Damp Indoor Spaces and Health (2004) / Chapter Skim
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2 Damp Buildings
2 Damp Buildings
Pages 29-89
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From page 29... ...
This chapter addresses those issues to the extent that present scientific knowledge allows. It starts with a description of how and where buildings become wet; reviews the signs of dampness, how dampness is measured, and what is known about its prevalence and characteristics, such as severity, location, and duration; discusses the risk factors for moisture problems; reviews how dampness influences indoor microbial growth and chemical emissions; catalogs the various agents that may be present in damp environments; and addresses the influence of building materials on microbial growth and emissions.
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From page 30... ...
It may represent visual observations of current or prior moisture (such as water stains or condensation on windows) , observed microbial growth, measurement of high moisture content of building materials, measurement of high relative humidity in the indoor air, moldy or musty odors, and other signs that can be associated with excess moisture in a building.
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From page 31... ...
If the air is cooled sufficiently, a portion of the gaseous water vapor in the air will condense, producing liquid water. The highest temperature that will result in condensation is called the "dewpoint temperature." "Humidity ratio" is another technical term used to characterize the moisture content of air.
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From page 32... ...
They cannot move about as freely as liquid water molecules or water vapor molecules and are in what is sometimes referred to as the adsorbed state. Water must accumulate on surfaces to a depth of four or five molecules before it begins to move freely as a liquid (Straube, 2001)
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From page 33... ...
Thus, the "best" leak is one that is large enough to be noticed right away but small enough that the wetting does not promote microbial growth or affect materials. Both floods and slow leaks can result in large areas of fungal growth.
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From page 34... ...
Several design approaches are available for preventing ice dams: • Air-seal and heavily insulate the top of the building so that escaping heat does not reach the roofing. • Ventilate the roof sheathing from underneath with outdoor air.
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Excessive moisture in foundations is often the result of poorly managed rainwater, but it may also result from groundwater intrusion, plumbing leaks, ventilation with hot humid air, or water in building materials (such as concrete) or in exposed soil (for example, saturated ground in a crawl space foundation)
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From page 36... ...
In fact, if the outdoor-air dewpoint is higher than the temperature in this space, ventilating air will add moisture to the cavity, not dry it and this can result in conditions favorable for microbial growth. A solution to this problem is to insulate the foundation wall on the outside.
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From page 37... ...
Most of the materials used in the pathway are moistureinsensitive -- able to withstand dampness without decomposing, dissolving, corroding, hydrolyzing, or supporting microbial growth. Moisture problems occur when water leaks from pipes or from sinks, tub or shower enclosures, washing machines, ice machines, or other fixtures and appliances that have water hookups.
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From page 38... ...
Such steps reduce, but do not eliminate, the possibility of microbial contamination. Construction Moisture In newly constructed buildings, a large amount of water vapor can be released by wet building materials such as recently cast concrete, and wet wooden products (Christian, 1994)
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From page 39... ...
The combination of high RH in indoor or outdoor air and cooled building materials increases the risk of dampness problems and microbial growth. Even without condensation, the local RH of air at the surface of cool material can be very high, leading to high moisture content in the material.
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From page 40... ...
Water vapor in this accidental outdoor airflow may condense on the backside of gypsum board or in cabinets that have holes for wire or plumbing. The backside of interior gypsum board and the underside of vinyl wallpaper on exterior walls are common locations for mold growth resulting from this process (Lstiburek, 2001)
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From page 41... ...
Water vapor in basements or crawl spaces may come from water passing through the foundation materials as liquid or vapor or from the ventilating air when outdoor-air dew points are high, or it may be dominated by water vapor from exposed soil (Kurnitski, 2000)
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From page 42... ...
office buildings found that dirty cooling coils, dirty or poorly draining drain pans, and standing water near outdoor air intakes were not associated with reports of mucus membrane symptoms, lower respiratory symptoms, or neurologic symptoms (Mendell and Cozen, 2002)
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Air leaving the cooling coils is often nearly saturated with water vapor, and the high humidity of this air increases the risk of microbial growth. HVAC systems sometimes have a humidifier that uses steam or an evaporation process to add moisture.
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The results suggest that limiting microbial contamination of HVAC systems may yield health benefits, and follow-up research is recommended. PREVALENCE, SEVERITY, LOCATION, AND DURATION OF BUILDING DAMPNESS Prevalence Table 2-1 provides examples of published data on the prevalence of signs of dampness in buildings.
