Prevent Mold Growth—and Fear—at Your Site

Prevent Mold Growth—and Fear—at Your Site

The headlines are alarming. It has become all too common to see reports about “toxic mold” shutting down buildings, or about families fleeing from “black mold” in their homes. These types of stories have fueled public hysteria leading to skyrocketing mold-related lawsuits over the past decade.

The headlines are alarming. It has become all too common to see reports about “toxic mold” shutting down buildings, or about families fleeing from “black mold” in their homes. These types of stories have fueled public hysteria leading to skyrocketing mold-related lawsuits over the past decade.

Much of what has been published about mold in the general media and on Internet sites is misleading and, at times, exaggerated. Two terms that are frequently mentioned—“toxic mold” and “black mold”—are not scientific or technical terms, says Daniel Tranter, a research scientist with the Indoor Air Unit of the Minnesota Department of Health.

“Those terms have been coined by the media and by people on the Internet,” he says. “A common misconception about mold is that scientists have concluded that there is a certain type or types of mold that are especially harmful to the population. We have not found reason to differentiate between certain types of mold or treat them differently than other types of molds.”

Many of the misunderstandings surrounding mold are about the health effects, says occupational and environmental medicine (OEM) specialist Hung K. Cheung, MD. Cheung is a former Maryland State medical director, and president of Dr. Cheung/OEM Advisor, LLC.

“It's not that mold never has a health impact; rather, the health claims explosion and public worry far exceed either provable or likely illnesses,” he stated in a testimony on mold to the Florida legislature. “The misperceptions of mold hazards are often a more important solution driver than the risks themselves. These fears can be very expensive and may lead to evacuations, building material deterioration, property damage, breaking of leases, and lawsuits or other legal claims. They can also be, and often are, exacerbated by thoughtless or unknowledgeable ‘professionals.’”

While there is not enough research to support the hype about toxic and black mold, both Cheung and Tranter agree that there is sufficient evidence that mold growth in buildings can have adverse health effects on those who are sensitive to it. “We know that allergy, respiratory, and asthma symptoms can be triggered by mold,” says Tranter. “Beyond that, we don't know much about the potential health effects. We consider all molds to be a potential health hazard, which should be dealt with properly.”

Common Causes of Mold in Residential Buildings

What causes mold growth in residential buildings? Moisture is the main culprit. “Mold needs a variety of environmental conditions to grow, such as the right temperature range, mold spores, and organic matter that the mold can eat, like paper on drywall, dust that collects on surfaces or on carpeting, or other organic matter, like chipboard,” Tranter explains. “Moisture is the one that is easiest to control and manage.”

Mold growth is a symptom of moisture intrusion, agrees Cheung. “Mold is everywhere. Managing it is a matter of determining where it is coming from, whether it is amplifying, and locating the water source,” he says. “Getting rid of the mold is not the cure-all—it's eliminating the water source so that you don't get it again.”

Potential sources of moisture in residential buildings include:

  • Leaking pipes, windows, and roofs;

  • Inadequate ventilation;

  • Inadequate air conditioning;

  • Improper drying of flooded areas;

  • Overpopulating a residence;

  • Keeping a unit closed up without running A/C or a dehumidifier;

  • Multiple indoor houseplants; and

  • Poor housekeeping habits.

Proactive Mold Prevention Practices

Sites can take a proactive approach to mold prevention by conducting routine property inspections. Tranter recommends checking all areas that have water usage (that is, plumbing), making sure that the roof is maintained and in good condition, checking the below-grade areas to see if there has been any water intrusion, especially after heavy rainfall or after early spring rains when the ground is still frozen.

Also, check the exterior of the property for ponding water. Make sure that the gutters are functional, and that water is being dumped away from the property.

Get Residents Involved in Stopping Mold Growth

Include your residents in the site's mold prevention practices. Resident education is the key to getting them to make changes in their habits and units to prevent mold.

A good first step is to provide residents with information about mold, potential health effects, and ideas for preventing its growth. Check the HUD and EPA Web sites for downloadable brochures and fact sheets that you can distribute at your site.

“Resident education and orientation are very important,” says Cheung. “You can set the tone from the beginning that mold prevention is a shared responsibility.”

Don't just provide the information once at the beginning of a tenancy and then forget about it. Hold occasional meetings to reinforce household mold prevention practices and to provide updates and information. (See the box for mold prevention tips to distribute to your residents.)

