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Page updated Apr 2, 2014 2:48 PM

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Source Specific Controls 

Environmental Tobacco Smoke 

Environmental tobacco smoke (ETS) is the mixture of smoke that comes from the burning end of a cigarette, pipe, or cigar, and from smoke exhaled by the smoker. It is a complex mixture of over 4,000 compounds, more than 40 of which are known to cause cancer in humans or animals, and many of which are strong irritants. ETS is often referred to as "secondhand smoke" and exposure to ETS is often called "passive smoking."

The health effects from smoking and from breathing ETS are extensive and well understood. They range from lung cancer to emphysema, and also act to exacerbate a wide range of pre-existing respiratory conditions. Children are particularly susceptible to adverse health effects from exposure to ETS.
Reducing exposure to ETS is relatively simple:

  • Don't smoke inside your home or permit others to do so. Ask smokers to smoke outdoors.
  • If smoking indoors cannot be avoided, increase ventilation in the area where smoking takes place.
  • Do not smoke if children are present, particularly infants and toddlers.

For more information, visit the Alexandria Health Department's Smoke Free Initiative (link to come).  Additional information is available from the Environmental Protection Agency (EPA) and the American Lung Association (ALA).


Exposure to lead can occur through drinking water, food, contaminated soil, deteriorating paint, and dust. Before it was known how harmful lead could be, it was used in paint, gasoline, water pipes, and many other products. Lead-based paint is the most significant source of lead exposure in the U.S. today.

Lead affects practically all systems within the body. At high levels it can cause convulsions, coma, and even death. Lower levels of lead can adversely affect the brain, central nervous system, blood cells, and kidneys.

Elevated blood lead levels affect an estimated 13,800 children under the age six in Virginia. The effects of lead exposure on fetuses and young children can be severe. They include delays in physical and mental development, lower IQ levels, shortened attention spans, and increased behavioral problems. Children may have higher exposures since they are more likely to get lead dust on their hands and then put their fingers or other lead-contaminated objects into their mouths.

The primary source is dust from lead-based paint in many of Virginia’s 1.8 million homes built before 1978. Harmful exposures to lead can be created when lead-based paint is improperly removed from surfaces by dry scraping, sanding, or open-flame burning.

There are many ways to reduce exposure to lead in homes:

  • Keep areas where children play as dust-free and clean as possible.
  • Leave lead-based paint undisturbed if it is in good condition - do not sand. or burn off paint that may contain lead.
  • Do not try to remove lead paint yourself.
  • Find out about lead in drinking water.

For more information on lead, check with the Environmental Health Division, the Virginia Department of Health and the EPA.


The most common source of indoor radon is uranium in the soil or rock on which homes are built. As uranium naturally breaks down, it releases radon gas (a colorless, odorless, radioactive gas). Radon gas enters homes through dirt floors, cracks in concrete walls and floors, floor drains, and sump pumps. When radon becomes trapped in buildings, exposure can become a concern.

The predominant health effect associated with exposure to elevated levels of radon is lung cancer. Research suggests that swallowing water with high radon levels may pose risks too (although these are believed to be much lower than those from breathing air containing radon).

There are many kinds of inexpensive, easy-to-use radon test kits that you can get through the mail, in hardware stores, and other retail outlets. Make sure that you buy a test kit that has passed EPA's testing program or is state-certified.

You can learn more about radon through EPA's publications, A Citizen's Guide to Radon: The Guide to Protecting Yourself and Your Family from Radon and Home Buyer's and Seller's Guide to Radon. Ways to reduce radon in your home are discussed in EPA's Consumer's Guide to Radon Reduction. You can also get assistance from the Virginia Department of Health’s Indoor Radon Program.

Combustion Products 

The major constituents of combustion products are carbon monoxide, nitrogen dioxide, and particles. Potential sources of these pollutants in your home include woodstoves, fireplaces, gas stoves, and unvented kerosene/gas space heaters.  Improperly installed or maintained chimneys/flues and cracked furnace heat exchangers can also emit combustion gases and particles. Fireplaces and woodstoves without a dedicated outdoor air supply can ‘back-draft’, causing combustion product emissions into the living space.

