Methods Used To Mitigate Mold Hazards In The Home

Guidelines for Mitigation and Personal Protection

Common intervention methods reported in the literature for residential mitigation of mold hazards include:

  • Location and removal of sources of moisture (control of dampness and humidity and repair of water leakage problems).
  • Increasing ventilation.
  • Use of high-efficiency particulate air (HEPA) filters.
  • Maintenance of heating, ventilation, and air conditioning systems.
  • Cleaning of mold contaminated materials.
  • Physical removal of materials with severe mold growth and porous materials that cannot be cleaned.
  • Prevention of spore infiltration from outdoors by closing doors and windows and by using air conditioning.

The literature also consistently emphasizes the importance of worker protection when conducting mold assessment and mitigation projects. Activities such as cleaning or removal of mold-contaminated materials in homes, as well as investigations of mold contamination extent, have the potential to disturb areas of mold growth and release fungal spores and fragments into the air. For example, Vesper measured a very high number of Stachybotrys spores in personal breathing zone samples of a worker during the implementation of a mold remediation program to remove Stachybotrys contaminated materials (i.e., wallboard, paneling and carpeting) from water damaged areas of a home. This suggested that residents should not attempt greater than minor remediation without the proper protection, or preferably should employ a contractor trained in environmental remediation. Recommended measures to protect workers during mold remediation efforts depend on the severity and nature of the mold contamination being addressed, but include the use of well fitted particulate masks or respirators that retain particles as small as 1 micrometers or less, disposable gloves and coveralls, and protective eyewear.

Various guidance documents for remediation of mold contamination have been developed.

  • The New York City Department of Health has a set of guidelines, “Assessment and Remediation of Fungi in Indoor Environments,” that are widely recognized. The document, originally developed for Stachybotrys but expanded to be inclusive of all molds, addresses health effects, environmental assessment, remediation techniques, and hazard communication (available at…).
  • The Institute of Inspection Cleaning and Certification produced guideline S500: Standard and Reference Guide for Professional Water Damage Restoration (available by contacting the IICRC headquarters at (360) 693-5675 or through e-mail at [email protected]).
  • The American Conference of Governmental Industrial Hygienists (ACGIH) bioaerosols committee published in 1999, “Biosaerosols: Assessment and Control,” a compilation of information on investigation strategies, sampling and analysis, and control of indoor bioaerosols, including molds (can be ordered from ACGIH at…).
  • The American Industrial Hygiene Association (AIHA) has recently prepared the “AIHA Mold Guideline on Assessment, Remediation, and Post-Remediation.” It describes a range of methodologies and techniques currently available to conduct assessments of mold growth in residential and commercial buildings. To order, call 703-849-8888.
  • U.S. Environmental Protection Agency published guidance for “Mold Remediation in Schools and Commercial Buildings,” which includes many general principles also applicable to residential mold mitigation efforts (available from EPA online at…).
  • U.S. Environmental Protection Agency published guidance, “A Brief Guide to Mold, Moisture, and Your Home,” for homeowners and renters on how to clean up residential mold problems and how to prevent mold growth (available from EPA online at…).
  • The Canada Mortgage and Housing Corporation published, “Clean-up Procedures for Mold in Houses,” which provides qualitative guidance for mold mitigation (can be ordered from CMHC at…).
  • Health Canada published its “Fungal Contamination in Public Buildings” guide to assist investigators in recognizing and managing fungal contamination (available through Health Canada at… sesc/air_quality/pdf/fungal.pdf).
  • The Institute of Medicine of the National Academies published in 2004 a comprehensive review of the literature on causes, effects, assessment, remediation and prevention of interior dampness and mold. Entitled “Damp Indoor Spaces and Health,” it is available from the National Academies Press at….
  • The Centers for Disease Control and Prevention prepared guidance in 2005 on mold for cleanup and reconstruction efforts following hurricanes, “Mold: Prevention Strategies and Possible Health Effects in the Aftermath of Hurricanes Katrina and Rita.” See chapter 3 on cleanup and prevention and chapter 4 on personal protective equipment (available at…).

Although these and other mold remediation guidance documents share many of the same approaches for conducting residential mitigation of mold hazards, such as correction of moisture problems and removal of severely contaminated materials, specific criteria cited in the guidelines may vary. For example, ACGIH guidance regarding remediation techniques and personal protective equipment (PPE) is based on qualitative professional judgment of the extent of fungal contamination (defined as minimal, moderate, or extensive), while USEPA guidance for mold remediation in schools is based on quantitative estimates of the total surface area affected (defined as small (less than 10 ft2), medium (between 10 and 100 ft2), or large (greater than 100 ft2)). The New York City guidelines differentiate between large isolated areas of contamination (30 to 100 ft2) and extensive contamination (greater than 100 contiguous ft2 in an area).

