Mold in the Basement

Learn about mold in the basement, basement mold removal, and how to prevent the growth of basement mold.


A moldy basement wall caused by water damage.

Photo by: Amy Walters

Amy Walters

Mold can grow anywhere it can find oxygen, moisture and organic material, and it's particularly happy in damp, humid areas of the home — so it's no surprise that mold in the basement is a common problem for homeowners.

Healthy Home Myths Debunked

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Myth: A tight building envelope results in poor indoor air quality.

Reality: Poor indoor air quality (IAQ) is often a result of a leaky house, which allows uncontrolled air to pass through the building envelope. The nonprofit Building Performance Institute, which develops standards for residential energy efficiency retrofits, explains: "Warm, moist conditioned air passes from the living space though the walls on its way outside. When that warm air reaches the cooler temperatures within the wall cavity or inside a window frame, it drops the moisture on condensing surfaces, which can help contribute to mold." Distribution of carbon monoxide from an attached garage into the home is another consequence of a leaky home, according to the American Lung Association.

As part of a building performance evaluation (or energy audit), a certified contractor uses a blower door to depressurize the home and locate air migration pathways that need to be sealed. The cost of an evaluation ranges from $250 to $500, a fee some municipalities subsidize through the Energy Star program.

Myth: The best way to eliminate mold is to bleach it into oblivion.

Reality: Mold is evidence that a moisture issue — a leak or condensation — along with the organic material found in construction materials, is allowing microscopic mold spores to go forth and multiply like crazy. However, in most cases, the EPA does not recommend the use of biocides like bleach: "It is not possible or desirable to sterilize an area; a background level of mold spores will remain – these spores will not grow if the moisture problem has been resolved."

What's more, dead mold may still cause allergic reactions in some people, so it is not enough to simply kill the mold. It must also be removed. Scrub the area with a strong detergent (wear rubber gloves and protective clothing), and then ventilate the space and allow it to thoroughly dry out. For large outbreaks, call in the pros and replace any absorbent building materials.

Be aware of the telltale signs of mold, which include dampness, odors, discoloration, peeling paint, condensation, compacted insulation and nasty black or green fuzzy blotches.

Myth: New homes are built with radon-resistant features.

Reality: There is no federal law requiring radon testing or radon-resistant construction features, even though the U.S. Department of Housing and Urban Development (HUD) reports that about one in 15 homes has a radon problem and attributes 21,000 deaths a year to the naturally occurring radioactive gas. Exposure to radon, which can seep into a home and build up over time, is generally symptomless; you can't smell or see radon gas and it can take up to 20 years of exposure before you develop lung cancer.

"People mistakenly assume radon isn't a threat anymore since it hasn’t gotten as much media attention as it did in the 1980s, when it was identified as a carcinogen. But radon in homes is the leading cause of lung cancer among nonsmokers," says Rebecca Morley, executive director of the nonprofit National Center for Healthy Housing. "They think it either went away or that there are new regulations to protect them."

The EPA encourages homeowners to have their houses tested for radon. Quick tests ($8-$25) take three to seven days and are available at hardware stores and online; a 90-day continuous monitoring assessment (about $25 for a DIY kit; $150 for a professional inspection), which accounts for peaks and lows, will produce more thorough results. If your home has more than 4 pCo/L (picocuries per liter of air), hire a professional contractor to seal cracks and to install a venting system. You can also reduce your risk by increasing natural ventilation throughout the house and not smoking.

Myth: Grab bars are just for old folks.

Reality: "Grab bars in bathrooms and showers are for everybody," says Meri-K Appy, president of Safe Kids USA. "Thousands of kids wind up in hospital emergency rooms every year because of falls in the tub or shower." She recommends installing a sturdy and well-positioned grab bar in an area where a wet, slippery surface may spell danger.

To make stairs, another area where people are prone to fall, safer, experts also suggest stair rails on both sides. A strip of chair molding on one side won't cut it. Stair rails should be 34 inches high and guardrails 36 inches high.

Myth: Installing a vapor barrier is the best way to prevent moisture in walls.

