Condensation at Curtain Wall and Storefront Spandrel Infill

Glazing Systems

Curtain wall and storefront glazing systems are typically a thin, non-structural outer façade element of a building that can span multiple floors or be incorporated into a punched opening. Glazing systems function largely as air and water vapor barriers, resisting air or water infiltration and accommodate building and system movement induced by wind, thermal, and seismic forces. Glazing systems support their dead load weight forces and provide no structural support to the building. As such, lightweight materials can be used in their development. Commercial glazing systems are typically constructed of aluminum-framed walls with glass, metal panels, louvers, operable windows or vents, or stone veneer infills. Building envelope consultants will often advise designers on curtain wall and storefront requirements for building movement, thermal expansion and contraction, water diversion, and thermal efficiency.

Spandrel Infill

Spandrel infill can enhance the visual impact of glazing systems and are used in place of vision glass where there is a need to hide the edges of floor slabs, insulation, ceiling details, and other building elements that would otherwise be seen through vision glass. Opaque glazing, metal panels, MCM (metal composite materials) panels, or insulated laminated panels are typically utilized as spandrel infill. When insulation is utilized inboard of the spandrel infill, an air space is routinely introduced to prevent thermal damage to the spandrel infill. Unfortunately, the air space can provide an opportunity for condensation to form on the interior face of the spandrel infill.

Condensation Formation at Spandrel Infill

Weather conditions, exterior temperatures, and glazing system design can have a tremendous impact on the likelihood and the rate of condensation formation at spandrel locations.

Condensation formation on spandrel infill is most likely to occur during extreme winter conditions when insufficient heat is supplied from the interior to prevent interior infill surface temperatures from remaining above the dew point. When interior surface temperatures dip below the dew point, water molecules start to form on the interior surface of the spandrel infill. Conditions that can contribute to condensation are the glazing system geometry, large amounts of interior insulation, uncontrolled air migration into the spandrel air gap, and long distances from heat sources. Should poorly designed spandrel conditions be left unattended, condensation can result in moisture or aesthetic damage to the spandrel panel and/or interior surfaces.

Condensation Damage at Spandrel Infill

When condensation forms at the spandrel infill of a glazing system, multiple types of damage can occur, and the effects of condensation can be far-reaching. In addition to moisture damage and microbial growth, condensation development on spandrel infill can also have a negative effect.

• Moisture Damage: Even if the glazing system is resistant to water infiltration from outside, condensation and moisture can still develop on the spandrel infill. This moisture can be absorbed by the surrounding components, causing damage to the assembly and adjacent surfaces.
• Microbial Growth: As condensation develops in these unventilated areas, microbial growth may develop and spread to adjacent areas, causing more damage.
• Aesthetics: Condensation buildup in these areas can damage glazing spandrel coatings.

In addition, combinations of these types of damage can occur, causing progressive damage that will require professional remediation.

Dealing with Existing Condensation at Spandrel Infill

Qualified professionals can recommend proven methods to mitigate conditions and remediate any existing damage caused by glazing system spandrel infill condensation.

• HVAC Systems: One way to delay the formation of condensation on the glazing system spandrel infill is to utilize the building HVAC system. By increasing airflow near these locations, more heat will be transferred to the assembly and increase interior surface temperatures. Another way to utilize the HVAC system is by reducing the interior relative humidity set points with respect to outside temperature. By reducing the amount of available moisture, condensation formation and possible accumulation can be delayed.
• Sealing Horizontal-to-Vertical Locations at Spandrel Infill: Another method of deterring condensation is by sealing the horizontal-to-vertical mullion joints at the spandrel cavity to prevent uncontrolled air migration into the cavity. Typically, an uncontrolled interior is moisture laden and when it comes into contact with the spandrel infill, which is below the dew point, it increases the amount of condensation formation.

Minimizing Condensation Through Initial Design

The most effective means to minimize condensation is during the initial system design. In addition to incorporating rehabilitation methodology, ways to minimize condensation potential during design include:

• Curtain Wall vs. Storefront: Typically curtain wall systems have higher resistance to condensation than storefront systems. Utilizing curtain wall is one way to minimize, or delay the onset of condensation formation.
• Thermal Modeling: At Lerch Bates, we offer 2-D thermal modeling (THERM®) to assist our clients with the design of spandrel areas. THERM® is a tool that uses two-dimensional conduction heat-transfer analysis methodology based on the finite-element method to determine material surface temperatures. By knowing surface temperatures, Lerch Bates is able to determine under which conditions condensation will occur, as well as identify transition points at which condensation will not develop, making it easier to predict and remediate. In addition, various configurations can be modeled to maximize interior surface temperatures.

• Install Vented Back Pans into the Glass Pocket: Installing back pans into the spandrel infill glazing pocket, which are vented to the exterior with insulation outboard of the pan, promotes increased interior surface temperatures with the added benefit of minimizing heat transfer through the spandrel infill. If condensation should occur within the insulation, it is outboard of the back pan and able to migrate to the exterior through the glazing weep system.
• Design Without Insulation: It is possible to maximize interior surface temperatures by eliminating the use of insulation at the spandrel infill location. Keep in mind if you design without insulation at spandrel infill locations, there will be a greater energy loss through the assembly and therefore larger HVAC heat loads.

How Lerch Bates Can Help

At Lerch Bates, we can help you each step of the way, whether you recently discovered condensation and are looking for remediation and management solutions, or whether you are designing a building and aim to minimize the potential for condensation at spandrel infill locations. Contact us today for more information.

–Ryan Krug