Building Envelope, Moisture Management, and Health
The foundation, walls, windows, and roof of a building make up an “envelope” intended to shelter people and equipment from the weather, and from natural and man-made hazards. Windows and doors allow outside air, light, people, equipment, and supplies to enter or exit a building. Skylights allow in daylight. Building envelopes can be designed for natural ventilation or for mechanically conditioned air or hybrid systems. Whether planned or not, buildings have openings that allow the penetration and internal movement of air, water, and contaminants.
Typically, guidelines for green schools address building envelope issues concerning siting, glazing, natural ventilation, and materials. Typically, the conservation of water, both outside and inside the building, is addressed through landscaping-related efforts such as irrigation, and plumbing-related features, such as restrooms. Existing guidelines are silent for the most part about building envelope per se except in reference to roofs and sound attenuation of outside noise. The committee believes that the design, construction, and maintenance of the building envelope are critical to green schools and therefore should have a more prominent place in any set of green school guidelines, for the reasons outlined below.
BUILDING ENVELOPE AND MOISTURE MANAGEMENT
It is popularly thought that green buildings are those buildings that are constructed using specific materials, systems, and technologies. However, it may not be as obvious that “dry” is a primary design objective for a green school building. Moisture ranks as a leading cause of structural damage, and excess moisture in a building has been associated with a variety of health problems in children and adults (IOM, 2004).
Water-related issues in buildings originate from many sources: groundwater, plumbing failures, construction materials, occupants, and the external environment. As long as a building is properly designed, sited, constructed, operated, and maintained, water can be managed effectively. However, excess water or moisture in a building can lead to structural failures and health-related problems when materials stay wet long enough for microbial growth, physical deterioration, or chemical reactions to occur (IOM, 2004). A complex set of moisture-transport processes related to climate, building design, construction, operation, and maintenance determine whether a building will have a moisture problem that could influence the health of the occupants.
Well-designed moisture control considers the potential damage and degree of risk associated with each of the following four transport mechanisms (from most to least potent):
Air transport, and
Bulk transport, or leakage of rain, melting snow, and groundwater through the building envelope, is orders of magnitude more destructive than any other force. Capillary movement of water from the outside of the building into the building through porous surfaces and the movement of air-transported water vapor are second and third in the rank order of transport mechanisms. Both represent a significant threat and require dedicated attention during design and construction. Vapor diffusion is a relatively weak force but also requires careful detailing and execution of building assemblies. Excellent resources for proper moisture control design include The Moisture Control Handbook, Principles and Practices for Residential and Small Commercial Buildings by Joseph Lstiburek and John Carmody (1994) and The Building Foundation Design Handbook (ORNL, 1988).
EXCESSIVE MOISTURE AND HEALTH
Recently there has been concern that indoor moisture “dampness” and mold growth can lead to a variety of health problems in adults and children. The most consistent and convincing associations relate to respiratory disease, especially asthma. Asthma is a disorder of airflow obstruction. People with asthma are subject to episodic wheezing, coughing, and shortness of breath. Although these symptoms are common clinical features of asthma, they are common symptoms of other respiratory illnesses as well. Finding a widely accepted definition of this disease has proved problematic, and the following has been offered as the most acceptable:
Asthma is understood to be a chronic disease of the airways characterized by an inflammatory response involving many cell types. Both genetic and environmental factors appear to play important roles in the initiation and continuation of the inflammation. Although the inflammatory response may vary from one patient to another, the symptoms are often episodic and usually include wheezing, breathlessness, chest tightness, and coughing. Symptoms may occur at any time of the day, but are more commonly seen at night. These symptoms are associated with widespread airflow obstruction that is at least partially reversible with pharmacologic agent or time. Many persons with asthma also have varying degrees of bronchial hyperresponsiveness. Research has shown that after long periods of time this inflammation may cause a gradual alteration or remodeling of the architecture of the lungs that cannot be reversed with therapy. (IOM, 2000, pp. 23-24)
Asthma affects 8 percent to 10 percent of the population and even larger proportions of children in certain cities or poor urban populations. It is a common reason that children are absent from school and one of the most common causes of work absences as well; 14 million days of school loss were recorded in 1994-1996, 3.4 days per child with asthma (Cox-Ganser et al., 2005).
Indoor environments are an important factor in chronic asthma symptoms and morbidity, whether these environments are in the home or in the school. The Institute of
Medicine (IOM) has issued two reports on the association of excessive moisture or “dampness,” mold growth, and respiratory illness in building occupants, Clearing the Air: Asthma and Indoor Air Exposures (IOM, 2000) and Damp Indoor Spaces and Health (IOM, 2004). Both concluded that damp, moldy buildings were associated with respiratory symptoms both in people with asthma and in the general population. To the extent that they might affect indoor dampness, green school designs might affect students’ health and productivity. If school buildings can be designed to minimize the contribution to asthma morbidity, they can have a positive impact on health and performance.
The report Damp Indoor Spaces and Health considered separately the common respiratory symptoms (wheeze, cough, shortness of breath) and the diagnosis of asthma (usually based on reported physician diagnosis, reversible obstruction measured by lung function tests, or use of appropriate medication by the respondent). In addition, the report distinguished asthma development (the appearance of asthma for the first time) from asthma exacerbations (asthma symptoms in persons with a diagnosis of chronic asthma).
Using the National Academies’ hierarchy of evidence for scientific inference (see Box 1.1), the report found sufficient evidence of an association between indoor dampness and several respiratory health outcomes, although the evidence was not strong enough to say there was a causal relationship. In the case of asthma, the association was found in people with asthma in general.
