Presenter Information

Ronald B. Shankland Jr.


The harm incurred by structures, equipment, and people due to window unit failure during a windstorm is drastically reduced if the glass remains in the frame until the storm has subsided.

There are basically two types of window glass used in curtain wall cladding systems: heat treated and annealed. Heat treated glass is tempered during its manufacture so that it retains residual surface stresses in the range of 3500 psi to 10,000 psi, or more. Annealed glass is cooled very slowly under controlled conditions in order to remove undesired internal stresses (Reznik, 1987). Also known as float glass, annealed glass is manufactured by floating molten glass on a bed of molten tin and then allowing it to cool very slowly (Minor, 1990a). Annealed glass is generally less expensive and easier to cut to size than heat treated glass. It is the basic type of glass used in architectural glazing (Minor, 1990a).

These two basic types of glass can be used as a single layer (monolithic) or combined (laminated or layered). Previous research (Behr et al., 1985; Reznik et al., 1987; Vallabhan et al., 1987; and Pantelides et al., 1991) has shown that laminated glass performs well in windstorm situations, especially if the glass is held in the frame with a silicone sealant.

In order to improve resistance against fallout after breakage, it has been proposed that a surface film (usually polyester) be applied to monolithic annealed glass. An economical way to make new window glass safer, it may also be a relatively inexpensive way to retrofit existing windows.

Document Type


Presentation Date

April 1991