By Rick Scott, AIA

This is part 1 of 3.

The following case study presents an example of what Liberty Building Forensics Group encountered when excessive humidification, building positive pressurization, and a leaky building envelope combined to cause condensation, frost, and ice damage in a Midwestern medical facility.

Liberty was called in two years after construction to determine the most effective and least disruptive resolution to the now fully functioning facility’s problem. The designer had not properly specified an air barrier for the building, which led to the leaky envelope condition. These problems could have been avoided if the designer had specified proper materials, installation, and testing for the air barrier system.

Case Study

A 50-bed medical facility located in the Midwest experienced buildup of frost and ice in above-ceiling spaces, soffits, and in clerestories during winter months two years after construction was completed in 2006. The frost/ice (Figure 1a) would eventually melt (Figure 1b), wetting the ceiling surfaces, causing damage (Figures 2a and 2b), and leaking into the occupied rooms below. The facility owner and designer originally attributed the frost and ice buildup to an improperly installed air barrier system. While the presumptive “air barrier” was in fact not tight, an investigation also revealed the following:

  • The designer had specified exterior wall materials that were not capable of providing a tight air barrier.
  • The building heating, ventilating, and air-conditioning (HVAC) system contained humidifiers for patient comfort during the winter. These humidifiers were improperly operating and were set too high, causing excess humidity that led to the buildup of frost and ice in concealed cold spaces.
  • Building pressurization, as designed (based on interpretation of state regulations), played a role in pushing the humid interior air past the air barriers and into colder concealed spaces (exfiltration), where it condensed on cold surfaces and formed frost and ice.

Internet-connected wireless data loggers were used to show how properly operating the humidifiers without sacrificing occupant comfort solved the frost/ice problem.

Medical 1

Figure 1a: Frost forming on underside of metal roof deck in above-ceiling space.

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Figure 1b: Melting frost/ice dripping off underside of metal roof deck in above-ceiling space.

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Figure 2a: Warping and damage to wood bead board ceiling in porch areas attributed to water from melting frost/ice in above-ceiling space.

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Figure 2b: Damage to ceiling tiles due to melting frost/ice in above-ceiling space.

To be continued…

With over 35 years of experience, Richard S. Scott is an expert in the areas of architecture, interior design, and building forensics, with a focus on moisture-related building problems. He is certified by both the American Institute of Architects/AIA Florida and the National Council of Architectural Registration Boards (NCARB). He has published over 30 articles, and has lectured or presented at nearly 40 seminars or events. Mr. Scott has developed various training courses, including a 16-hour IAQ training course for NASA and an 8-hour water intrusion prevention training course for the Naval Facilities Engineering Command (NAVFAC). He can be reached at