Carbon monoxide (CO) is a colorless, odorless gas that interferes with the delivery of oxygen throughout the body. At high concentrations it can cause unconsciousness and death. Lower concentrations can cause a range of symptoms from headaches, dizziness, weakness, nausea, confusion, and disorientation, to fatigue in healthy people and episodes of increased chest pain in people with chronic heart disease. For more information, check with the City of Alexandria’s Fire Department, the EPA or the ALA. 

Nitrogen dioxide (NO2) is a colorless, odorless gas that irritates the mucous membranes in the eye, nose, and throat and causes shortness of breath after exposure to high concentrations. There is evidence that high concentrations or continued exposure to low levels of nitrogen dioxide increases the risk of respiratory infection; there is also evidence from animal studies that repeated exposures to elevated nitrogen dioxide levels may lead, or contribute, to the development of lung disease such as emphysema. People at particular risk from exposure to nitrogen dioxide include children and individuals with asthma and other respiratory diseases. For more information, check with the EPA.

To reduce exposure from combustion products in homes:

  • Take special precautions when operating fuel-burning unvented space heaters.
  • Install and use exhaust fans over gas cooking stoves and ranges and keep the burners properly adjusted.
  • Keep woodstove emissions to a minimum. Choose properly sized new stoves that are certified as meeting EPA emission standards.
  • Have central air handling systems, including furnaces, flues, and chimneys, inspected annually and promptly repair cracks or damaged parts.
  • Install CO monitors in several areas of your home.

For more detailed information check with the Consumer Product Safety Commission (CPSC), the EPA, and the ALA.

Household Products 

Organic chemicals are widely used as ingredients in household products. Paints, varnishes, and wax all contain organic solvents, as do many cleaning, disinfecting, cosmetic, degreasing, and hobby products. Fuels are made up of organic chemicals. All of these products can release organic compounds while you are using them, and, to some degree, when they are stored.

EPA studies have found levels of about a dozen common organic pollutants to be 2 to 5 times higher inside homes than outside, regardless of whether the homes were located in rural or highly industrial areas. Additional studies indicate that while people are using products containing organic chemicals, they can expose themselves and others to very high pollutant levels, and elevated concentrations can persist in the air long after the activity is completed.

The ability of organic chemicals to cause health effects varies greatly, from those that are highly toxic, to those with no known health effect. As with other pollutants, the extent and nature of the health effect will depend on many factors including the level of exposure and the length of time exposed. Eye and respiratory tract irritation, headaches, dizziness, visual disorders, and memory impairment are among the immediate symptoms that some people have experienced soon after exposure to some organics. At present, not much is known about what health effects occur from the levels of organics usually found in homes.

To reduce exposures to toxic household products:

  • Use household products according to manufacturer’s directions.
  • Use them outdoors or in well-ventilated places.
  • Throw away unused or little-used containers safely; buy in quantities that you will use soon.
  • Use nontoxic alternatives.

Check with the EPA for more detailed information on toxic household products.


Asbestos is a mineral fiber that has been used in a variety of building construction materials for insulation and as a fire-retardant. The EPA and CPSC have banned several asbestos products and manufacturers have also voluntarily limited certain uses of asbestos. Today, it is most commonly found in older homes in pipe and furnace insulation materials, asbestos shingles, millboard, textured paints and other coating materials, and floor tiles.

The most dangerous asbestos fibers are too small to be visible. After they are inhaled, they can remain and accumulate in the lungs. Asbestos can cause lung cancer, mesothelioma (a cancer of the chest and abdominal linings), and asbestosis (irreversible lung scarring that can be fatal). Symptoms of these diseases do not show up until many years after exposure began. Most people with asbestos-related diseases were exposed to elevated concentrations on the job.

Usually it is best to leave asbestos material that is in good condition alone as it will not release asbestos fibers. There is no danger unless fibers are released and inhaled into the lungs. Before you have your house remodeled, find out whether asbestos materials are present.

