Tempered glass is a type of safety glass used for horizontal glass surfaces where additional strength is needed, like shelving or table tops. When used for these surfaces, tempered glass creates a clear view through the surface with better stability than traditional glass. Understanding the weight limits of that surface will prevent breakage from putting too great a load on the glass.

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The glass used for shelving needs to be tempered glass for additional support.

Tempered Glass

Tempered glass starts as regular glass, but after a heat treatment, the glass becomes stronger. Compared to regular glass, tempered glass is four times stronger, according to "Engineering Materials: Polymers Ceramics And Composites" by A.K. Bhargava. One of the characteristics of tempered glass is the way it breaks. Instead of creating shards, it falls apart into small pebbles of glass. This happens when a force is applied in a concentrated area on the glass after it has been tempered. To avoid the glass breaking, it must be ordered to size from the glass company. The company will cut and polish the glass before treating it with heat to strengthen it.

Distance Between Supports

The distance between the supports plays one role in how much weight the tempered glass can hold. The more space between supports, the less weight the tempered glass can handle. For instance, 1/4-inch thick tempered glass shelves should be supported no farther than 2 feet 4 inches apart to hold up small knickknacks. If you need wider spans, add support brackets in the middle of the length of the tempered glass.

Glass Thickness

Thickness is critical to the amount of weight the tempered glass can support. Thicker glass will hold up more weight than thinner glass. For surfaces that will need to support more weight than just a few picture frames, choose the thickest tempered glass you can find for the surface. The correlation between glass thickness to weight supported is not linear. For instance, a 1/4-inch thick piece of tempered glass supported every 1 foot will support about 292 lb per square foot. If you had a 3/4-inch thick piece of supported the same way, it could hold up about 3,268 lb per square foot.

Supported Weight

Combining the distance between supports and the thickness of the glass will help you to find the weight the glass will support. Weight for glass is given in pounds per square foot. You can use charts for traditional glass to estimate the load supported by tempered glass. Just multiply the numbers by four since tempered glass is four times stronger than traditional glass.