INSULATION FACTS Facts About # Moisture and Fiber Glass 26 Metal Building Insulation Information from NAIMA

nlike many other insula- What effect does mois- tion products, fiber glass Q ture have on insulation metal building insulation performance? is often visible to the Uoccupants of the building. Making Moisture from rain, ground sure that roofs and walls do not A water,humidity or other leak, that the product is clean and forms of condensation creates the dry prior to installation, and that potential for several problems in condensation is controlled after metal buildings. First, the pres- installation is critical to the insula- ence of water (or ice) in the insu- tion performance and to the lation seriously degrades the building’s interior aesthetics. thermal performance and can Because of performance require- degrade the effective service life ments, fiber glass metal building of the insulation system. Second, insulations are most frequently water in contact with metals can installed with a facing material contribute to corrosion and laminated to the surfaces that may degrade the service life of the be visible.This facing serves building.Third, collection of several purposes: water can lead to dripping, stain- ing, and other undesirable effects Provides vapor retarder such as mold, mildew and odors, protection to retard passage of which degrade the building’s water vapor through the insu- intended service. lation to cold surfaces where condensation can occur Protects the insulation from damage Should wet insulation Provides light reflectivity Q be replaced? Provides an aesthetic appearance Yes. When fiber glass metal Fiber glass metal building insu- A building insulation is lation will provide long service exposed to storm waters or flood life and optimum performance damage, the wet insulation should when a few simple precautions be removed and replaced since are followed. The insulation the water may carry with it any should be kept clean and dry number of unknown contaminants. prior to installation and applied Although it is possible for the only to clean and dry surfaces. thermal and acoustical perfor- Care should be taken to protect mance of fiber glass insulation to the insulation from the incursion return if the material is allowed of water during the installation to completely dry out, there is no process. If adequately designed, assurance that the drying method regular inspection and mainte- used will be effective. There is www.naima.org nance of the vapor retarder will also no assurance that the forces protect the integrity of the acting on the wet insulation will system after installation. not result in loss of thickness, or for protection in the winter Materials rated at .02 perms are Facing Perm months when the inside ambient recommended where high Material Rating* air temperature is higher than the humidity interior conditions outside ambient air temperature. exist.Materials whose perm Vinyl 1.0 This is a design parameter ratings are greater than 1.0 are FSK .02 confirmed during installation. not considered to be vapor White Metalized retarders.General perm ratings The insulation must be Polypropylene Scrim Kraft .02 for the facings most commonly 2thick enough to maintain the used on metal building insulation Vinyl/Scrim/Foil .02 facing surface temperature above are shown in the table above. Polypropylene Scrim/Foil .02 the inside ambient air dew point Vinyl/Scrim/ temperature to prevent conden- Metalized Polyester .02 sation.This is a design parameter. References System thickness for condensa- 1. Fungal Contamination of HVAC * Perm ratings can be found in literature tion control may be different Surfaces: The Role of the Dew provided by the individual manufacturers of vapor retarder facings. from the thickness for energy Point in Microbial Amplification, conservation. Jerry J.Tulis, and Wayne R. Thomann; Occupational and that contaminants in the water Seams, joints, damage or punc- Environmental Medicine Division, will not contribute to corrosion, 3tures in the vapor retarder and Duke University Medical Center, mold or mildew growth or odors. penetrations should be sealed to Durham, N.C., 1997 For these reasons, it is best to err retard the passage of water vapor on the side of caution and replace around the insulation.This is 2. Ibid. the insulation. primarily an installation require- Fiber glass metal building insu- ment for good workmanship. lations must pass the mold Ventilation to the outdoors on About NAIMA growth test as specified in ASTM 4the cold side of the insulation NAIMA is the association for North C991: Specification for Flexible will help remove moisture that American manufacturers of fiber Glass Insulation in gets past the facing.This is a glass, rock wool, and slag wool insula- Pre-Engineered Buildings. Clean, design consideration. tion products. Its role is to promote dry fiber glass will not support energy efficiency and environmental 1 mold or fungus. However,once preservation through the use of fiber the insulation – or any product, glass, rock wool, and slag wool insula- for that matter – is exposed to How important is the perm rating of the tion, and to encourage the safe pro- dirt and moisture, the possibility Q duction and use of these materials. for microbial growth (mold or vapor retarder in con- 2 trolling condensation? mildew) exists. For additional information contact: Replacing the wet insulation is recommended to reduce the poten- The rate at which moisture NAIMA tial for indoor environmental quality A or water vapor passes 44 Canal Center Plaza, Suite 310 Alexandria, VA 22314 problems and to regain the energy- through a flat material induced by unit vapor pressure differ- Phone: 703-684-0084 efficiency and acoustical require- Fax: 703-684-0427 ments intended for the building. ence is defined as water vapor www.naima.org permeance. One perm is defined as 1.0 grain of water vapor trans- NAIMA BUILDING INSULATION mitted per hour per square foot What are some installa- COMMITTEE MEMBERS: per 1.0 inches of mercury vapor tion guidelines to protect CertainTeed Corp. Q pressure difference.The lower P.O. Box 860 against condensation? Valley Forge, PA 19482 the perm rating, the more effec- 800-233-8990 tive the retarder in controlling Controlling the condensa- moisture vapor transmission. Johns Manville tion in a metal building P.O. Box 5108 A When choosing a vapor retarder, Denver, CO 80217 depends on several design, instal- remember that the lower the 800-654-3103 lation and maintenance factors. perm rating means the less Knauf Insulation One Knauf Drive The insulation must have vapor water vapor that can pass Shelbyville, IN 46176 1retarder on the “warm-in- through the material. 800-825-4434 winter”side for the more severe Materials with a perm rating Owens Corning operating conditions. For most of 1.0 perms or less are consid- One Owens Corning Parkway buildings, this is the inside surface ered to be vapor retarders. Toledo, OH 43659 800-GET-P

Pub. No. MB 306 10/04