There are at least two distinct variants of asthma: an extrinsic, allergic variant that occurs in the context of immunoglobulin E (IgE)-mediated sensitization to environmental allergens and an intrinsic, nonallergic variant with no detectable sensitization and low IgE concentrations. In both variants, the airways are strikingly hyperresponsive, and symptoms may also be mediated by irritant responses. In those studies that evaluated asthmatic patients for IgE-mediated sensitization, the association was stronger in sensitized individuals; thus the IOM study concluded that the association was strongest in sensitized individuals. In addition, an association between dampness and mold and the symptoms of cough or wheeze was consistently found in studies of the general population. Because asthma has been diagnosed in only 8 percent to 10 percent of the population, it was unlikely that this relationship could be accounted for in these studies by asthma alone. Thus, the 2004 IOM study concluded that moisture and mold were associated with cough and wheeze in the general population.
The existing evidence was considered to be insufficient to support an association between dampness and mold and asthma development because fewer studies were available. Of the 10 studies available, only 1 (Jaakola et al., 2002) found that the association was insignificant. The others found an association with moisture, mold, or both. Particularly important were the three birth cohort studies (Belanger et al., 2003; Slezak et al., 1998; Maier et al., 1997) in which infants and children who were genetically at risk to develop asthma were observed for several years. Stark et al. (2003) reported on a birth cohort of 849 infants less than 1 year old who had at least one sibling with physician-diagnosed asthma; they found that wheeze and persistent cough were associated with measured airborne concentrations of Penicillium and Cladosporium, two types of mold commonly found in indoor air samples.
Finally, upper respiratory symptoms (nasal congestion, sneezing, runny or itchy nose) were associated with damp indoor environments and mold. Like asthma, chronic rhinitis has an allergic and a nonallergic variant. The allergic variant occurs in the context of IgE-mediated sensitization to environmental allergens. In the studies included in the 2004 IOM
report, upper respiratory symptoms were associated with dampness and mold in persons with self-identified allergic rhinitis, as well as in the general population. Other studies reported that the frequency of “colds,” that is, acute viral infectious rhinitis, was associated with dampness and mold. Because the cause of upper respiratory symptoms could not be identified, the committee concluded that the symptoms, but not a specific illness, were associated.
The mechanisms by which damp indoor spaces and mold are associated with respiratory illness are not clear, but there are several possibilities. First, many people with asthma demonstrate IgE-mediated sensitization to mold, so the possibility exists that symptoms are related to specific immune mechanisms. Mold produces a number of materials such as peptidoglycans and polysaccharides that induce inflammation through the innate immune pathways; other materials such as volatile organic compounds3 and toxins may have direct effects because asthmatic airways have a characteristic hyperresponsiveness and are excessively responsive to exposures to irritants. Other organisms such as gram-negative or gram-positive bacteria might coexist with mold in damp environments; endotoxin or lipoteichoic acid from these organisms might induce airway symptoms. Finally, the interaction of moisture and mold with building materials may produce metabolites that have direct irritant effects on asthmatic airways. The multiplicity of possible mechanisms illustrates that the pathways to respiratory effects will be complex, but all of these mechanisms are plausible consequences of excessive indoor moisture. Maintaining structures that are dry (i.e., without excessive moisture) potentially could prevent all of these effects.
The findings of key relevance to this interim report from Damp Indoor Spaces and Health are summarized in Box 2.1.
Sufficient Evidence of an Association Between Dampness and Respiratory Health
Limited or Suggestive Evidence of an Association
Sufficient Evidence of an Association Between Mold or Other Agents and Respiratory Health
Limited or Suggestive Evidence of an Association
SOURCE: IOM, 2004.
In addition to potential health benefits, designing for effective moisture management will likely have benefits for the building as well. The more durable a building is, the longer its components will last (Deal et al., 1998). The materials in long-lived building assemblies are replaced less frequently than in nondurable structures. This makes dry structures resource and energy efficient, because new replacement materials are not harvested, mined, and produced, nor is energy used to make, transport, and assemble the replacement components. Dry buildings also require fewer resources and money to repair and maintain. For example, damp surfaces cause stains and peeling paint that require frequent repainting and cleaning. For these reasons, dry buildings may have lower life-cycle costs associated with them.
FINDINGS AND RECOMMENDATION
Finding 2: In regard to issues related to building envelope, moisture management, and health, the committee has found the following:
There is sufficient evidence to establish an association between moisture problems in buildings (floods, visible dampness, leaks, mold growth in spaces or in heating, ventilation, and air-conditioning [HVAC] systems) and adverse health outcomes, particularly asthma and respiratory symptoms, among children and adults.
Excessive moisture in a building can lead to structural damage, deterioration of the performance of building systems and components, and cosmetic damage, all of which can result in increased maintenance and repair costs.
Guidelines for green schools typically do not adequately address the design detailing, construction, and long-term maintenance of building envelopes to ensure that allergen sources are controlled, moisture is controlled, and a building is kept dry over the long term.
Well-designed, constructed, and maintained building envelopes are critical to the control and prevention of the excessive moisture and molds that have been associated with adverse health effects in children and adults. Designing for effective moisture management will likely have benefits for the building, including lower life-cycle costs. Excellent resources for proper moisture control design include The Moisture Control Handbook, Principles and Practices for Residential and Small Commercial Buildings by Joseph Lstiburek and John Carmody (1994) and The Building Foundation Design Handbook (ORNL, 1988).
Recommendation 1: The control of excessive moisture, dampness, and molds to protect the health of children and adults in schools and to protect the structural integrity of a building should be a key objective for green schools. MASSTECH should develop guidelines that specifically address moisture control as it relates to the design, construction, operation, and maintenance of a school building’s envelope (foundations, walls, windows, and roofs) and ventilation systems, and related items such as siting, landscaping, and plumbing systems.