Cool exterior walls, like cool roofs, are materials that strongly reflect sunlight (solar energy) and cool themselves by efficiently emitting any heat that was absorbed. The exterior wall surface stays cooler and reduces the amount of heat conducted into the building.
The exteriors of many buildings are painted, regardless of the underlying material used in construction (such as wood, cementitious fiberboard, or stucco), in which case the paint layer determines how well the wall surface will stay cool during the day. Other types of siding, like metal or vinyl, may be pre-painted or pigmented in the factory. Cool exterior walls are available in a variety of lighter and darker colors that use reflective “cool” pigments. These pigments are more reflective of infrared light without affecting the color of the product.
The amount of sunlight that hits the walls of a building differs from that of a roof over the course of the day and year, with less solar energy hitting the wall overall. However, walls also generally have less insulation than roofs, with about half the amount of resistance to heat flow than that of a roof. These two factors combined result in similar savings from cool exterior walls to that of cool roofs.
Cool exterior walls are evaluated using the same two properties as cool roofs – solar reflectance and thermal emittance. Both properties are measured on a scale from 0 to 1, where 1 is the most reflective or emissive.
The CRRC measures these two properties for exterior wall products, both for the product's initial values and after three years of outdoor exposure. The CRRC publishes the results in the Rated Wall Products Directory. The Directory enables you to compare the rated values of various product types and brands.
Visit Resources for Home and Building Owners to learn more about the benefits of cool exterior walls. Download our Fact Sheet with information for manufacturers, end users, and policymakers.
Effect of high-albedo materials on pedestrian heat stress in urban street canyons
Effectiveness of cool walls on cooling load and urban temperature in a tropical climate
Improving Thermal Performance of Single Family Homes in Hawaii through High Solar Reflectance Coatings on Above Grade Walls
Energy Savings by Using Reflective Paint on Exterior Walls at the UC Davis Campus
Investigating the Urban Air Quality Effects of Cool Walls and Cool Roofs in Southern California
Measured Cooling Energy Savings from Reflective Wall Finishes: Evaluation as an Efficiency Measure across Climates
Paints as a Scalable and Effective Radiative Cooling Technology for Buildings
Solar-Reflective "Cool" Walls: Benefits, Technologies, and Implementation
Supporting Information for Investigating the Urban Air Quality Effects of Cool Walls and Cool Roofs in Southern California
Supporting Information for Targeting buildings for energy-saving cool-wall retrofits: a case study at the University of California, Davis
Systematic Comparison of the Influence of Cool Wall versus Cool Roof Adoption on Urban Climate in the Los Angeles Basin
Targeting buildings for energy-saving cool-wall retrofits: a case study at the University of California, Davis
The effect of using a high-albedo material on the Universal Temperature Climate Index within a street canyon
Thermal Performance Analysis of Highly Reflective Coating on Residences in Hot and Arid Climates
The standard covers test specimen preparation and test methods for measuring the initial and aged radiative properties of roofing products. The standard is referenced by building codes and rating programs worldwide in order to measure the initial and aged solar reflectance and thermal emittance of roofing products.
California’s Building Energy Efficiency Standards for Residential and Nonresidential Buildings (Title 24, Part 6) contains requirements for the thermal emittance, three-year aged reflectance, and Solar Reflectance Index (SRI) of roofing materials used in new construction and re-roofing projects.
The L.A. Green Building Code requires roofing material used in residential buildings meet minimum values for three-year aged solar reflectance and thermal emittance, or aged SRI.