A material\u2019s thermal mass denotes its ability to store heat within a cycle of time. K-values, generally calculated on a 24-hour cycle, are important because they give general references to a material\u2019s capabilities for storing heat. All materials may be considered for use in a thermal mass calculation, but steel, aluminum, and other metal claddings tend to cycle too quickly, while wood tends to cycle too slowly to offer desirable design values.<\/p>\n
Masonry\u2014such as concrete masonry unit (CMU), stone, and brick\u2014offers a good blend of characteristics for the thermal mass design based on several values. Storing heat well, the dense material can be designed with wall thicknesses that allow for normal window and door jamb details with reasonable per-area costs to construct.<\/p>\n
In most cases, thermal mass should be measured on a cycle representative of both a typical heating and cooling cycle or a variable daily winter cold temperature cycle. While this is done for either season with the same principals, external factors contribute to the winter wall calculations in a more direct way. Building orientation, ceiling heights, lighting, solar heating, soffits, wall finishes, number of occupants, and usage round out a general list for design.<\/p>\n
In colder climates, thermal mass is based on the function of interior heating cycling through the core of the wall. As the evening temperatures fall and the interior begins to feel cooler, warmth that was gained and stored during the daylight hours can then reverse the heat path and move back to the interior space of the building.<\/p>\n