Extreme heat causes more deaths in the United States than any other natural disaster.

Discussions around the role of buildings in heat mitigation and resilience often focus on air-conditioning, and while A/C can be lifesaving, it also increases peak cooling demand, greenhouse gas emissions, and waste heat released back into the environment. Further, regions with historically cooler climates and low percentages of air-conditioned homes are now experiencing longer, more frequent, and more intense heat waves, leaving residents without A/C at risk of heat illness and death.

Incorporating passive cooling strategies in new construction and building retrofits is critically important to improve heat resilience in buildings without access to A/C and to reduce A/C demand in conditioned spaces.

Like cool roofs, which are required for most buildings in California and for commercial buildings in several other U.S. cities and states, cool exterior walls efficiently reflect solar radiation back into the atmosphere instead of transferring it as heat into buildings. For a single building, this helps reduce solar heat gain, indoor temperatures, and A/C use, while increasing resilience to extreme heat, particularly in buildings with little insulation or that do not have or are unable to operate A/C. On a larger scale, this helps raise the community’s albedo, lower outdoor temperatures, mitigate heat impacts, reduce peak cooling demand, and decrease greenhouse gas emissions.

This presentation will describe the impacts of cool exterior walls on buildings and communities and the radiative properties of solar reflectance and thermal emittance, which determine the coolness of a wall surface. It also will provide examples of potential HVAC energy cost savings resulting from cool exterior wall use in different U.S. climates and equip attendees with the ability to estimate building-specific savings using a publicly available tool developed by Lawrence Berkeley National Laboratory. Additionally, the presentation will summarize wall radiative property provisions in codes, standards, and programs, including the 2024 International Energy Conservation Code, ASHRAE Standard 90.1, and LEED v4.1, and provide a tutorial for how to find and interpret independently verified radiative property data for exterior wall materials.