TECHNICAL #1504 RESOURCE SHEET

Frequently Asked Questions About Mold

The presence of unwanted or excessive moisture in buildings can lead to structural performance problems, as well as concerns about possible health risks. One area of concern is mold and mildew growth. Homeowners, builders, and contractors can benefit from having accurate, fact-based information on mold, mildew, and wood decay fungi.

Q: What is mold? is often presented by the media as the A: Mold and/or mildew are microscopic fungi main driving force for the current increase that are present virtually everywhere, in moisture/mold claims. However, mold indoors and outdoors. They grow on a needs moisture to grow and moisture can variety of organic materials, including wood come from multiple sources in a house, products(1)(2). many of which have nothing to do with the amount of fresh air exchange a building Q: How do molds enter an indoor experiences. A leaky foundation wall or environment and how do they grow? a chronic plumbing leak releasing water A: Molds may be present in outdoor or indoor onto drywall are two examples. There can air. Mold spores from the outside may be cases where the humidity level in a enter a house through open doorways and house would be lower with more fresh air, windows, or though heating, ventilation, potentially alleviating some moisture/mold and air-conditioning systems. Spores in problems, but to characterize this as the the outside air also attach themselves root cause of mold problems is incorrect(6). to people and animals, making clothing, shoes, bags, and pets convenient vehicles Q: Why is mold a concern? for carrying mold indoors(3). A: Mold and/or mildew fungi do not cause Unlike decay-producing fungi, ­decay; however, the environment that mold and mildew alone do not Mold needs oxygen, water, nutrients, and a ­fosters mold growth will also support cause significant loss in the temperature between 40 degrees and 100 decay-producing organisms(10). Addition- strength of wood products. degrees Fahrenheit to grow(4). Mold spores ally, mold produces spores, which often can grow when they come into contact with become airborne and may create allergic a food source where there is excessive reactions in some people(4). moisture, such as where there are leaks in roofs, pipes, walls, or plant pots, or where Q: A house has a water leak. What is there has been flooding. Additionally, an the potential for growing mold in the average relative humidity of 80% or more leak area? over a month's duration will provide suf- A: Materials that are exposed to a constant ficient moisture for mold growth(5). Many leak or have been soaked and not dried organic materials (e.g., wet cellulose mate- thoroughly can support mold growth. Some rials, including paper and paper products, molds can form a new colony in one or cardboard, ceiling tiles, wood, and wood two days on damp materials. Molds do products) provide suitable nutrients to sup- not require light and can continue growing port mold growth. Inorganic materials such indefinitely without light(7). as dust, paints, wallpaper, insulation mate- rials, drywall, carpet, fabric, and upholstery Q: What about moisture in the crawl space? can also support mold growth(3). A: There is no definitive answer regarding moisture problems in the crawl space. Q: Is mold occurring because buildings are A symposium on the subject held by the now "air tight"? American Society of Heating, Refrigeration, A: This rationale for moisture/mold problems and Air-Conditioning Engineers produced Frequently Asked Questions About Mold