In general, however, the literature agrees on the point that a particular strategy or combination of strategies recommended for a given mold abatement effort (including the degree of worker protection needed) will depend on site-specific factors, such as the contaminating agent, the type of substrate that is contaminated (e.g., whether porous or non-porous), the extent of the contamination, the location of the site requiring remediation, and the presence of highly susceptible occupants. For example, slight fungal contamination of a semi-porous concrete floor may only require cleaning, while extensive mold growth in a carpet will require complete removal. Appropriate PPE and containment measures for situations of minimal colonization (small isolated surface area contamination) might include contaminated source containment to minimize dust or spore dispersion (e.g., dust suppression methods such as misting, covering with sticky sheeting or an encapsulant prior to removal) and the use of a N-95 disposable respirator and gloves for PPE. However, use of a N-95 respirator does not necessarily result in decreased exposure if there is not a proper fit. For remediation of moderate or large areas of mold growth, or where sensitive individuals are present in the home, containment of the source by enclosing the work area with a plastic sheet and sealing with tape and negative pressurization may be warranted. In many cases, the protection and mitigation methods most appropriate must be determined using professional judgment, and it is often recommended that investigators seek additional advice, when needed, from occupational physicians, respiratory protection experts, or health and safety professionals to select appropriate PPE.

Moisture Control

Because one of the most important factors affecting mold growth in homes is moisture level, controlling this factor is crucial in mold abatement strategies. Many simple measures can significantly control moisture, for example: maintaining indoor relative humidity at no greater than 50%-60% through the use of dehumidifiers, fixing water leakage problems, increasing ventilation in kitchens and bathrooms by using exhaust fans, venting clothes dryers to the outside, reducing the number of indoor plants, using air conditioning at times of high outdoor humidity, heating all rooms in the winter and adding heating to outside wall closets, sloping surrounding soil away from building foundations, fixing gutters and downspouts, and using a sump pump in basements prone to flooding. Vapor barriers, sump pumps, and above-ground vents can also be installed in crawlspaces to prevent moisture problems. A good description of the many issues in controlling moisture in buildings can be found in the Institute of Medicine's report, Damp Indoor Spaces and Health , particularly on how buildings get wet, in chapter 2, and barriers to dampness prevention and reduction and related public health approaches, in chapter 7. Numerous recommendations on managing moisture in and around a house are available in the HUD report, Durability by Design .

Removal and Cleaning of Mold Contaminated Materials

Non-porous (e.g., metals, glass, and hard plastics) and semi-porous (e.g., wood and concrete) materials contaminated with mold and that are still structurally sound can often be cleaned with detergent or bleach solutions or by using quaternary amine preparations; however, in some cases, the material may not be easily cleaned or may be so severely contaminated that it may have to be removed. Do not mix detergents and bleach. Some detergents have ammonia, which produces phosgene gas, a poisonous, suffocating gas, when mixed with bleach. It is recommended that porous materials (e.g., ceiling tiles, wallboards, and fabrics) that cannot be cleaned be removed and discarded. In severe cases, clean-up and repair of mold-contaminated buildings may be conducted using methods similar to those used for abatement of other hazardous substances such as asbestos. For example, in situations of extensive colonization (large surface areas greater than 100 ft2 or where the material is severely degraded), extreme precautions may be required, including: full containment (complete isolation of work area) with critical barriers (airlock and decontamination room) and negative pressurization, personnel trained to handle hazardous wastes, and the use of full-face respirators with HEPA filters, eye protection, and disposable full-body covering.

Physical removal interventions have proven effective, although additional research is needed regarding the containment of mold spores during the renovation process. In addition to strategies presented in the specific guidance documents listed above, an overview of the various recommended practices for the remediation of mold-contaminated materials, including porous, semi-porous and non-porous material removal, HVAC system remediation, containment strategies, and judging remediation effectiveness is presented in Bioaerosols: Assessment and Control .

The effect of biocides (to kill existing growth) and antimicrobials (to suppress or prevent growth) on mold varies according to mold species, and more research is needed to fully assess efficacy. The different chemical classes of biocides include alcohols, aldehydes, halogens, hydrogen peroxide, phenolics, and quaternary ammonium compounds. The use of biocides is discouraged by some experts, because little research has been conducted on their effectiveness for this use and because of the potential human health hazards associated with this use. In addition, research indicates that dead mold material often still retains the allergenic or toxic properties of the mold, and thus replacement is often cited as the best mitigation option.

Because of their potential to rapidly spread molds throughout a building, ventilation systems are of particular concern as mold contamination sources. It is possible to clean ducts made of bare sheet metal, and EPA recommends considering cleaning such ducts if substantial visible mold growth is present. Cleaning porous, insulated ducts is difficult, however. There are no registered biocides for treatment of such duct materials. Mechanical cleaning of such ducts has also been shown to be relatively ineffective. For example, a study investigating the effectiveness of mechanical cleaning of fibrous duct material contaminated with mold growth by vacuuming concluded that mechanical cleaning was only able to temporarily (for 6 weeks) reduce the surface mold load. EPA, the National Air Duct Cleaners Association, and the North American Insulation Manufacturers Association all recommend the replacement of wet or moldy fiberglass duct material.