Why is mold a problem, and how should I get rid of it?

Mold growth is one of the leading causes of indoor air quality problems.  Mold spores are potential allergens, meaning that they can trigger allergic responses much like animal dander or pollen.  In addition, some types of mold produce toxins that can be harmful to humans.  All visible mold growth should be removed from the indoor environment as quickly as possible.

You can clean light mold growth yourself (while using the proper personal protective equipment, including eye protection, gloves, and dust masks), without consulting a professional remediation contractor.  Cleaning methods should include an antifungal detergent and light abrasion to remove all fungal growth.  If the area of mold growth is greater than ten square feet, or if the growth has invaded porous building materials such as drywall, a professional mold remediation contractor should be consulted.

Keep in mind that mold growth is a symptom of a moisture problem.  You can clean it up, but unless you address the source of the moisture, the mold growth will return.  Some moisture problems are easy to diagnose, but often a detailed investigation is needed to uncover the more subtle mechanisms that can cause mold growth.

Should I get samples of my indoor air to check for mold?

Mold sampling should be performed only to determine a specific hypothesis.  If mold growth is already visible, sampling can be a waste of time and money.  Situations where sampling is warranted might be “clearance testing” after mold remediation has been performed or diagnosing the source of unknown respiratory problems.

The type of sample taken is also important.  Many stores sell a mold testing kit that consists of a Petri dish and some instructions, but this type of sample is not particularly useful since it is virtually impossible to quantify how much air was in contact with the growth medium.

Direct surface sampling (via tape-lift or swab) can also be misleading.  Even though the specific type of mold can be identified, there is no real correlation between the amount of mold on a surface and the concentration of spores in the air.

The most commonly used (and most useful) mold sample is taken by passing a precise amount of air across a small sample cassette.  This sample traps both viable and non-viable (meaning both living and dead) spores for laboratory analysis.  This is helpful because dead mold spores can be just as irritating as spores that can produce further mold growth.

What is toxic black mold?

The term “toxic black mold” actually refers to some species of the genus Stachybotrys.  This particular genus of mold can produce mycotoxins that may be harmful to humans. While no definitive link has been proven between Stachybotrys and specific human health problems, anecdotal evidence suggests that this type of mold can cause a wide variety of symptoms. Other types of mold have also been shown to produce mycotoxins that may be harmful to humans, including Aspergillus and Penicillium.

Toxic black mold is actually a misnomer, as many varieties of mold can appear black.  In fact, Stachybotrys can appear in a variety of different colors, including pink.  All black mold growth should not be assumed to be toxic black mold.  However, any mold growth in the home should be removed as soon as possible to prevent allergic reactions or other adverse health effects.

What is relative humidity, and how does it affect mold growth?

The amount of water that can dissolve in a given volume of air depends on the temperature.  Absolutely dry air has a relative humidity of zero percent; completely saturated air has a relative humidity of 100 percent.  Ideally, the relative humidity indoors should be between 35 percent and 55 percent.  If the relative humidity is too low, your skin will dry out and static electricity will increase.  If the relative humidity is too high, condensation will occur on cool surfaces such as windows, air conditioning vents, and floor joists and beams in crawlspaces. This condensation provides the moisture necessary for mold growth.

How can site grading and drainage outside my home affect indoor air quality?

Site grading and drainage play a huge role in indoor air quality.  If surface water is directed towards or trapped against the foundation wall, moisture may enter your basement or crawlspace. This moisture raises the relative humidity of the home, encouraging mold growth.

To keep surface water from entering the home, you should install gutters (provided they are well-maintained and the downspouts discharge at least six feet from the foundation), re-grade the soil near the foundation to ensure the proper slope, and eliminate swales or gullies that direct water towards the home.  Remove accumulations of mulch or organic matter (pine needles, leaves, etc.) against the foundation walls or on the roof that might trap and hold moisture.

Should I be concerned about mold and moisture in my crawlspace?

Yes, because it can rot the floor joists and contaminate the air in the house.

Crawlspaces are not part of the living environment, and are generally not intended to be as clean as the inside of the home. Crawlspaces are often in contact with outside air (through vents), so ambient conditions in a crawlspace tend to approximate those outside.  For this reason, it's important to ensure that crawlspace air cannot travel into the home.  All plumbing insertions and ductwork should be properly sealed to eliminate air movement between the crawlspace and the living space.

To keep soil moisture out of the air in your crawlspace, you should install a polyethylene vapor barrier.  All soil should be covered and all joints should be sealed.  By extending the vapor barrier up the foundation walls and over the crawlspace vents, soil moisture escapes and the crawlspace itself stays dry.

If you don't have a vapor barrier, you should close the crawlspace vents to prevent the influx of humid outdoor air. Crawlspaces should be inspected regularly for moisture problems.

How is my heating, ventilation, and air conditioning (HVAC) system related to indoor air quality?

Proper operation of the HVAC system is the backbone of any indoor air quality plan.  Have a qualified professional inspect your HVAC system and ductwork regularly.

Your thermostat should be set to a temperature that ensures regular system cycling for proper ventilation and dehumidification.  Set the fan to the “AUTO” position instead of "ON" so that the fan does not run constantly.  If the fan continues to run when the compressor shuts off, the outside air that it pulls in is not being dehumidified.  Over time, the indoor relative humidity will increase and mold growth will begin.

Microbial growth (including bacteria, mold, and algae) often occurs in the condensate drain pan, since this area receives a constant supply of moisture during the cooling season. This microbial growth can clog the drain line, resulting in an overflow that can damage underlying building materials.  Inspect the drain pan regularly for signs of microbial growth and add chlorine bleach or an algaecide tablet if necessary.  The discharge point of the condensate drain line should be located outside the home at least six feet away from the foundation.

What else can cause indoor air quality problems?

While mold and moisture are the most common indoor air quality issues, numerous other substances cause problems in the indoor environment.  Radon, for example, is a radioactive gas that occurs naturally in the soil.  When it becomes trapped in a basement or crawlspace, it poses a serious health hazard.  Radon is a common problem in the Southeast, and it is often found in the Atlanta area.

Older homes often contain floor tiles or insulation that was made with asbestos. Asbestos fibers can become airborne if the materials are disturbed, and if inhaled, they can cause mesothelioma, a form of lung cancer.  If asbestos-containing materials (ACM) are in your home, you should disturb them as little as possible.  You should either encapsulate them (such as covering old tiles with a new floor) or have them removed by a professional remediation contractor with asbestos experience.

Other common indoor air quality problems include dust mites, pollen, fiberglass, and volatile organic compounds, or VOCs (such as paint and carpet fumes).  It is possible to check for a wide variety of these indoor pollutants, but there is no one sample that tests for everything.  If you suspect that you have poor indoor air quality, it is best to have a professional perform a complete site inspection to determine the nature of the problem.  Hiring someone to take air samples indiscriminately without knowing the cause of the problem can be a costly process.