If you are concerned about exposure to asbestos in your home, clean with a wet rag or mop; vacuum with a vacuum cleaner that has a high efficiency particulate air (HEPA) filter; and/or steam clean.  If you are unsure about asbestos removal, contact a professionally trained contractor.  Select a contractor only after careful discussion of the problems in your home and the steps the contractor will take to clean up or remove them.  Consider the option of sealing off the materials instead of removing them. Refer to the City of Alexandria’s Office of Environmental Quality and the EPA for more detailed information on this topic  


In homes, the most significant sources of formaldehyde are likely to be pressed wood products made using adhesives that contain urea-formaldehyde (UF) resins. The rate at which products like pressed wood or textiles release formaldehyde can change. Formaldehyde emissions will generally decrease as products age. When the products are new, high indoor temperatures or humidity can cause increased release of formaldehyde from these products.

Formaldehyde, a colorless, pungent-smelling gas, can cause watery eyes, burning sensations in the eyes and throat, nausea, and difficulty in breathing in some humans exposed at elevated levels (above 0.1 parts per million). High concentrations may trigger attacks in people with asthma. There is evidence that some people can develop sensitivity to formaldehyde. It has also been shown to cause cancer in animals and may cause cancer in humans.

To reduce exposures to formaldehyde, ask about the formaldehyde content of pressed wood products, including building materials, cabinetry, and furniture before you purchase them.

For more information on formaldehyde, check with the EPA.


According to a recent survey, 75 percent of U.S. households used at least one pesticide product indoors during the past year. Products used most often are insecticides and disinfectants. Another study suggests that 80 percent of most people's exposure to pesticides occurs indoors and that measurable levels of up to a dozen pesticides have been found in the air inside homes. Pesticides used in and around the home include products to control insects (insecticides), termites (termiticides), rodents (rodenticides), fungi (fungicides), and microbes (disinfectants). They are sold as sprays, liquids, sticks, powders, crystals, balls, and foggers.

In 1990, the American Association of Poison Control Centers reported that some 79,000 children were involved in common household pesticide poisonings or exposures. In households with children under five years old, almost one-half stored at least one pesticide product within reach of children.
Both the active and inert ingredients in pesticides can be organic compounds; therefore, both could add to the levels of airborne organics inside homes. Both types of ingredients can cause the effects discussed in this document under ‘Household Products’; however, as with other household products, there is insufficient understanding at present about what pesticide concentrations are necessary to produce these effects.

To reduce exposures to toxic pesticides:

  • Read the label and follow the directions. It is illegal to use any pesticide in a manner inconsistent with the directions on its label.
  • Ventilate the area well after pesticide use.
  • Use non-chemical methods of pest control when possible.
  • If you decide to use a pest control company, choose one carefully.
  • Dispose of unwanted pesticides safely.
  • Keep exposure to moth repellents to a minimum.
  • Mix or dilute outdoors.
  • Apply only in recommended quantities.
  • Take plants or pets outside, where possible.
  • Do not store unneeded pesticides inside your home.

For more information on pesticides, check with the Virginia Department of Agriculture and Consumer Services, the Virginia Department of Health and the EPA.

Biological Agents 

Molds are organisms that are found indoors and outdoors, are part of the natural environment and play an important role in the environment by breaking down and digesting organic material. Also called fungi or mildew, molds are neither plants nor animals; they are part of the kingdom Fungi. Molds can multiply by producing microscopic spores (2 - 100 microns [µm] in diameter), that function similarly to the seeds produced by plants. Many spores are so small they easily float through the air and can be carried for great distances by even the gentlest breezes. The number of mold spores suspended in indoor and outdoor air fluctuates from season to season, day to day, and even hour to hour.

Mold spores cannot be eliminated from indoor environments. Some mold spores will be found floating through the air and in settled dust; however, they will not grow if moisture is not present. Mold is not usually a problem indoors unless they land on a wet or damp surface and begin growing. Therefore, the most important thing you can do to prevent mold infestations in your home is to eliminate sources of moisture.

Allergic reactions to mold are common and can be either immediate or delayed. Repeated or single exposure to mold, mold spores, or mold fragments may cause non-sensitive individuals to become sensitive to mold, and repeated exposure has the potential to increase this sensitivity. Allergic responses include hay fever-like symptoms such as headache, sneezing, runny nose, red eyes, and skin rash. Molds can cause asthma attacks in people with asthma who are allergic to mold. In addition, molds can irritate the eyes, skin, nose, throat, and lungs of individuals whether or not they are allergic to mold. Breathing in mold may also cause hypersensitivity pneumonitis, an uncommon disease that resembles bacterial pneumonia. In addition, mold exposure may result in opportunistic infections in persons whose immune systems are weakened or suppressed.

