Employing moisture-management tactics in commercial-building wall-assembly design to increase thermal efficiency and minimize the potential for indoor-air-quality- (IAQ-) threatening mold growth has become popular in recent years. Another important tactic for mold prevention is ductwork insulation. This article will discuss the role fiberglass duct insulation can play in mold prevention.

HVAC SYSTEMS: THE LUNGS OF A BUILDING

Mold and microbial growth often occurs inside uninsulated sheet-metal ductwork in which excess moisture is present. Caused by changing temperatures, this moisture often arises from condensation on the inside and outside of HVAC ductwork. During summer, beads of moisture form on the interior or exterior of warm, uninsulated ducts as cold air travels through. During winter, the same situation occurs as heated air travels through cold ducts. Condensation will occur on any duct surface when its temperature is equal to or lower than the dew-point temperature. IAQ concerns begin when condensed moisture mixes with dust or dirt in uninsulated ducts, fostering mold and microbial growth. If condensation is left untreated, mold and microbial growth will continue to worsen, leading to contaminated interior air.

Airborne mold spores can lead to discomfort and a variety of health problems among building occupants, including headaches, irritability, and severe respiratory ailments, such as asthma and Legionnaires' disease. ANSI/ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, provides guidelines for improving IAQ by combating these problems. Among other solutions, Standard 62.1 recommends adding fiberglass insulation to HVAC ductwork.

Well-insulated duct systems can help prevent mold growth by maintaining a constant ductwork temperature, significantly lowering the possibility of condensation on duct surfaces and protecting against microbial growth. According to the North American Insulation Manufacturers Association (NAIMA), fiberglass insulation is “inorganic and inert and does not support mold growth or act as nutrients for mold growth.”¹ Fiberglass duct liners also are resistant to microbial attack, as described in ASTM C1338, Standard Test Method for Determining Fungi Resistance of Insulation Materials and Facings, and required by Standard 62.1 for HVAC air-stream surfaces. The duct liners also are in accordance with ASTM G21-96, Standard Practice for Determining Resistance of Synthetic Polymeric Materials to Fungi, and ASTM G22-76, Standard Practice for Determining Resistance of Plastics to Bacteria, as required by ASTM C 1071, Standard Specification for Fibrous Glass Duct Lining Insulation (Thermal and Sound Absorbing Material).