Reality: Not so, says the U.S. Department of Energy: "Vapor barriers only retard moisture due to diffusion, while most moisture enters walls either through fluid capillary action or as water vapor through air leaks." There is a lot of confusion among homeowners and contractors about vapor barriers (a layer with a permeability rating of 0.1 perm or less) and vapor retarders (a layer with permeability greater than 0.1 perm but less than or equal to 1 perm). Both slow the transmission of vapor through a building assembly, but their effectiveness depends a lot on your climate zone. The prime consideration for homeowners is the structure's ability to dry out, which leads many experts to question whether vapor barriers are necessary at all.

Whatever your climate, the DOE recommends three basic measures to control moisture: installing a polyethylene ground cover on the earth floor of a house with a crawlspace and sloping the ground away from the foundation of the house; installing a continuous vapor barrier in a climate zone with a perm rating of less than 1; and placing a termite shield, sill gaskets or other vapor-impermeable membrane on the top of the foundation wall to prevent moisture from wicking into the framed wall from the concrete foundation wall by capillary action.

Myth: Water damage from fire sprinklers is almost worse than fire damage.

Reality: This perception stems from the belief that when one fire sprinkler head goes off, they all do. In modern residential systems, says Meri-K Appy, president of Safe Kids USA, heads are individually activated by high heat so only those — usually one or two — closest to a fire go off.

The beauty of a home fire sprinkler is that it is activated when a fire is still very small, which can buy precious time when one is trying to evacuate the home.

Myth: Fiberglass insulation causes cancer.

Reality: This is a tricky one. At one time fiberglass was linked to cancer, but in 2001, the International Agency on Cancer Research (IACR) removed fiberglass from its "possibly carcinogenic to humans" list. However, fiberglass does emit a synthetic material called styrene, which the IACR and the EPA say is a possible carcinogen.

Either way, you don't want to roll around in the stuff. Fiberglass is a man-made silicate fiber made from very fine strands of glass. According to the American Lung Association, inhaling these fibers can reduce lung function and cause inflammation in humans and animals as well as skin, eye and throat irritation.

If you work with fiberglass, wear loose-fitting, long-sleeved clothing — which you should wash separately from other clothing — goggles and a nose/mouth mask. Open a window to increase ventilation and wet-vac the dust and fibers.

Myth: Air purifiers cure allergies.

Reality: According to the EPA, "While air-cleaning devices may help to control the levels of airborne allergens, particles or, in some cases, gaseous pollutants in a home, they may not decrease adverse health effects from indoor air pollutants."

In short, air cleaners can't hurt, but they don't perform miracles, and given their cost ($70-$1,600 for portable units; $30-$295 for replacement filters), you might be better off installing a whole-house HEPA furnace filter, ventilating your house and cleaning vigilantly with a HEPA-filter vacuum.

Avoid ozone generators that are marketed as air cleaners. Despite pseudoscientific marketing claims that they control indoor air pollution with things like "energized oxygen" or "pure air," they in fact dispense large concentrations of ozone, a toxic gas with vastly different chemical and toxicological properties from oxygen, which even in small concentrations can cause serious health problems. For this reason, be aware that most electrostatic ionizers also produce some ozone. Just remember the EPA adage for ozone: "Good up high, bad nearby."

If you do go shopping for air cleaners, look for ones with HEPA filters and a CADR (Clean Air Delivery Rate) suitable for your room.

Basement mold is often the result of a source of moisture — leaky foundations or condensation from appliances are typical culprits. One of the first steps in the prevention of basement mold is to ensure that your basement is free of any moisture and doesn't support a damp, humid environment where mold can thrive.

If mold in the basement is already a problem in your home, there are many options for the control and removal basement mold. Depending on the extent and severity of the problem, and the type of mold, you may need to explore options for professional mold removal. In particular, cases of severe toxic black mold growth may require professional care.

For nontoxic species of mold and less severe mold growth, there are many DIY solutions for the prevention and control of mold in the basement. After removing any mold-covered debris, such as dry wall, insulation, carpet or sub-flooring, hard surfaces can be treated with commercial products containing ammonia and bleach. Basement mold removal on tile or linoleum can also be performed with vinegar or a borax and water solution.

Mold in the basement is a common problem, but by understanding how to identify problem areas and prevent and control mold growth, you can avoid the potentially costly and unhealthy spread of basement mold.

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