moldy wall pic

Understanding the patterns of moisture accumulation in buildings provides the basis for preventing moisture-related problems when commissioning a building or when analyzing the relationship between HVAC systems in the building envelope. Although mold and moisture growth staining and corrosion are the most visible signs of moisture-related damage and buildings, they are only symptoms of the fundamental problem of uncontrolled moisture flows. Thus, controlling the flow of moisture is key to preventing premature degradation of building components.

Moisture related building damage can result from any of the following events:

  • Intrusion of bulk moisture (i.e. rainwater and groundwater)
  • Moisture generated internally by human or operational activity
  • Moisture diffusion through building envelope materials
  • Leakage of moisture laden air into a building (i.e. outside air infiltration)
  • Moisture in ventilation airstream capillary flows

The architectural and mechanical engineering disciplines are responsible for controlling moisture in buildings. Architects are primarily responsible for controlling the infusion of rain and groundwater to the design of the water shedding qualities of the building envelope. While the mechanism of vapor diffusion is based on the engineering principles related to temperature and vapor pressure differences between conditions and unconditioned spaces specification and placement of the moisture vapor retarder for the exterior building envelope is normally the architects responsibility.

Mechanical engineers are responsible for controlling internally generated moisture and moisture in the ventilation airstream through designing, sizing, and specifying air conditioning equipment. Airflows induced by the mechanical systems must be controlled so that the potential for airflow across the building envelope is from the cool, dry environment toward the warm, hot environment. Unfortunately, the level of coordination required between the architectural and engineering disciplines to prevent moisture control problems rarely exists.

This post was taken from an article titled, “Moisture Problems: Why HVAC Commissioning Procedures Don’t Work in Humid Climates”. by George DuBose and J. David Odom, and Philip Fairey, and was previously published by CH2M Hill.