Curtainwall and window wall systems today commonly use insulating glass units (IGUs) for vision glazing and for spandrel panel cladding. A risk for IGU in insulated spandrels is higher thermal stresses on the glass lites, compared to older approaches with single glazing. When ceramic enamel (frit) opacifiers are used, there is increased stress from solar absorption. Thermal stress is generally addressed by heat-treating at least the opacified lite. Multiple incidences of thermal stress-related fracture of ceramic enameled spandrel glass in North America, Europe, and elsewhere have shown that ceramic enamel weakens glass, reducing the added benefit of heat treatment, so there remains a risk of in-service thermal stress breakage.

This presentation will give examples of breakage, describe causes, show results of a test program that shows ceramic enamel reduces the strength of heat-treated glass, and describe options to control the potential for in-service breakage. The discussion will be of interest to building owners, designers, and builders considering the use of curtainwall and window wall systems with opacified glass.