What is glazing heat gain and how does insulation interact with windows?

• A. Glazing heat gain is heat entering through windows; insulation improves wall and roof, while windows require low U-value and shading; insulation does not compensate for poor glazing.
• B. Glazing heat gain is heat entering through walls.
• C. Glazing heat gain is not influenced by insulation.
• D. Insulation can fully compensate for poor glazing.

Answer: (A)

Glazing heat gain is the heat that enters a space through the window assembly, from both heat conducted through the glass and frame and heat gained from solar radiation passing through the glazing. Insulation’s role is to slow heat flow through opaque parts of the building, like walls and the roof, not to control how windows perform. Windows need a low U-value to minimize heat transfer and shading or other solar-control measures to limit solar heat gain. Even with good insulation on walls and roofs, poor glazing will allow significant heat to enter, and insulation cannot fully compensate for that shortcoming. So the best approach is to reduce glazing heat gain with appropriate glazing properties and shading, while using insulation to cut heat flow through the rest of the envelope.