Insulating glass is primarily rated by which measurement?

The correct choice for the primary measurement used to rate insulating glass is the U-value. The U-value reflects the overall heat transfer coefficient of the insulating glass unit, measuring how much heat escapes through the glass. A lower U-value signifies better insulating properties, meaning the glass is more effective at preventing heat loss. This value is critical in evaluating the thermal performance of windows and glass facades in buildings, especially in energy efficiency assessments.

Understanding the importance of U-value helps in compliance with building codes and energy performance standards, making it essential for glazing contractors to consider during their work. While other measurements such as R-value, SHGC, and LR are relevant in certain contexts, the U-value is specifically designed to address the insulating performance of glass, making it the primary metric for evaluating insulating glass.