“Use a strategic approach when educating your residents on mold prevention,” Cheung says. “If you overwhelm them with information, they won't read it.”

PRACTICAL POINTER: Residents who don't report leaks or who maintain high levels of humidity in their units may be encouraging mold growth. As a preventive measure, many tax credit sites are asking residents to sign a lease addendum that spells out residents’ responsibilities regarding mold. For details on what your addendum should say, as well as a Model Lease Addendum, see “Hold Residents Accountable for Preventing Mold Growth,” Insider, December 2008, p. 1.

Insider Sources

Hung Cheung, MD, MPH, FACOEM: President, Dr. Cheung/OEM Advisor, LLC, 1421 Clarkview Rd., Ste. 100, Baltimore, MD 21209; 1-888-361-8882;;

Daniel Tranter: Research Scientist, Indoor Air Unit, Minnesota Dept. of Health, 625 Robert St. N, P.O. Box 64975, St. Paul, MN 55164-0975; 1-800-789-9050;


Mold Prevention: Tips for Residents

What can your residents do to prevent mold growth in their units? The following are a few of HUD's action steps for preventing mold in the home:

  • Keep surfaces clean and dry—wipe up spills and overflows right away.

  • Store clothes and towels clean and dry—do not let them stay wet in the laundry basket or washing machine.

  • Don't leave water in drip pans, basements, and air conditioners.

  • If the humidity is high, don't keep a lot of houseplants.

  • Wipe down shower walls with a squeegee or towel after bathing or showering.

  • Cut down the steam in the bathroom while bathing or showering. Run a fan that vents to the outside or open a window.

  • Run a fan that vents to the outside when cooking.

  • Report leaks promptly.

  • Increase airflow in problem areas—open closet doors and move furniture away from outside walls where mold is growing. Move your furniture around occasionally.

  •  Clean up mold with a mix of laundry detergent or dishwashing soap and water, or chlorine bleach with soap and water. (Never mix chlorine bleach with products that contain ammonia or acids.)

Source: “Help Yourself to a Healthy Home: Mold and Moisture,” HUD,


Mold Prevention: Tips for Maintenance

The EPA recommends the following tips for preventing moisture and controlling mold:

  • When water leaks or spills occur indoors, act quickly. If wet or damp materials or areas are dried 24 to 48 hours after a leak or spill happens, in most cases, mold will not grow.

  • Fix plumbing leaks and other water problems as soon as possible. Dry all items completely.

  • Clean and repair roof gutters regularly.

  • Make sure the ground slopes away from the building foundation, so that water does not enter or collect around the foundation.

  • Vent appliances that produce moisture, such as clothes dryers, stoves, and kerosene heaters to the outside where possible.

  • Keep indoor humidity low. If possible, keep indoor humidity below 60 percent (ideally between 30 and 50 percent) relative humidity.

  • If you see condensation or moisture collecting on windows, walls or pipes, act quickly to dry the wet surface and reduce the moisture/water source. Condensation can be a sign of high humidity.

Source: “A Brief Guide to Mold, Moisture, and Your Home,” EPA,


Mold Cleanup: Dos and Don'ts

  • Fix plumbing leaks and other water problems as soon as possible. Dry all items completely.

  • Scrub mold off hard surfaces with detergent and water, and dry completely.

  • Thow away absorbent or porous materials, such as ceiling tiles and carpet, if they become moldy. Mold can grow on or fill in the empty spaces and crevices of porous materials, so the mold may be difficult or impossible to remove completely.

  • Don't paint or caulk moldy surfaces. Clean up the mold and dry the surfaces before painting. Paint applied over moldy surfaces is likely to peel.

  • Don't breathe in mold or mold spores. Make sure maintenance staff limit their exposure to airborne mold by wearing an N-95 respirator.

  • Wear gloves. Long gloves that extend to the middle of the forearm are recommended. When working with water and a mild detergent, ordinary household rubber gloves may be used. If using a disinfectant, a biocide such as chlorine bleach, or a strong cleaning solution, select gloves made from natural rubber, neoprene, nitrile, polyurethane, or PVC. Avoid touching mold or moldy items with bare hands.

  • Wear goggles. Goggles that do not have ventilation holes are recommended. Avoid getting mold or mold spores in the eyes.

Source: “A Brief Guide to Mold, Moisture, and Your Home,” EPA,

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