Energy is the first “E” in LEED, and one of the tenets of sustainability. The operational energy use and associated emissions to air during the life of the building is 85 to 95% of the total energy and emissions (including that embodied in construction materials and used for maintenance). Saving energy reduces the use of natural resources as fuel, the need for additional power plants to generate electricity, and the energy and emissions associated with obtaining and using these fuel sources.

Less to cool and heat. Buildings with exterior concrete walls, also called mass walls, utilize less energy to heat and cool than similarly insulated buildings with wood or steel frame walls.

Capacity to store energy. Concrete’s thermal mass has the capacity to store warmth or cold.

This results in moderate indoor temperature fluctuations, slower transfer of heat through the building envelope, and the ability of a building to store energy and shift peak energy requirements.

Energy savings due to thermal mass is dependent on climate. Mass has the greatest benefit in climates with large daily temperature fluctuations above and below the balance point of the building (55 to 65°F).

Comparison of Heating and Cooling Energy and Costs for Identical Houses
with Mass and Frame Walls in Boulder, Colorado (from PCA CD026).

Lowers peak loads. By lowering peak loads, energy dollars can be saved. For example, peak cooling loads in office buildings are often in mid-afternoon. Properly designed thermal mass can shift a portion of the load from mid-afternoon until later when the building is unoccupied or when peak load electricity costs are less.

Reduces size of HVAC system. Analytical and experimental studies show that the use of materials with thermal mass in buildings reduces heating and cooling peak loads, resulting in reduced HVAC system capacity requirements. Studies show that the HVAC system in a house with mass walls can be downsized from that of a house constructed with frame walls, even when the mass walls have less insulation.