the following recommendations(8): to check a building's compliance with taken in a unique situation cannot be • There should be proper drainage, ­federal mold standards(1). Testing for mold interpreted without physical inspection ­clearance, and access. is also difficult because mold is every- of the contaminated area or without • Crawl spaces should have ground covers where, and therefore, testing will not prove considering the building's characteristics for moisture control. These should be in- that a house is free of mold(6). The U.S. and the factors that led to the present stalled to limit evaporation from the soil. Centers for Disease Control and Prevention condition(3). • Heated crawl spaces should not be (CDC) advises that it is not practical to test vented with outdoor air. for mold growth in a house because large Q: How do you determine whether a mold • Unheated crawl spaces may be vented, mold infestations can usually be seen is "toxic"? but there is no overriding need to do or smelled(3). When testing is done, it is A: Unfortunately, it is impossible for home- so for reasons of moisture control if usually to compare levels of mold spores owners to distinguish between so-called an effective ground cover is present. inside the house with levels outside the "toxic" and "non-toxic" molds because they (Note: check with local building codes to house(7). all look like black or gray sooty patches. verify whether this practice is permitted Press coverage about lawsuits and health in your jurisdiction.) A thorough inspection of a house, to check studies involving mold has focused on for signs of moisture problems or active one type of mold called Stachybotrys Q: With wood, at what moisture content mold growth, is likely to be more effective ­chartarum, which is often referred to as does mold become a concern? than testing as a way to size up potential "the toxic mold." However, there is no A: A moisture content greater than 19% is problems(6). It is usually not necessary to particular reason why this mold should be sufficient to support mold growth. This identify the species of mold growing in a singled out, as all molds should be treated moisture content is also sufficient to sup- residence, and CDC does not recommend with caution(4). port decay-producing organisms(9), which, routine sampling for molds. unlike mold, can cause permanent loss of Q: What is Stachybotrys chartarum structural strength(10). Wood can achieve Current evidence indicates that ­allergies (Stachybotrys atra) and what should this moisture content when exposed to are the health problems most often people do if they determine it is present direct wetting from any source of moisture, ­associated with molds, and because the in their buildings or homes? or from extended exposure to an appro- susceptibility of individuals varies greatly A: Stachybotrys chartarum (also known as priate combination of high humidity and depending on the amount or type of mold, Stachybotrys atra) is a greenish-black temperature. sampling and culturing would not be mold. It can grow on material with a high ­reliable in determining the health risk. CDC cellulose and low nitrogen content, such Q: Do structural adhesives cause mold to recommends that if the occupants are as fiberboard, gypsum board, paper, dust, grow more readily? susceptible to mold and mold is seen or and lint. However, it is not necessary to A: A recent study on fungal susceptibility of smelled indoors, there is a potential health determine what type of mold may be pres- pine and aspen oriented strand board risk and the homeowner should arrange ent—all molds should be treated the same (OSB) found that the amount of mold for mold removal(3). with respect to potential health risks and growth on both OSB types was approxi- removal(3), including (per the CDC) Stachy- mately equal to the mold growth on solid Q: If a qualified environmental lab took botrys chartarum. Mold growing in homes aspen(11). These results indicate that the samples of the mold inside a home and and buildings, whether it is Stachybotrys adhesive in OSB has little or no effect returned the results, can CDC or anyone chartarum or other molds, indicates that on mold growth. Additionally, molds grow else interpret these results? there is a problem with water or moisture best on sources with freely available A: Standards for judging acceptable, that needs to be addressed. ­nutrients(12), and since the cured resins tolerable, or normal quantities of mold used in structural adhesives are a poor have not been established. If the home- Q: How common is mold, including source of freely available nutrients, these owner decides to pay for environmental Stachybotrys chartarum, in buildings? adhesives are generally not associated sampling for molds, CDC recommends that A: Molds are very common in buildings and with mold growth. the following items be addressed before homes and will grow anywhere there is the work starts: moisture. The most common indoor molds Q: If someone thinks they have mold in their • Who will establish the criteria for are Cladosporium, Penicillium, house, should they test for it? interpreting the test results? Aspergillus, and Alternaria. The scientific A: According to the EPA, sampling is • What are their qualifications? community does not have accurate infor- unnecessary in most cases where visible • What will be done, or what mation about how often Stachybotrys char- mold growth is present. Since no EPA or recommendations will be made based tarum is found in buildings and homes. It other federal limits have been set for mold on the sampling results? is less common than other mold species; or mold spores, sampling cannot be used Keep in mind that the results of samples however, it is not considered rare(3).

Frequently Asked Questions About Mold 2 Technical Resource Sheet 1504 | August 2018 Frequently Asked Questions About Mold

