Frozen frames: The costly window mistake

by jason_cramp | May 11, 2024 1:02 pm

[1]

Completed in the mid-90s, a multi-story healthcare facility in the northeastern U.S. reported recurring condensation and frost on exposed interior frame and glass surfaces of its existing window assemblies during cold winter periods.

In addition, water damage to the interior gypsum wallboard finish at soffits above the window assemblies occurred repeatedly with early Spring’s notable warming trends. The facility’s vertical enclosure primarily consisted of thermally improved, aluminum-framed storefront systems in punched openings within 127-mm (5-in.) thick architectural precast concrete (APC) panels. Its opaque vertical enclosure’s thermal control layer included foil-faced batt insulation against the APC panels’ interior face.

Further investigation revealed multiple conditions contributing to condensation and/or ice on interior surfaces of the building’s exterior vertical enclosure components, including:

• The window head and jamb framing members were found to be in direct contact with APC panels, thus short-circuiting the integral thermal break in the storefront assembly. In addition, the continuous extruded aluminum subsill beneath the storefront’s sill member lacked a thermal break and was also in direct contact with the APC panels. This thermal bridging around the storefront assemblies increased the potential for condensation risk along the window assemblies’ perimeter.
• Widespread discontinuities in the batt insulation’s foil facer, including untaped seams, punctures, tears, and inadequate termination at floor slabs and window frames, were observed. Further, lack of access prevented installation of foil-faced insulation at spandrel beams below the structural deck above. As the foil-faced insulation serves as an interior air barrier, vapor retarder, and thermal control layer for the APC panel system, its breaches and discontinuities allowed moisture-laden interior air to migrate through and contact the APC panels’ interior surface, leading to condensation and ice formation when the surface temperature dropped below dew point. It was determined the recurring water damage at soffits reported in the early Spring resulted from winter-accumulated ice melting on the APC’s interior surface.
• The ambient interior environment was found to remain consistent year-round, maintaining a constant interior dry bulb temperature of approximately 21.1 C (70 F) and relative humidity (RH) above 45 percent. This led to a corresponding dew point above 8.3 C (47 F), which also increased the potential for condensation during colder winter months.
• Although linear supply air diffusers were positioned above the windows, they did not cover the window assembly’s full width. Further, with diffusers supplied by variable volume terminal units, the air wash across the plane of the windows was inconsistent, lessening the effectiveness of a uniform air wash across the entire window assembly.

In addition to water damage to interior finishes from repeated condensation/frost on APC panels and window assemblies’ interior surfaces, the accumulation of moisture over time within the interstitial exterior wall cavity (which was hidden from view) resulted in the formation of suspect organic growth on the back of gypsum wall board finishes, batt insulation, and APC panels’ interior surfaces.

Addressing post-construction conditions contributing to condensation in a mission-critical facility can be costly and disruptive. Therefore, it is paramount for the project team to properly understand the function and interrelationships of the exterior enclosure’s components to better ensure the effective control and management of moisture loads anticipated during in-service conditions. This includes proper detailing of the various control layers at interface conditions between adjacent enclosure assemblies to mitigate problematic and/or incomplete conditions in the enclosure that could affect in-service performance.

[2]Jeffrey Sutterlin, PE, is an architectural engineer and associate principal with Wiss, Janney, Elstner Associates[3] (WJE) in Princeton, New Jersey, office. He specializes in investigation and repair of the building enclosure. He can be reached at jsutterlin@wje.com[4].

[5]David S. Patterson, AIA, is an architect and senior principal with Wiss, Janney, Elstner Associates[3] (WJE) in Princeton, New Jersey. He specializes in investigation and repair of the building enclosure. He can be reached at dpatterson@wje.com[6].

The opinions expressed in Failures are based on the authors’ experiences and do not necessarily reflect that of The Construction Specifier or CSI.

Source URL: https://www.constructionspecifier.com/hospital-window-condensation-thermal-bridging/

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