R-Values Are Just Part of the Story

R-values provide a measure of resistance to heat flow in walls or other building elements. They are useful in gaining initial understanding of heat flow in buildings, and for calculating peak heating loads. They are unable to account for heat capacity. Therefore, R-values are of limited usefulness in understanding long-term cooling or heating loads, or for predicting annual energy costs.

Excerpt From California Second Generation Nonresidential Energy Standards

This energy standards excerpt shows that less wall Insulation, or total R-value, is required as the heat capacity of the wall increases. Annual energy performance remains equivalent. (Heat capacity Is the technical term for thermal

Energy Standards Recognize Masonry's Benefits

Energy standards are beginning to recognize the benefits of masonry's thermal mass. California's recent energy standards, developed through extensive computer analysis and research, provide a direct credit for thermal mass. Because the benefits are related to changes in daytime temperature and solar heat gain, this credit varies from climate to climate.

These two wall assemblies are equivalent in performance. One is a stud wall containing insulation with an R-value of R-11. The other is a solid grouted masonry wall with no insulation. Put into otherwise identical buildings in a hot climate, they result in equivalent annual energy performance.

Modifying Masonry's Thermal Performance

Masonry walls with solid grouted cores provide maximum thermal mass. Masonry walls can also be insulated, to obtain different thermal performance characteristics or to meet other energy code requirements.

Interior Masonry Walls Save Energy, Too

Interior masonry walls work much like their exterior counterparts, but excess heat is absorbed from inside rather than outside. During the day, the walls absorb heat from inside the building - accumulated heat from the sun, lights, equipment and people. At night the heat is released. This helps cool the building during the day and keep it warm at night. Passive solar heating systems rely on interior thermal mass.

In the summer months, interior masonry can be "precooled" by nighttime ventilation of the building to better absorb heat and cool the building during the day.