When mold grows indoors, occupants may begin to report odors and a variety of symptoms that may be associated with exposure to mold. But all of these symptoms may be caused by other exposures or conditions unrelated to mold growth. Therefore, it is important not to immediately assume that, whenever any of these symptoms occurs, mold is the cause. 

Some compounds produced by molds have strong smells, are volatile and are quickly released into the air. These compounds are known as microbial volatile organic compounds (mVOCs). Because mVOCs often have strong or unpleasant odors, they can be the source of the "moldy odor" or musty smell frequently associated with mold growth. A moldy odor suggests that mold is growing in your house and should be investigated.>

The health effects of inhaling mVOCs are largely unknown, although exposure to mVOCs has been linked to symptoms such as headaches, nasal irritation, dizziness, fatigue, and nausea. More research is needed to determine whether there are any human health effects from non-occupational indoor exposures to mVOCs.

Mold can grow on virtually any organic material as long as moisture and oxygen are present. There are molds that grow on wood, paper, carpet, food, and insulation. Because mold eats or digests what it is growing on, it can damage a building and its furnishings. If left unchecked, mold eventually can cause structural damage to building materials. You can prevent damage to your home and contents, save money, and avoid potential health problems by controlling moisture and eliminating mold growth. Eliminating all mold and mold spores indoors is virtually impossible, but controlling indoor moisture will control the growth of indoor mold.

Moisture problems can have many causes. Some moisture problems have been linked to changes in building construction practices since the 1970s. These practices led to buildings that are tightly sealed but, in some cases, lack adequate ventilation. Without adequate ventilation, moisture may build up indoors and mold may grow.

Delayed or insufficient maintenance can lead to moisture problems in buildings. Undiscovered or ignored moisture problems can create an environment in which mold can grow. Common moisture problems include:

  • Leaking roofs.
  • Leaking or condensing water pipes, especially pipes inside wall cavities or pipe chases.
  • Landscaping gutters, and down spouts that direct water into or under a building.
  • High humidity (> 60% relative humidity).
  • Unvented appliances such as clothes dryers vented into a garage. (Clothes dryers should be vented to the outside.)

Some moisture problems are not easy to see (for example, the inside of walls). Mold is frequently found on walls in cold corners behind furniture where condensation forms. Other possible locations of hidden moisture, resulting in hidden mold growth are:

  • Poorly draining condensate drain pains inside air handling units.
  • Porous thermal or acoustic liners inside duct work.
  • Roof materials above ceiling tiles.
  • The back side of drywall, paneling, and wallpaper.
  • The underside of carpets and pads.

You may suspect mold, even if you can't see it, if your home smells moldy. Sometimes, humidity or dampness (water vapor) in the air can supply enough moisture for mold growth. Indoor relative humidity (RH) should be kept below 60 percent — ideally between 30 percent and 50 percent, if possible. Low humidity may also discourage pests (such as cockroaches) and dust mites.

Humidity levels can rise in a house as a result of the use of humidifiers, steam radiators, moisture-generating appliances such as dryers, and combustion appliances such as stoves. Cooking and showering also can add to indoor humidity.

One function of the building heating, ventilation, and air conditioning (HVAC) system is to remove moisture from the air before the air is distributed throughout the building. If the HVAC system is turned off during or shortly after major cleaning efforts that involve a lot of water, such as mopping and carpet shampooing or cleaning, the humidity may rise greatly, and moisture or mold problems may develop.

Condensation can be a sign of high humidity. When warm, humid air contacts a cold surface, condensation may form. (To see this, remove a cold bottle of water from a refrigerator and take it outside on a hot day. Typically, condensation will form on the outside of the bottle.) Humidity can be measured with a humidity gauge or meter; models that can monitor both temperature and humidity are generally available for less than $50 at hardware stores or on the Internet.

Areas that are always or often damp, such as bathrooms, laundry/utility rooms, and basements, are common locations for mold growth in homes. Regularly check areas that have been or are likely to get wet. If you hire a home inspector, building inspector, or other professional to locate a water or mold problem, make sure the professional has experience identifying and locating mold and water problems. Check references and look for membership in professional organizations.