Q: Will mold affect the structural integrity of is present. Indoor mold growth can and it breaks just above the blade like a carrot the wood in my home? should be prevented or controlled by snapping in half, it is decayed(15). See A: Surface mold on wood from short-term controlling moisture indoors. If there is Figure 1 below. wetting does not structurally damage the mold growth in a home, the mold must wood(6). Mold and mildew are a different be cleaned up and the moisture problem Q: The homeowner has identified mold type of fungi than those that cause wood fixed. If the mold is cleaned up, but the growth and fixed the moisture problem. to rot. Unlike decay-producing fungi, mold moisture problem remains, then the mold Now, how do they clean up the mold? and mildew alone do not cause significant will probably return(1). A: A detergent and water solution(1) loss in the strength of wood products. ­(recommended by the EPA) or a bleach-to- Nonetheless, mold and mildew on wood Q: How do I determine if a product has been water solution (1 cup bleach per 1 gallon indicate high moisture, and prolonged damaged beyond cleaning? water as recommended by the CDC)(3) is periods of high moisture may also support A: In an initial assessment, the key ­question suggested to clean mold and kill fungi. The the growth of decay-producing fungi. This is: Does this appear to be a "mold only" detergent/water solution is often recom- is one of the reasons why it is important to condition, or does it appear to have mended because it has less potential than prevent the growth of mold and mildew(13). become a potential decay situation? Mold the bleach/water solution to be used in and mildew cause no structural damage to an unsafe manner. This cleaning process Q: How can mold growth be prevented? wood other than unsightly discoloration(10). will not prevent future growth—only an A: Controlling moisture is the most Mold growing on solid lumber or other environmental change (i.e., eliminating important part of mold-growth preven- structural wood products is most likely a the moisture) can prevent future mold tion. Mold will not grow if moisture is not surface contamination issue, not a struc- growth. The CDC recommends that large present. A properly constructed building is tural issue, so it can be cleaned, dried, and mold infestations should be addressed by designed to keep the inside of it dry, which used. However, if there is any evidence of a professional who has experience with prevents mold growth(1)(7)(10). As part of decay, the product should be replaced(14). cleaning mold in buildings and homes(3). routine maintenance, buildings should be Conversely, porous materials that are inspected for evidence of water damage moldy, such as ceiling tiles, sheetrock, and Q: Does cleaning have any negative and visible mold, and any conditions that carpet should be discarded(13). effect on the structural performance of could cause mold (such as water leaks, engineered wood products? condensation, infiltration, or flooding) If the wood is badly decayed, this will be A: Mold cleaning procedures recommended should be corrected(3). quite visible. Two common visual results of by the EPA or CDC (i.e., scrubbing with a decay are a bleached and stringy appear- detergent and water solution or ­scrubbing Specific Recommendations from CDC: ance to the wood, or a darkened surface with a dilute bleach solution) will not • Keep the overall humidity level in the with cubical cracking. If fungal growth degrade the structural characteristics of house below 50%. This 50% threshold is visible on the surface, the wood has engineered wood products. is often recommended to minimize probably suffered strength loss, but do localized conditions of relative humidity not rely on visual cues alone. Wood can If a remediator wishes to use another type greater than the commonly referenced appear stained and be sound, or can ap- of cleaning solution, he or she should be threshold of 80% that supports active pear normal yet still have already suffered asked to provide documentation that the mold growth. significant strength loss from decay. Use solution is not detrimental to wood-based • Use an air conditioner or a dehumidifier the pick test to determine whether or not products. If the information is not avail- during humid months. the wood is sound: Insert the point of a able, request a copy of the MSDS (Material • Be sure the home has adequate knife at a shallow angle to the surface Safety Data Sheet) for the product and ventilation, including exhaust fans in and attempt to lever up a thin splinter. If contact Weyerhaeuser engineering for the kitchen and bathrooms. the wood splinters, it is sound. If instead further advice. • Use paints that contain mold inhibitors. • Clean bathrooms with mold-killing Figure 1: products. • Do not carpet bathrooms. • Remove and replace flooded carpets.

Q: How do you get rid of existing mold? A: It is impossible to get rid of all mold and mold spores indoors; some mold spores will always be found floating through the air and settling with house dust. However, mold spores will not grow unless ­moisture Pick test on sound wood — splintering break Pick test on decayed wood — brash break Graphics reproduced with the permission of FPInnovations.(15)

Frequently Asked Questions About Mold 3 Technical Resource Sheet 1504 | August 2018 Frequently Asked Questions About Mold

Q: "Toxic" mold has attracted a lot of media conditions such as pulmonary hemor- pulmonary disorder or asthma) may attention. Should a homeowner be rhage or memory loss. These case reports experience difficulty breathing when concerned about possible health risks? are rare, and a causal link between the exposed to mold. Individuals with immune A: The CDC provides the following answer to presence of the toxic mold and these ­suppression may be at increased risk this question: “The hazards presented by conditions has not been proven.”(3) A for infection from molds. If the home- molds that may contain mycotoxins should common-sense approach should be used owner or any family members have these be considered the same as other common for any mold contamination existing inside ­conditions, a qualified medical clinician molds that can grow in [a] house. There is buildings and homes. should be consulted for diagnosis and always a little mold everywhere—in the air treatment. For the most part, one should and on many surfaces. There are very few The common health concerns from molds take routine measures to prevent mold case reports that toxic molds (those include hay-fever-like allergic symptoms. growth in the home.(3) containing certain mycotoxins) inside Certain individuals with chronic ­respiratory homes can cause unique or rare health disease (such as chronic obstructive

