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The Straight and Narrow Preventing Wall Deflection
b y D o n n H a r t e r

The term “air-gap” refers to interior glazed partition walls where the vertical unsupported edges are similar to a butt joint, but without a silicone bond between the vertical edges. The International Building Code (IBC) states:

2303.4 Interior Glazed Areas. Where interior glazing is installed adjacent to a walking surface, the differential deflection of two adjacent unsupported edges shall not be greater than the thickness of the panels when a force of 50 pounds per lineal foot (psf) (730 N/m) is applied horizontally to one panel at any point up to 42 inches (1,067 mm) above the walking surface.

This design of glazing is popular in department stores and other retail locations where there is an uninterrupted view to merchandise on the opposite side. These vertical tempered panels often extend from the floor to a height of 12 inches above the walking surface, with the only support being at the top and bottom. This type of glazing will deflect when a person leans against it for support. An example might be an adult who leans against the glass for support to tie a shoe. If an accompanying child were to slide his/her hand into the deflected panel and the gap is greater than the thickness of the glass, serious injury could result when the pressure is released.

CODE TALK
The code eliminates the impending hazard by limiting the deflection to the thickness of the glass.

I find that too many installations specify 3⁄8-inch glass where ½-inch glass would be the only safe and complying minimum. Other than increasing the thickness of the glass to eliminate the scissors-like deflection between two unsupported vertical edges, the best option would be to silicone the joint, install clips or install a glass stiffener (an expensive option).

 

USG
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