If possible, dry all items within 24-48 hours of their becoming wet.

To dry carpet and backing within 48 hours, remove water with a wet vacuum, pull the carpet and pad off the floor, and dry them using a fan to blow air over them. A dehumidifier can be used to reduce the humidity in the room where the carpet and backing are drying, while fans can be used to accelerate the drying process.

Water can be removed from concrete or cinder block surfaces with a water-extraction vacuum. The drying also can be accelerated by using dehumidifiers, fans, and heaters.

Hard surface flooring (such as linoleum, ceramic tile, and vinyl) should be vacuumed or damp wiped with a mild detergent and allowed to dry. They should be scrubbed clean, if necessary. If the under-flooring is wet, it should be dried using a vacuum or by exposing it to the air.

Non-porous, hard surfaces such as plastics and metals should be vacuumed or damp wiped with water and mild detergent, then allowed to dry. Scrubbing may be necessary to thoroughly clean the surfaces.

Water should be removed from upholstered furniture with a water-extraction vacuum. Fans, dehumidifiers, and heaters may be used to accelerate the drying process. Completely drying upholstered furniture within 48 hours may be difficult, so if the piece is valuable, you may consider consulting a restoration or water-damage professional who specializes in furniture.

Drywall, also known as gypsum board or gypsum wallboard, may be dried in place if there is no obvious swelling and the seams are intact. Otherwise, removal is necessary. The wall cavity is the most difficult area to dry, and it should be ventilated if drywall is left to dry in place. (Drywall is not made out of boards of wood; traditionally, drywall is made of the mineral gypsum with a layer of heavy paper on the outside and inside. Commercial gypsum boards and drywall are also available with a variety of outside layers and coatings. According to the U.S. Geological Survey, a typical new home contains more than 7 metric tons of gypsum.)

To clean water-damaged window drapes, follow the manufacturer's laundering or cleaning instructions.

To clean wooden surfaces, remove moisture immediately and use dehumidifiers, fans, and gentle heat to dry them. (Be very careful when applying heat to hardwood floors.) Treated or finished wood surfaces can be cleaned with mild detergent and clean water, then allowed to dry. Wet paneling should be pried from the wall for drying.

Some water-damaged items, including ceiling tiles, cellulose and fiberglass insulation, drywall and gypsum board, and books and papers, may have to be discarded. If valuable or important books, documents, or other items are moldy or water damaged, you may wish to consult a restoration, water damage, or remediation expert.

These guidelines are for damage caused by clean water. If you know or suspect that the water is contaminated with sewage, or with chemical or biological pollutants, then PPE and containment are required by OSHA. An experienced professional should be consulted if you or your remediators do not have expertise remediating in contaminated water situations. Do not use fans until you have determined that the water is clean or sanitary.

Before planning a remediation effort, the size and extent of the mold problem and any continuing moisture problems should be assessed. Remediations generally can be divided into small (less than 10 square feet of mold), medium (10-100 square feet of mold), and large jobs (more than 100 square feet of mold). A remediation manager should be selected for medium or large jobs. You may choose to involve an experienced health and safety professional in remediation projects, particularly on large or complex jobs.

Questions to consider before starting remediation include:

  • Are there existing moisture problems in you house?
  • Have building materials been wet more than 48 hours?
  • Are there hidden sources of water, or is the humidity high enough to cause condensation?
  • Do you notice musty or moldy odors?
  • Are you or other occupants having health problems?
  • Are building materials or furnishings visibly damaged?
  • Has maintenance been delayed?
  • Has your home been remodeled recently?
  • Are consultations with health professionals indicated?

Remediating mold and moisture problems may be complex, and it may increase exposure to mold unless personal protective equipment (PPE) is used.

A variety of methods are available to remediate damage to structures and furnishings caused by moisture-control problems and mold. The procedures selected depend on the size of the moldy area and the type of contaminated materials. Budget may also be a concern. The methods presented in this section outline one approach; some professionals may prefer to use other methods. Cleanup methods may include the following.

