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MOISTURE MANAGEMENT
High Indoor Air Quality is Crucial in Schools and Health Care Facilities

Indoor Air Quality, or IAQ, is a hot topic in modern-day building and design, as it affects both the structure and the people inside it. Attaining high IAQ in new construction and retrofitting involves the control of problematic factors, such as mold and microbial growth, which may harm the building or its occupants, by causing respiratory diseases, such as asthma. According to the American College of Allergy, Asthma & Immunology, 50 percent of all illnesses are either caused or aggravated by poor IAQ.

Poor IAQ becomes a more serious matter of concern, however, when the structure in question is a school occupied by young students or a health care facility. Since their lungs are still developing, children are very vulnerable to mold-related illnesses, as are patients in hospitals, whose lungs are often weakened by sickness or age. Recent U.S. Department of Education research showed that about 20 percent of schools throughout the nation have problems linked to poor IAQ.


The steel stud cavity assembly is the most
common commercial wall construction.

If IAQ problems in existing buildings are not attended to, they can lead to Sick Building Syndrome (SBS), a condition where a building’s IAQ hits such poor levels that the intended use of the building becomes impaired or impossible. Many such facilities, including office buildings, schools and nursing homes, have been abandoned or demolished altogether because of the health threats to occupants. Airborne molds and fungus spawned by overly damp conditions within a building are a leading cause of SBS. Another cause is the emission of volatile organic compounds (VOC) from building products to chemical cleaners and interior furnishings. VOCs are gases or vapors given off by solids and liquids that often have short- and long-term adverse health effects. If building designs lack adequate ventilation, hazardous airborne chemicals on the interior may become trapped inside.

Fortunately, all of these conditions are avoidable. When managing a school or health care facility, it is important to understand IAQ and how to ensure the purity of interior air. The best way to do to this is through moisture management and proper ventilation strategies.

Moisture: Mold’s Best Friend
IAQ first became a national problem after the energy crisis of the 1970s inspired the design of airtight buildings to prevent the leakage of conditioned interior air. Though tight construction seals off the escape of conditioned air, it also traps water vapor inside the structure.

If not allowed to escape the building, water vapor condenses and saturates components of certain parts of the building, usually in areas outside of public view, such as inside the wall assembly.

Moisture in the Wall Assembly
Extended moisture exposure inside the wall assembly has a negative impact on its components. For example, wet insulation loses R-value, compromising the building’s energy efficiency. Moisture exposure also causes wood studs to deteriorate and break down and metal studs to corrode. But, the biggest moisture-related threat to IAQ is mold growth.

Mold can form and grow on any surface that provides a food source surrounded by moderate temperatures, oxygen and sufficient moisture. The best examples of mold food sources are cellulose-based substances. In today’s buildings, food sources for mold are readily available in the form of untreated paperfaced gypsum board, wood wall studs and wood-based sheathings. Once moisture is exposed to the mold food source, longdormant mold spores can gain a foothold. As long as the food and moisture sources are supplied, the mold colonies will continue to grow and prosper.

Moisture in the HVAC System
Water vapor—and the resulting mold and microbial growth—is also a problem in HVAC systems, especially those with uninsulated sheet metal ductwork. This moisture often arises from condensation caused by the changing temperatures of different seasons. During the summer, as cold air travels through warm uninsulated ducts, it causes beads of moisture to form on the interior or exterior of the ducts. And, during winter, heated air does the same as it travels through cold ducts. Condensation will occur on any duct surface where the temperature is either equal to—or lower than—the dew point temperature. The IAQ concerns begin, however, when this condensed moisture mixes with dust or dirt present in uninsulated ducts to spawn mold and microbial growth, which, in turn, can pollute the air supply of the building. If the condensation is left untreated, this mold and microbial growth will continue to worsen, leading to contaminated interior air.

HVAC systems have often been referred to as the “lungs of a building,” as they essentially perform the structure’s breathing, ventilating stale or contaminated air from a space and replacing it with fresh conditioned air, similar to the inhaling and exhaling functions of lungs. As with lungs, it is important to keep the inside of the HVAC system’s ductwork clean and free of impurities. The HVAC system is responsible for distributing air throughout the whole building, so any mold spores and other impurities, found in the ductwork will become part of the interior air the occupants breathe.

