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Solar gains are the measure of the amount of warmth from the sun which enters the property via your windows. The type of glass installed can vary enormously from the old single pane glass to modern hi-tech sealed glazing systems. The glazing type, qualtity, and the direction in which it faces, are all included in the calculation. The glass not only has an effect on whether heat can leave the property, and how fast, but also increases the warmth entering the property, and thus has a large effect on the overall SAP calculations.

The calculations also determine whether the property is likely to overheat, and in this likelihood, the SAP analyst can suggest measures which can be taken to avoid this potentially dangerous situation, such as adequate ventilation, alternative glass type, and screening, such as blinds.

Solar heat gain coefficient

The solar heat gain coefficient expresses the ratio of the sum of directly transmitted solar radiation and the amount of absorbed radiation entering the space through a window to the external solar radiation.

Shading coefficient

is the dimensionless ratio of the total solar heat gain from a particular glazing system to that for one sheet of clear 3-mm double-strength glass.

Overall solar transmission

is the total direct transmission of solar radiation through a window system including direct and diffuse radiation.