Links to More Information References • Canadian Wood Council and FPInnovations have collaborated on a website addressing 1. U.S. Environmental Protection Agency. 2010. A Brief the durability of wood, with a section specifically addressing mold. Guide to Mold, Moisture, and Your Home. cwc.ca 2.  California Dept. of Health Services. 2001. Mold in My Home: What Do I Do? • U.S. Centers for Disease Control and Prevention has developed a Q&A covering mold 3.  CDC Centers for Disease Control and Prevention. Facts related topics. about Stachybotrys Chartarum and Other Molds. cdc.gov/mold/basics.htm cdc.gov/mold/stachy.htm 4. NAHB Research Center's ToolBase Services. 2002. • U.S. Environmental Protection Agency covers issues, including cleanup, health concerns, Mold in Residential Buildings. and air quality, in A Brief Guide to Mold, Moisture, and Your Home. 5. International Energy Agency. 1990. Annex 14: epa.gov/mold/brief-guide-mold-moisture-and-your-home Condensation and Energy, Vol. 2: Guidelines and Practice. • USDA Forest Service, Forest Products Laboratory has a few documents related to 6. NAHB Research Center's ToolBase Services. 2002. moisture in homes. The most notable are Recognize, Remove, and Remediate Mold and Helping Your Buyers Understand Mold During the Mildew and Mold and Mildew on Wood: Causes and Treatment. Building Process. fpl.fs.fed.us/documnts/pdf2001/claus01b.pdf and 7. Bode M, Munson D. 1995. Controlling Mold Growth in fpl.fs.fed.us/documnts/techline/ii-4.pdf the Home. Kansas State University. 8. Rose W, TenWolde A. 1994. Recommended Practices • APA – The Engineered Wood Association's informational flyer briefly covers cleanup and for Controlling Moisture in Crawl Spaces. Issues in prevention of mold and moisture problems. Their Q&A section also has one entry dealing Crawl Space Design and Construction-A Symposium with mold. Summary. ASHRAE Technical Bulletin 88192, ASHRAE. apawood.org 9. Kirby S, Wiggins C. 1998. Moisture Control and Prevention Guide. NC State University. • American Wood Council (AWC) offers facts about how and when mold might start to grow 10. Clausen C. 2000. Recognize, Remove, and in or around your home. Remediate Mold and Mildew. Proceedings of 2nd awc.org/faqs/materials Annual Conference on ­Durability and Disaster Mitigation in Wood-Frame Housing. • Kansas State University. Although published in 1995, this document contains excellent 11. Laks P et al. 2002. Fungal Susceptibility of Interior information relating to the identification of mold in the home, preventative measures, Commercial Building Panels. Forest Products Journal and a highly detailed section on cleanup. Vol. 52(5);41-44. water-research.net/Waterlibrary/Mold/moldinhome.pdf 12. Forintek Canada Corp. and University of British Columbia School of Occupational and Environmental • New York City Health Department publishes Facts About Mold, a fact sheet with Hygiene. 2001. Discolorations on Wood Products: questions and answers about health concerns, healthy homes, and cleanup information. Causes and Implications. www1.nyc.gov/assets/doh/downloads/pdf/epi/mold-brochure.pdf 13. APA - The Engineered Wood Association. 2001. Mold and Mildew. • American Phytopathological Society publishes Stachybotrys chartarum: The Toxic 14. Yost N, et al. 2002. What You Need to Know About Indoor Mold. Mold. Building Science Corporation. apsnet.org/publications/apsnetfeatures/Pages/Stachybotrys.aspx 15. Canadian Wood Council and FPInnovations. Website on the durability of wood products. • Building Science Corporation, a private consulting firm that specializes in preventing and cwc.ca resolving problems related to building design, construction, and operation, has written a few documents relating to mold. Topics covered include testing, basic mold Q&A, cleanup, and designing for moisture. buildingscience.com/document-search

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