What does the term 'thermal mass' refer to in building design?

The term 'thermal mass' in building design refers specifically to the capacity of building materials to absorb, store, and later release heat energy. Materials with high thermal mass, such as concrete or brick, can stabilize indoor temperatures by absorbing heat during the day when temperatures rise and then releasing that heat at night when temperatures drop. This property leads to enhanced energy efficiency, as it helps reduce the need for heating and cooling by mitigating temperature fluctuations within the building.

Other choices, while related to building design, do not accurately define thermal mass. The weight of roofing materials, the volume of insulation, and the construction materials used encompass different aspects of building performance and construction, but they do not capture the essence of thermal mass, which is fundamentally about heat energy storage and release.