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university Visible mold 5 students Visible mold or damp stains 12 45 Visible mold or damp stains or water damage 15 (continued on next page)
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TABLE 2-1 continued 46 Reference Country Population Dampness Metric Prevalence, % Nevalainen et al., 1998 Finland 450 private Inspections, surface moisture measurements, houses and questionnaire on previous or current damage Signs of moisture damage in roof 40 Signs of moisture damage in basement 25 Signs of moisture damage in walls 33 Plumbing-related moisture damage 25 Leakage from clothes washer or dishwasher 20 Leakage in ventilation ducts 20 Any of above 80 Norbäck et al., 1999 Sweden homes of 429 Questionnaire via interview subjects Water damage in last year 16 Floor dampness in last year 5 Visible mold in last year 9 Moldy odor in last year 6 Zock et al., 2002a 14 European 16,687 homes Questionnaire via interview countries, Water damage in last year 12 Australia, Water on basement floor in last year 2 India, New Mold or mildew in last year 22 Zealand, and United States Nonresidential buildings Jaakkola et al., 2002 Finland 932 adults Questionnaire about workplace who were Water damage in last year 6 controls in Damp stains or peeling paint in last year 12 asthma case- Visible mold in last year 3 control study Mendell and Cozen, 2002 United States 100 U.S. office Questionnaire buildings Past water damage in building 85 Current water damage in building 43 aIncludes data from Norbäck et al.
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(2003) have assessed the occurrence of moisture damage, fungi, and airborne bacteria in schools in Finland, focusing on the impact of main building frame material (wooden vs concrete or brick)
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They established associations between occupant-reported water damage, mold and mold odors, and objectively measured concentrations of viable indoor fungi in dust. However, they found little association between questionnaire responses and an objective measure of total airborne fungal matter (ergosterol concentration)
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From page 49... ...
Information on the prevalence or severity of moisture damage reported by occupants is likely to be highly subjective. The validity and reliability of data gathered from questionnaires are affected by several survey factors, such as sample size, response rate, recall period, and factors related to the design of the questionnaire.
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It should be remembered, however, that estimation of the size of damage is difficult and that estimation accuracy varies because damage is often hidden. Location Intuition suggests that the location of moisture damage or mold growth might be important in evaluating exposure because it will be related to the amount of pollutants that may come into contact with a person.
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From page 51... ...
"Ongoing damage" -- defined as damage resulting from either recent wetting or a lack of change in moisture conditions within 6 months of construction -- has been associated with higher concentrations of culturable fungi in building materials than "dry damage" -- past damage due to high moisture conditions where the materials had subsequently dried without remediation (Pasanen et al., 2000a)
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(1992) found that indoor viable mold propagules were weakly correlated with several risk factors for moisture problems (age of building, moisture-retaining building materials, and the presence of a crawl space)
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From page 53... ...
The entry of warm, humid outdoor air into ventilated crawl spaces, which are often cooler than outdoors, serves as a moisture source for the crawl spaces. Some codes, such as the 2000 International Residential Code, contain exceptions that provide a path to constructing sealed insulated crawl spaces (ICBO, 2000)
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From page 54... ...
The minimal moisture need for microbial growth may be characterized in terms of the water activity of the substrate, aw, which is the ratio of the moisture content of the material in question to the moisture content of the same material when it is saturated. In a situation where the material is in equilibrium with surrounding air that has a RH of 100%, aw = 1.
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From page 55... ...
Signs of microbial growth can thus be detected on many parts of a structure. Airborne spores and cells also accumulate in the parts of the structure that are in contact with soil or outdoor air, especially parts that act as sites of infiltration of intake air.
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From page 56... ...
This section focuses on fungi and bacteria associated with damp indoor spaces. Other microorganisms that may be found in such environments -- notably, house dust mites -- are not addressed here, although their presence may have important effects on occupants; the health effects of exposure to them and to others more generally related to indoor environments are covered in detail in the Institute of Medicine (IOM)
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From page 57... ...
This report, following the convention of much of the literature on indoor environments, uses the terms fungus and mold interchangeably to refer to the microorganisms. Filamentous fungi, yeasts, and bacteria are common in outdoor soil and vegetation, and outdoor air is an important transport route to the indoor environment for spores and other particles of microbial origin.
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Some studies have shown that increased airborne concentrations of fungi are associated with moisture damage in a building, and others have failed to show any such pattern. Taken together, the studies indicate that the fungal
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Environmental bacteria also grow in all wet spaces and are found in most cases where there is mold growth (Hyvärinen et al., 2002) , but the profile of bacterial genera and species growing on moist building materials differs from that originating from humans.
