Thermal mass – masonry floors, walls and/or ceilings – absorb and store daytime solar heat in winter for release at night.
A large portion of the sunlight (heat gain) admitted into a space during the daytime must be stored inside the same space for release during the nighttime hours.
To store a portion of the heat gained, construct walls, floors and/or ceilings of masonry (concrete, brick, concrete block, adobe, etc.):
- A minimum 10 cm (4 inches) in thickness, with
- An exposed ‘surface area to solar glazing area ratio’ of 3:1 to 9:1.
The higher the ratio, the more heat stored and stable the indoor temperature becomes. Make ceilings and lightweight construction a light color, walls any color, and floors a medium to dark color. For exterior masonry walls, locate insulation on the exterior side of the wall so the masonry is exposed to the interior.
For more detailed information, see the In-Depth Information Page under Tools + Resources.