A Burning Question Revisited

In recent decades the use of unitized glazing systems has become increasingly common especially for high-rise construction. The opaque panels in unitized glazing systems have traditionally been insulated with mineral wool insulation installed within the aluminum frame behind a glazed spandrel. The interior face of the mineral wool is typically flush with the interior frame and finished with a foil facer or a galvanized sheet metal back pan.

Increasing code requirements for energy efficiency of opaque wall assemblies has led to the common practice of providing an additional layer of insulation inboard of the unitized glazing system. In colder climates, however, the practice of insulating inboard of the unitized glazing systems raises the concern of condensation on the surfaces of the glazing system now shielded from exposure to the interior heat source. This risk is further increased if the assembly inboard of the unitized glazing system is not airtight and the interior insulation is not in continuous intimate contact with the interior face of the unitized glazing system. The increased risk of condensation is especially elevated in residential buildings with their higher levels of interior humidity, limited ventilation and increasingly a lack of perimeter heating. The application of spray foam on the inboard face of glazing systems has been used in recent years as one means of mitigating the risk of condensation.

The use of foam insulation as part of building enclosures has received increased scrutiny in recent years and numerous envelope assemblies have been successfully tested to CAN/ULC S134 or its US counterpart NFPA 285. However, most of these assembly specific tests have been performed on stud wall assemblies. The following builds on a previous paper describing the testing of metal panel spandrel with interior spray foam insulation and outlines the results of testing spray foam insulation inboard of the glazed spandrel a unitized glazing system. It demonstrates how these assemblies can also meet the requirements of these standards.