What is Unitized Structural Glazing?

A “unitized” curtain wall system is one in which the framing members are pre-assembled in factory, into units which are typically 4 ft wide and one story tall. Then, the vision glass and spandrel materials are installed into the units in the factory. All glazing gaskets and joinery sealants are factory installed; however, perimeter sealants would still be field installed. These assembled and pre-glazed units are then shipped to the jobsite for field erection. Vertical and horizontal mating joints can either be dry sealed with gaskets or wet-sealed with field-applied sealants. Making joints can be a male/female configuration.
Unitized systems handle these movements better when the glass is silicone glazed, and either system, when properly designed, can usually be made to work well for conventionally glazed applications. Wind loading is transmitted form the glass or infill material to the horizontal and vertical mullions. In semi-unitized systems, the vertical mullions can span two floors (twin-span) and provide greater structural efficiency than single-span mullions typically used in unitized systems. However, if the mullion expansion joint is near stool height (approximately 700mm above “zero moment” or continuous-span design, which is even more efficient than twin-span design, and can be utilized with either a semi unitized or unitized approach.