you get condensation. A dew point lower than the surface temperature results in no condensation.

Condensation contributes to: high humidity, pest infestations, poor indoor air quality, mold growth, musty odors and more.

REAL-WORLD EXAMPLE. Mobley cited a “real-world” example of this: “A can of soda taken out of the refrigerator in the summer will sweat. But it won’t sweat if it’s taken out of the fridge in the winter. The air inside a house, whether during summer or winter, is roughly the same temperature, within a few degrees. And the surface temperature of a can of soda is exactly the same the year around. So what’s changed? It’s the change in the dew point of the air that has leaked into the house. In the winter that dew point will be lower than the temperature of the can; in the summer it’ll be higher. That’s the same factor that causes condensation in crawlspaces.”

Dew points in some areas of the United States can be a real problem, he stated. “At certain times of the year, wet air in the Midwest, Northeast and Southeast triggers high dew points. Where there’s dry air, no dew point problems exist.”

Mobley explained that excess moisture found in houses is usually caused by imperfections in foundations, open foundation vents or diffusion through building materials. The more porous the building materials, the easier it is for water vapor to diffuse into the area. Excess moisture also can be internally generated by the residents.

“That moisture, of course, creates damaging wood rot, as well as the creation of spores,” he said.

FIXING THE PROBLEM. How can pest management professionals help their customers prevent or correct excess moisture?

“To fix that problem,” he said, “you should encapsulate (enclose) the crawlspace.” There are several basics to accomplish in doing this:

  • Seal the outside vents and the cracks in the foundation. You can do that with Styrofoam, caulk or similar materials.
  • Install a vapor barrier. It needs to be a professional-grade product, Mobley said, and should not be constructed from recyclable materials. The mil (thickness) should usually be rated 6, 8, 10, 12 or 20. This does two things: Higher vapor barriers lower the permeability rate, thereby allowing less moisture, and also create puncture resistance.
  • Install a dehumidifier. No matter how tightly you encapsulate a crawlspace, moisture will still come in. The dehumidifier will reduce the moisture and circulate the dry air to all parts of the crawlspace.
  • Line the walls of the crawlspace to help reduce moisture diffusing through those walls.
  • Always leave room for your inspection.
Air can leak into the home through walls, roofs and floors and have damaging effects on a house.

ENCAPSULATION PREP. “In preparing for the encapsulation process, always consider safety for those doing the job,” he said. “Be very cautious if there are combustion appliances such as a HVAC system or water heater located in the crawlspace. If there’s standing water in the space, it must be addressed before proceeding. Maybe a sump pump is needed or an improved gutter system, or possibly landscape grading.

“Use a high-quality waterproof tape for securing the liners to the foundation walls,” he added. “If you don’t do this it could come back to bite you.”

Most crawlspaces will need a high-quality dual-exhaust dehumidifier in order to maintain a relative humidity level of 60 percent or lower in a crawlspace. Mobley suggested placing it as close to the center of the crawlspace as possible. “That’s to be done to allow for maximum air circulation. If you can’t do that, at least allow for a minimum of 1 foot around on all sides. You want to make sure you’re getting dry air on all corners of the crawlspace.

“If you do this correctly, you’re creating a less hospitable environment for those damaging termites, dust mites, centipedes, silverfish, spiders and other unwanted pests. There are also several additional benefits to the homeowner, such as improved indoor air quality, comfort and property protection.”

The author has been writing about the pest management industry for more than 30 years. Email him at