Heat Gains, Heat Losses, and Thermal Insulation

Heat flows naturally from a warmer space to a colder space. Heat that flows into the building is called heat gain, while heat that flows out of the building is called heat loss. When too much heat gain (loss) occurs, your air conditioning system (heating system) operates to keep the space comfortable. A large amount of heat can be gained (or lost) through a building’s roof. Cool roofs reduce heat gains throughout the year. This can save you energy on cooling, but it can also increase the energy you need for heating. Often, the annual cooling energy cost savings is substantially higher than the heating penalty.

Thermal insulation can greatly reduce the amount of heat lost or gained through a roof system. Even though cool roofs reduce solar heat gains, they are never a substitute for using sufficient thermal insulation. Insulation reduces heat losses and heat gains through the roof in ways a reflective surface cannot.