Daylighting and performance considerations for polycarbonate glazing systems

Relationship between performance characteristics
A common misconception is viewing performance attributes as independent elements. Changes required in a product to achieve one particular performance number often will cause changes in other numbers.

For example, the percentage of opaque elements added to the resin composition of polycarbonate glazing to achieve a lower SHGC will decrease the amount of LT. Conversely, glazing with a higher LT percentage will have higher SHGC performance numbers.

Also, the thickness of a polycarbonate glazing system can be increased to provide a higher U-value, but this also can cause a corresponding decrease in LT.

Even flammability ratings have a cause-effect relationship in polycarbonate glazing systems, as various resin additives used for fire resistance will cause lower LT as well as changes in U-value, SHGC, and structural performance.

Working with the translucent exterior vertical wall manufacturer early in the design process is the best approach to select and specify a system meeting the project’s goals and requirements. Should any compromises be required to achieve better performance, aesthetic, or value, it is easier and less costly to accommodate these earlier in the design process and with the expertise of the manufacturer.

Jim Leslie manages all operational and strategic endeavors for Exterior Technologies Inc. (EXTECH). Supporting architectural designers and specifiers, he also oversees the company’s continuing education program and communications. A graduate of Penn State University, he has more than 15 years of experience in the architectural, engineering, and construction (AEC) industry. He can be contacted at

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