If the goal is to limit solar heat gain through windows, which property should be prioritized?

• A. Lower solar heat gain coefficient
• B. Higher U-value
• C. Larger fenestration area
• D. Higher emissivity of glass

Answer: (A)

To limit solar heat gain through windows, prioritize reducing the amount of solar energy that passes through the glazing. This is captured by the Solar Heat Gain Coefficient (SHGC): a lower SHGC means less solar radiation enters and becomes heat inside the building, helping keep interiors cooler and reducing cooling loads. You achieve this with glazing options and coatings designed to block or reflect solar energy, such as low-emissivity (low-E) coatings, tinted or spectrally selective glass, and appropriate glazing layers.

Choosing a higher U-value won’t directly limit solar gain; it indicates how well the window insulates against conductive heat transfer due to temperature differences, not the sun’s heat. A larger fenestration area increases total solar heat gain simply because more glass is exposed to the sun. Higher emissivity of glass can alter radiant heat transfer but doesn’t specifically reduce the solar energy that enters as heat, so it’s not the best lever for limiting solar gain.