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60 DAMP INDOOR SPACES AND HEALTH TABLE 2-2 Summary of Studies of Airborne Fungal Concentrations in Residences in Relation to Building Dampness Characteristics Number and Study Type of Sites Study Design Methoda Gallup et al., 1987 127 Moisture problem 6-stage impactor residences Non-problem Hunter et al., 1988 62 Monitoring complaint 6-stage impactor residences home (MEA) Miller et al., 50 Characterize RCS (rose 1988 residences concentrations of bengal malt fungi and fungal extract)
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fungi associated with visible mold No mold: <38,600 cfu/m3 (MD 21–283) Indoors: <18,900 cfu/m3 High indoor:outdoor ratio and flora Outdoors: <1,090 cfu/m3 indicated indoor-air sources Damaged: 10–2,300 cfu/m3 Mean concentrations of viable fungi (GM 102)
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D) complaints + visible mold (18)
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No association between mean concentrations and visible mold; increased concentrations of fungi associated with musty odor, moisture or humidity, poor ventilation, and failure to clean indoor mold growth Before repairs: 860–1,300 cfu/m3 Local exhaust method most During repairs: <8 × 105 effective for control; personal protection still needed 37–7,619 cfu/m3 (MD 549) Higher concentrations in residences with visible mold Damaged: 1,993 to >7,069 cfu/m3 Higher concentrations in residence 1.8–6.6 × 10 5 spores/m3 with visible mold Control: 194–336 cfu/m 3 3.7–4.7 × 103 spores/m3 A)
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From page 64... ...
of the most prevalent species in indoor growth sites is generally different from that of species normally found in outdoor air, and otherwise unusual species may prevail indoors. Table 2-3 lists examples of fungal genera that have been isolated from "moldy" building materials or surfaces.
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From page 65... ...
Bacteria that have been identified in samples of moldy-building materials are shown in Table 2-5. Components of Microbial Agents Some studies of fungi and bacteria examine specific microbial components found in damp indoor environments.
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From page 66... ...
In the experimental study, the smaller particles were released in greater numbers than whole spores, but the concentrations of the small fragments in indoor environments have not yet been characterized. Their small size makes them capable of penetrating deeply into the alveolar region.
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From page 67... ...
Gram-negative bacteria are also common in house dust, soil, and plants, and they are probably carried indoors on pets and dust. Allergens of Microbial Origin Fungi produce an enormous array of potentially allergenic compounds; each fungus produces many allergens of different potencies.
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Peptidoglycans are the chemical substances that make up the rigid cell walls of eubacteria (bacteria with rigid cell walls, also called true bacteria)
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From page 69... ...
. However, most of them have sources in addition to microbial growth, so their occurrence is not specific for damp indoor environments with microbial growth.
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. Variable production of toxins while microorganisms are growing on building materials has been shown experimentally (Murtoniemi et al., 2002, 2003a,b; Ren et al., 1999b)
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. Some bacteria found in damp indoor environments are also capable of producing toxins.
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Building materials differ in the degree to which their constituents support microbial growth. Below are brief descriptions of the characteristics of some common materials that influence microbial growth.
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However, nutrients from water and air can accumulate on them and support microbial growth. Polyvinyl chloride (PVC)
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(2000) reviewed four case studies of health symptoms thought to be caused by chemicals that were emitted when high moisture content was combined with building materials that contained plasticizers.
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From page 75... ...
During the life span of a building, weather changes and other events cause at least temporary wetting of some of its parts; signs of microbial growth can thus be detected on many parts of a structure. Microbial growth is regulated by the available resources, conditions, and competing organisms.
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The committee's discussion of the public health response to damp indoor spaces (Chapter 7) provides additional observations on how some of the recommendations for actions might be accomplished.
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From page 77... ...
• Changes in building design, operation, maintenance, and use are the key to preventing the manifestation of dampness-related building damage and microbial growth. Recommendations • Precise, agreed-on definitions of dampness should be developed to allow important information to be gathered about mechanisms by which dampness and dampness-related effects and exposures affect occupant health.
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From page 78... ...
-- The microbial ecology of buildings, that is, the link between dampness, different building materials, microbial growth, and microbial interactions. -- The impact of the duration of moisture damage on materials and its possible influence on occupant health.
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From page 79... ...
1993. Microbial growth in spray humidifiers of health facilities.
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2002. Occurrence of toxigenic Aspergillus versicolor isolates and sterigmatocytins in carpet dust from damp indoor environments.
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2001. Microbial growth in indoor environments.
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2002. Fungi and actinobacteria in moisture-damaged building materials -- concentrations and diversity.
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2000. Humidity control in outdoor-air-ventilated crawl spaces in cold climate by means of ventilation, ground covers and dehumidification.
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2002. Effect of liner and core materials of plasterboard on microbial growth, spore-induced inflammatory responses and cytotoxicity in macrophages.
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2000a. Fungal growth and survival in building materials under fluctuating moisture and temperature conditions.
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2000b. The relationship between measured moisture conditions and fungal concentrations in water damaged building materials.
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1994. Health implications of fungi in indoor environments.
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2000. Mycotoxins in crude building materials from water-damaged buildings.
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2001. Nasal lavage biomarkers: effect of water damage and microbial growth in an office building.
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