Wet, or water-extraction, vacuums are designed to collect water. They can be used to remove water that has accumulated on floors, carpets, and hard surfaces. Wet vacuums should be used only when materials are still wet, otherwise they may spread mold spores. Wet vacuums alone will not dry carpets. Wet carpets must be pulled up and dried, then reinstalled. The carpet padding also must be dried. The tanks, hoses, and attachments of wet vacuums should be thoroughly cleaned and dried after use because mold and mold spores may stick to their surfaces.

Mold can generally be removed from hard surfaces by wiping or scrubbing with water and detergent. Always follow the cleaning instructions on product labels. Surfaces cleaned by damp wiping should be dried quickly and thoroughly to discourage further mold growth. Porous materials that are wet and have mold growing on them may have to be discarded. Because mold will infiltrate porous substances and grow on or fill in empty spaces or crevices, completely removing mold can be difficult, if not impossible. Mold can also cause staining and other cosmetic damage.   

High-Efficiency Particulate Air (HEPA) vacuums are recommended for the final clean up of remediation areas after materials have been thoroughly dried and contaminated materials have been removed. HEPA vacuums are also recommended for cleaning up dust that has settled outside the remediation area. When changing the vacuum filter, workers should wear PPE to prevent exposure to mold that has been captured in the vacuum. The filter and contents of the HEPA vacuum must be disposed of in well-sealed plastic bags. Care must be taken to ensure that the new filter is properly seated on the vacuum so there are no leaks.

Mold-contaminated building materials that cannot be salvaged should be double-bagged in 6-mil or thicker polyethylene bags. The bagged materials usually can be discarded as ordinary construction waste. Packaging mold-contaminated materials in sealed bags before removing them from the containment area is important to minimize the spread of mold spores throughout the home. Large items that have heavy mold growth should be covered with polyethylene sheeting and sealed with duct tape before being removed from the containment area.

For large or complex mold remediation jobs, you may consider hiring professionals who have experience working on large mold remediation projects, particularly since extensive containment and PPE may be needed. Be sure to check references and ensure that the professional has experience working in mold remediation situations. Remediators should follow EPA mold remediation guidance or other government or professional remediation guidance. Occupants need to be informed about what is going to happen, when it will happen, and how they may be affected.

Mold remediation involving a heating, ventilation, and air conditioning (HVAC) system should be done only by professionals experienced in working with HVAC systems. Professionals may have several different methods and techniques for approaching HVAC remediation. As with the rest of a mold remediation project, professional judgment is required when working with HVAC systems, and professionals may use materials, methods, and techniques not mentioned on this webpage.

Locating, Diagnosing and Preventing Mold Growth in Various Areas of Your House:

Hidden Mold: You may suspect hidden mold if a building smells moldy, but you cannot see the source; or if you know there has been water damage. Mold may be hidden in places such as the back side of dry wall, wallpaper, or paneling; the top side of ceiling tiles; the underside of carpets and pads; the inside of walls around pipes (with leaking or condensing pipes); the surface of walls behind furniture (where condensation forms); inside ductwork; and in roofing materials above ceiling tiles (due to roof leaks or insufficient insulation). 

Investigating hidden mold problems may be difficult and will require caution when it involves disturbing potential sites of mold growth. For example, wallpaper removal can lead to a massive release of spores if mold is growing on the underside of the paper. If you believe that you may have a hidden mold problem, consider hiring an experienced professional.

Ventilation (HVAC) Systems: HVAC systems are a frequent source of moisture problems in a home, creating favorable conditions for mold growth both within and surrounding them.  They should be inspected and maintained by a qualified HVAC contractor at least once per year and the following factors should be considered, particularly if you suspect that you may have HVAC-related moisture or mold problems.

The condensate drain pan, located under the air conditioning cooling coils, is a frequent source of problems in the home (see Figure 1). As the air passes through the coils it is cooled, resulting is condensation and a lowering of the relative humidity. In a properly functioning system, all of the condensate is collected in the pan, and is safely drained away.

Problems occur when the condensate doesn’t drain, or when the pan leaks or overflows. When drainage is the problem, the condensate stagnates and a biofilm can form on the surface. Mold and bacteria thrive in this environment and can enter your home through the supply air. If the pan leaks or overflows, surfaces surrounding the HVAC unit can become saturated with water resulting in significant mold growth. If these problems occur:

  • Make sure that the drain lines are not clogged, and are large enough to prevent a recurrence of the problem.
  • The condensate pan may need to be replaced if there is significant rusting or scale formation, or if it is leaking. Ensure that the replacement pan is properly sloped for efficient drainage.