To prevent moisture and mold problems from occurring in schools and health care facilities, it is crucial for facility managers to be aware of the components that comprise successful moisture management strategies and request such components during the design process.

Moisture Management in Wall Assemblies
When fortifying a building’s defense against moisture, choosing the proper wall materials is a good place to start. The and public buildings is the steel stud cavity, which would typically include a masonry facade. Here are some guidelines on the contents of a steel stud cavity assembly: First, always use a water-resistive barrier (WRB)—it is the first line of defense against rainwater intrusion. Water will enter somewhere, somehow, so use a ventilation and drainage space between the masonry facade and the WRB. It is important to maximize condensation control in several ways—first, by using insulating sheathings. Use exterior air/wind barriers, since air can transport considerable moisture into assemblies, if not blocked. Use interior air barriers to help control wintertime moisture from migrating and condensing on cold surfaces. Next, include fiberglass insulation and a smart vapor retarder to not only control the wintertime moisture but also allow assemblies to dry during other seasons. And, in areas of the building that are moisture-prone, it is a good idea to install moisture-resistant treated gypsum boards in the interior walls instead of standard paper-faced gypsum board.

Fiberglass Insulation
When exposed to moisture, fiberglass insulation neither absorbs nor holds water. It is also resistant to mold and microbial growth, making it an excellent insulation choice in moisture-managing wall assembly designs.

Smart Vapor Retarders
Originally developed, tested and commercialized in Europe, smart vapor retarders resemble polyethylene film, but are actually polyamide, a nylonbased material. Polyamide film retards moisture under dry conditions, but if relative humidity in the wall cavity increases above 60 percent, they dramatically open up to a much higher permeance, which allows drying toward the interior of the building. In summer, when the air is humid, the moisture penetrates through the pores into the building interior, allowing building materials to dry out. If the relative humidity decreases, the pores close up again and the membrane then acts as a retarder to moisture. In the winter, this vapor retarder protects the building materials behind the membrane from condensation. Field tests have proven that smart vapor retarders effectively reduce the risk of moisture damage in the building envelope by increasing the construction’s tolerance to moisture load.

Moisture- & Mold-Resistant Gypsum Board
Traditional gypsum board is paperfaced and therefore, a potential mold food source in moisture-heavy conditions. An explosion of mold litigation cases over the past 10 years across the United States provided the gypsum industry an opportunity to assist in solving a growing public concern by concentrating their research programs into developing solutions—new moistureand mold-resistant products. Today, gypsum board manufacturers offer many enhanced versions of non-fire-rated and fire-rated Type X gypsum board panels with enhanced moisture and mold resistance.

Most common are paper-faced gypsum boards treated with bio inhibitors, products that prevent the growth of mold whenever moisture is introduced to the facing. Some manufacturers also now offer paperless gypsum board, with fiberglass mats in place of paper facings. The technology used to develop paperless gypsum board is similar to the technology used in manufacturing performance- proven moisture-resistant gypsum exterior sheathing products.

Both paper-faced and paperless treated gypsum boards with moisture-resistant cores have the highest mold resistance ratings of 10, as defined in ASTM D 3273, Standard Test Method for Resistance to Growth of Mold on the Surface of Interior Coatings in an Environmental Chamber, the industry standard for mold resistance. Paperless glass mat gypsum boards are higherpriced than treated paper-faced gypsum boards due to the difference in cost of the glass mat materials.

Since there is no limit to where mold spores can travel, it is wise to specify moisture- and mold-resistant gypsum board in all high-humidity climates and for any areas of a building that will likely have high moisture levels. These building areas include kitchens, showers, washrooms, locker rooms, basements, laboratories, laundry rooms and any area that will occasionally be exposed to splashes of water.

