Concrete masonry's thermal performance depends on its steady-state thermal characteristics (described by R-value or U-factor) as well as the thermal mass (heat capacity) characteristics of the assembly.
The steady state and mass performance are influenced by the size and type of masonry unit, type and location of insulation; finish materials, density of masonry, climate, and building orientation and exposure conditions.
Thermal mass describes the ability of materials to store heat. Because of its comparatively high density and specific heat, masonry provides very effective thermal storage. Masonry walls remain warm or cool long after the heat or air-conditioning has shut off.
This, in turn, effectively reduces heating and cooling loads, moderates indoor temperature swings, and shifts heating and cooling loads to off-peak hours. Due to the significant benefits of concrete masonry's inherent thermal mass, concrete masonry buildings can provide similar energy performance to more heavily insulated frame buildings.
The benefits of thermal mass have been incorporated into energy code requirements as well as sophisticated computer models. Energy codes and standards such as the International Energy Conservation Code (IECC) (ref. 1) and Energy Efficient Standard for Buildings Except Low-Rise Residential Buildings, ASHRAE/IESNA Standard 90.1 permit concrete masonry assemblies to have less insulation than frame systems to meet the energy requirements, due to their thermal mass.