To reduce the risk of sewer gases entering the HVAC system, make sure that all drain lines are properly trapped.

Air leakage from ductwork is another potential problem area; particularly if the air handling equipment is located in an unconditioned space (leakage also results in a major waste of energy). Supply duct leakage introduces heat and water vapor into areas such as attics, basements or crawl spaces that need to remain dry to prevent mold growth. Air leakage into return ducts from unconditioned spaces can result in elevated relative humidity in occupied areas of your house. Ductwork leakage can also create undesirable pressure differentials between rooms, conditioned and unconditioned spaces, and the house and the outdoors. During regular mechanical system maintenance, it is beneficial to have the degree of duct leakage evaluated, and all joints and seams re-sealed as necessary. Ductwork also needs to be properly insulated, both as an energy-saving measure and to prevent condensation problems in unconditioned spaces during the cooling season.

If you’re having problems keeping the relative humidity down in the summer months (the air may seem cold and clammy or surfaces feel damp), have your maintenance provider determine if you have an oversized cooling system. Modern cooling equipment has become very efficient at removing heat, so it doesn’t have to run very long to adequately cool the house (if oversized, it may only have to be on for several minutes). Unfortunately, this does not allow adequate time for dehumidification to take place in the cooling coils, and it is difficult to maintain relative humidity levels below 60% during the cooling season. If this is the case, see if your service provider can adjust the system to increase cooling cycle. Otherwise, it may be necessary to purchase portable or in-line dehumidifiers.

Attics: Attics are a prime location for water leakage and condensation problems, and should be periodically inspected for signs of moisture or mold growth. This has an added benefit to a homeowner because solving the underlying causes of moisture in the attic can reduce energy costs and prevent damage to the roof and ceiling structures.

Although problems can occur throughout the year, most happen during the winter months when warm air from the house infiltrates the attic and condenses on cold surfaces. This may be caused by insufficient ceiling insulation, air leaks, or both. The most effective way to prevent this is to keep the attic as cold as possible by reducing air leakage/heat flow from the house and providing uniform venting of the space. 

There are several ways to determine if you have a problem. During the winter observe the roof following a snowfall. If the snow melts unevenly or quicker than your neighbors (given similar solar loads), there is a good chance that your attic is too warm and condensation/mold growth may be occurring. Similarly, there may be a problem if snow and ice accumulate near the eaves of the roof, forming an ‘ice dam’.  

Another way to locate problems any time of the year is to go up in the attic and observe both exposed and hidden surfaces looking for moisture, stains, deteriorating lumber, or mold growth. Check the ceiling substrate beneath the insulation, the roof sheathing/rafters, the surfaces on or below the air handling units/ductwork, the ceiling insulation, and the spaces within the eaves/overhangs. See if there is a ‘musty’ odor in the attic space.

If you locate mold growth or water-related problems, try to determine the source of the moisture (leakage, condensation, or both). For example, if the problem area is located:

  • On the ceiling insulation under a stained section of roof sheathing, you probably have a roof leak.
  • On the roof sheathing and rafters, but not the surface below, you probably have a condensation problem.
  • Only in the spaces within the perimeter eaves, you probably have a condensation and leakage problem (ice dams).

Certain attic-related moisture/mold problems can be very complex, and not easy to diagnose and successfully solve. For these, consider retaining a qualified contractor to assist you. Once you have a good idea of the source of the problem, you can identify the necessary corrective measures.

For roof leaks:

  • Determine if there are any penetrations (chimneys, pipes, exhausts, etc.) on the roof above the leak; replace or repair any flashing or other seals.
  • Clean out the gutters if the leaks are located at the perimeter of the roof.
  • Add or repair drainage to flat areas of the roof to prevent pooling or retainage of water.
  • Replace damaged shingles or underlying waterproofing material.

