Thermal mass on the interior of the building is able to store heat or cold, and then slowly release it back out to the surrounding air. Heat from a sunny winter day as well as the coolness of a summer night can be retained inside the insulated shell of the exterior walls if the building incorporates adequate thermal mass. Thermal mass is needed to prevent daytime overheating of the structure and to stabilize its ambient temperatures through nights and periods of cloudy weather.  The more mass is available, the more stable the interior temperature.  Also, the more directly the winter sun hits the mass, the higher the solar heat gain.

Floors can provide a good source of mass. Concrete, brick, flagstone, or other masonry materials work especially well.  Any of these can be layered over with cork — an organic material that insulates well, and has the advantage of creating a softer surface underfoot.  Earth floors can be used, but do not perform as well.  Insulating beneath the floor helps to return the heat gains to the interior of the building more quickly.  Interior walls and houses are often framed with wood, but if built out of masonry materials such as rock or adobe, these can provide excellent mass, especially those interior walls hit directly by the sun. Concrete poured between studs is a quick way to add mass. (more…)