Seek Out Low-VOC Products
Most product manufactures have worked hard in recent years to reduce the VOC emissions of their products to very low levels. However, it is still important to check individual product data to be certain. Certification from the GREENGUARD Environmental Institute is one resource for determining if a product’s VOC levels are within acceptable limits.

Moisture Management in Ductwork
Well-insulated duct systems can help prevent mold growth by maintaining a constant temperature in the ductwork, significantly lowering the possibility of condensation on duct surfaces and protecting against microbial growth. According to the North American Insulation Manufacturers Association (NAIMA)1, fiberglass insulation is “inorganic and inert and does not support mold growth or act as nutrients for mold growth.” Fiberglass duct liners are also resistant to microbial attack, as described in ASTM C 13382 and as required by ASHRAE 62.13 for HVAC air stream surfaces. The duct liners are also in accordance to ASTM G 21-964 and ASTM G 22-965, as required by ASTM C 10716.

There are four types of fiberglass insulation commonly used in ductwork applications:
Fiberglass duct liner—insulation applied to the interior of a rectangular sheet metal duct and designed to control heat loss or gain through duct walls, assist with quiet air distribution and control condensation. Fiberglass duct liners are resistant to mold growth and fiber erosion in accordance with industry standards and prevent the distribution of airborne mold or glass fibers. There are two main types of fiberglass duct liner— textile, used in rectangular ducts, and rotary, used in cylindrical rotary ducts— as well as a rigid fiberglass duct liner that can be applied to the insides of metal ducts.

Fiberglass duct wrap—insulation that fits snugly over rectangular, spiral, flat oval or irregularly shaped duct surfaces. It is a resilient fiberglass blanket, factory- laminated to a vapor retarder facing, which can be easily cut and fitted to achieve a neat, thermally effective installation.

Fiberglass duct board—a 1- to 2-inch thick rigid board made from resin-bonded inorganic glass fibers and is used to build fiberglass ducts. For commercial applications requiring thermal insulation, condensation control and acoustic control, fiberglass duct board provides an efficient, lower-cost alternative to sheet metal. Today’s fiberglass duct board products are lighter in weight and more resistant to the erosion previously caused by mechanical cleaning. Because insulation is integrated with the duct board, it eliminates the extra fabrication steps required when applying thermal and/or acoustical insulation to sheet metal ducts. The outside surface of the boards feature a factoryapplied reinforced aluminum air barrier and a vapor retarder, protecting the fiberglass ducts from air leakage and moisture accumulation.

Fiberglass commercial board insulation— available unfaced, with FSK or ASJ facings—is applied on the exterior of round, rectangular, oval or irregularly shaped ducts, plenums, chillers and other HVAC equipment. Ranging from flexible to rigid, commercial board products are used to reduce heat loss or gain through duct, plenum or equipment walls.

In addition to insulating ductworks, facility managers should ensure that their facilities have HVAC mechanical equipment that efficiently ventilates spaces removing any stale air, unpleasant odors or chemical threats to IAQ, such as fumes from cleaning solutions.

Following the guidelines above will help to create a drier, mold-free interior environment, which in turn, will produce higher-quality interior air. High IAQ improves the health and wellbeing of building occupants. Students will likely be healthier, have fewer sick days and be more productive with cleaner air to breathe. For health care facility patients, high IAQ means fewer threats to their respiratory system, shorter recovery times and reduced risk of illnesses contracted during their stay. For the managers of the building, high IAQ and healthy occupants mean a safer facility with no threats of litigation for mold-related illnesses among occupants. Being proactive during the design process or taking steps to improve the IAQ of an existing facility are actions that truly benefit all parties
involved.

Stan Gatland is employed by the Certainteed Corporation.
1 Insulation Facts 34: The Facts About Mold Growth
2 Standard Test Method for Determining Fungi Resistance of Insulation Materials and Facings
3 Ventilation for Acceptable Indoor Air Quality
4 Standard Practice for Determining Resistance of Synthetic Polymeric Materials to Fungi
5 Determining Resistance of Plastics to Bacteria
6 Standard Specification for Fibrous Glass Duct Lining Insulation (Thermal and Sound-absorbing Material
 

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