Solar Gain

What Is It?

Solar gain is the positive contribution to the heating of a building’s interior made by the sun’s energy passing through a glazed structure.      

Placement and Orientation

Where the glazed units are situated in the design of the building and the direction they face are significant factors affecting solar gain. Those facing south take advantage of solar gain in winter because the sun is low in the southern sky. North facing ones will have virtually no exposure to the direct winter sun and are usually net losers of energy. South and west facing exterior doors and skylights can cause overheating in summer as a result of unwanted solar gains from the hot afternoon sun.



A simple yet often overlooked factor that affects solar gain is the total glazed area. A glazed surface with a wide frame and numerous small panels divided by mullions and muntins has a much smaller total glazing area to capture solar energy than one of the same size, but with a narrower frame and single, undivided glazing area. The greater the proportion of glazing to frame area, the greater the amount of sun light that passes through, and the greater the potential for solar gain.


Glazing Choice

Single glazing will allow the most light and energy from the sun to pass through. Double glazed, compared to single glazed, reduces solar gain by about 10%. And triple glazed reduces it a further 10% for a total of 20% less than single glazed. However it is important to understand that the gains in thermal performance offered by double and triple glazed exterior doors and skylights over single glazed far outweigh the reduction in solar gain.

Solar Gain and U-Value

Technology such as low-E coating also can reduce solar gain for double glazed unit by 10% to 40%, depending on the coating.



Shading will affect solar gain as well. Roof overhangs and well placed deciduous trees planted in front of south and west facing exterior doors, patio doors and skylights will protect against overheating in summer but allow beneficial solar gain during the winter months.

Drapes, shades and blinds can control the amount of sunlight entering a building as well as the amount of heat loss that occurs when the sun is not shining. Keeping curtains open on sunny winter days allows maximum solar gain and then closing them at night, or on overcast days, reduces heat loss. Care must be taken to ensure proper installation that allows adequate air circulation between the curtain and the glazed surface to avoid condensation.