For condensation problems:

  • Add addition ceiling insulation if it is determined that the existing R-value is insufficient.
  • Check to see if there is adequate venting for the attic.
  • Locate any air leaks through the ceiling to the attic. These usually occur through lighting fixtures, pipe/exhaust penetrations, or around the building perimeter/wall lines.
  • Check for supply duct or air handling (AHU) unit leakage if they are located in the attic; seal all seams and joints, and install/repair insulation.

For HVAC leaks, or direct condensation problems:

  • Check for, clean up, and repair any leakage related to the condensate pans.
  • Make sure that all ductwork and the air handling unit are adequately insulated.

Basements: Basements, whether finished or unfinished, conditioned or unconditioned constitute a significant source of moisture infiltration into a home, frequently resulting in mold growth. Possible problems include high humidity (and condensation on cool surfaces), water leakage through perimeter foundation walls, and hidden mold in finished wall assemblies. Basements are also subject to periodic flooding from internal sources, such as water heaters, cloth washers, plugged drains/sumps, or miscellaneous sources from the floors above. Besides the obvious mold and air quality issues, basement moisture problems can have a large, negative and expensive impact on the durability of the entire house.

In an unfinished basement, moisture and mold problems are usually fairly obvious:

  • There are visible mold plumes growing on floor, wall or other surfaces.
  • The air is noticeably stuffy and damp, and there is an obvious musty, mildew-like odor.
  • The foundation walls are damp and water may be pooled around the perimeter of the floor.
  • Carpeting is damp or water-stained, and/or tiles are brittle or lifting.
  • There is condensation on pipes, windows or other surfaces.
  • There are white, chalky stains (efflorescence) on the walls or floor (see Figure 2).
  • Portions of wooden windows, sill plates, columns or beams, particularly those that are in contact with concrete, are wet or decaying.

In a finished basement, many of the above indicators are covered up by wall, floor, and ceiling assemblies, so problems are more difficult to detect. Generally, if the air is stuffy and damp, and/or there is a musty odor, mold is growing in concealed spaces.

The prevention of external water leakage through the foundation and concrete slab actually begins outside of the house; rainwater must be kept away from the house. One of the easiest ways to accomplish this is to make sure that the roof has gutters, and that they are kept clean and unobstructed (including the downspouts). The discharge should also be directed away from the perimeter of the house, preferably by a distance of at least 10 feet.

Next, make sure that the ground around your home’s foundation should be graded to slope down and away from your house at a minimum rate of 1/2” to 1” per linear foot. Finally, make sure that driveways and patios slope and drain away from your house, and that window wells are well drained.

In an unfinished basement (if your basement has a dirt floor, see the section on Crawl Spaces).

Crawl Spaces: Many homes built on crawl space foundations, particularly in humid climates such as ours, experience problems with moisture control and mold. Frequently, these spaces have dirt floors, which are difficult to keep dry and subject to periodic standing water from runoff or groundwater. Even if the soil is apparently dry, it continues to emit soil gases (with a distinctive earthy odor) that contain water vapor and contribute to humidity problems in the space. As there can be many cool surfaces in a crawl space, condensation can contribute significant amounts of moisture.

Besides visible mold growing on surfaces in the crawl space, symptoms of problems include:

  • Musty odors which are periodically noticeable in the living areas
  • Persistent high humidity in the home
  • Condensation on pipes, insulation or other surfaces
  • Insect infestations
  • Deterioration of wooden framing members
  • Buckled hardwood floors

These problems are most prevalent during the summer months but can occur year round. The key to preventing them is keeping the crawl space dry. This somewhat difficult task can be achieved using some or all of the following suggestions:

  • Prevent the introduction of exterior water (see section on external water leakage).
  • Grade the floor to one or more low points and install drains or sump pumps at these locations. If a drainage system already exists, make sure that it is clear and functioning properly.
  • Cover the floor with a suitable air and vapor barrier, including the inside wall and column surfaces (see Figure 3).
  • If HVAC are ductwork extend through the space, make sure that all seams and joints are airtight.
  • Do not discharge bathroom or laundry exhausts into the crawl space; extend them to the building exterior.
  • Seal the perimeter to the extent possible to prevent water leakage and/or the introduction of outside air.
  • Vent the space per code, but ensure that the resulting make-up air is mechanically provided from supply air or from conditioned air from the home.