A cool roof is a roof designed to reflect more sunlight and release absorbed heat more efficiently than a standard roof. In California, cool roofs aren’t just an option. They’re required by state building code for most new construction and many reroofing projects, depending on your climate zone and roof type. The goal is straightforward: keep buildings cooler, cut air conditioning costs, and reduce the dangerous heat that builds up in California’s cities.
How a Cool Roof Works
Two properties make a roof “cool.” The first is solar reflectance: how much incoming sunlight the roof bounces back instead of absorbing. The second is thermal emittance: how efficiently the roof radiates away whatever heat it does absorb. A conventional dark asphalt roof might reflect only 5 to 15 percent of sunlight, absorbing the rest and heating up dramatically. A cool roof reflects a much larger share and sheds the remainder faster.
These two properties work independently. Solar reflectance deals with the visible and near-infrared light from the sun (short wavelengths), while thermal emittance deals with the infrared heat the roof radiates back out (long wavelengths). A roof needs to perform well on both measures to qualify as cool.
California’s Title 24 Requirements
California’s building energy code, Title 24 Part 6, sets minimum reflectance and emittance values that roofing products must meet. The specific thresholds depend on three things: whether your roof is steep-slope (pitched, like most houses) or low-slope (flat or nearly flat), which of California’s 16 climate zones you’re in, and whether the project is new construction or a reroof.
For single-family homes, steep-slope cool roofs are required in climate zones 10 through 15 for new construction and zones 4 and 8 through 15 for reroofing. These are the hotter inland and southern areas of the state. The minimums are relatively easy to meet: an aged solar reflectance of 0.20, a thermal emittance of 0.75, or a combined solar reflectance index (SRI) of at least 16.
Low-slope roofs face stricter standards. For new single-family homes in zones 13 and 15, and for reroofing in zones 4 and 6 through 15, the aged solar reflectance jumps to 0.63, with the same 0.75 thermal emittance requirement and an SRI of at least 75. Nonresidential buildings and multifamily buildings have their own parallel requirements, but the general pattern is the same: all new or replacement low-slope roofs across the state must be cool roofs.
The “aged” part matters. Roofing products get dirty and weather over time, so California measures reflectance after three years of exposure rather than when the product is brand new. If you’re replacing more than 50 percent of your roof or more than 2,000 square feet (whichever is less), you’ll need to meet these standards. An updated energy code takes effect for permits filed on or after January 1, 2026.
Materials That Qualify
Cool roofs come in a wider range of materials than most people expect. You don’t have to paint your roof white, though white coatings on flat commercial roofs remain one of the most effective options.
For homes with pitched roofs, the choices include:
- Asphalt shingles surfaced with light-colored or specially engineered “cool-colored” granules that reflect infrared light even in darker shades
- Clay and concrete tiles, including traditional terra cotta, which is naturally cool; tiles with reflective glazes; or tiles with reflective polymer coatings
- Metal roofing coated with reflective paint or surfaced with reflective granules
- Polymer or composite shingles with cool-colored pigments
- Wood shingles or shakes, which are naturally cool but less common due to fire concerns in much of California
The key innovation in recent years is cool-colored pigments. These specially formulated coatings reflect the invisible near-infrared portion of sunlight (which carries about half its heat energy) while still looking dark to the eye. That means you can get a brown, gray, or even charcoal-colored roof that performs significantly better than a traditional roof of the same color.
Finding Rated Products
The Cool Roof Rating Council (CRRC) is the independent nonprofit that tests and rates roofing products for reflectance and emittance. Their online Rated Products Directory is the standard tool for finding materials that meet California’s code requirements. Every rated product gets a CRRC label showing its tested values, which you can compare against the minimums for your climate zone. Builders use this directory to demonstrate code compliance, and you can use it to compare products when getting quotes from contractors.
Energy Savings You Can Expect
The energy savings from a cool roof vary depending on the building, climate, and how much air conditioning you use, but the numbers from California monitoring studies are significant. A Sacramento retail store cut air conditioning energy use by 52 percent after switching to a cool roof. A school in San Marcos, near San Diego, saw 17 to 18 percent savings. Two monitored commercial buildings in the state showed 12 to 18 percent reductions. In a study of portable classrooms in Sacramento, cooling energy dropped 46 percent and peak electrical demand fell 20 percent.
The biggest percentage savings tend to show up in smaller, lightly insulated buildings with a lot of roof area relative to their floor space, like single-story retail stores and schools. A well-insulated two-story home will see more modest savings in percentage terms, but the reduction in peak demand on the hottest days still matters for both your electricity bill and grid reliability.
Cooling California’s Cities
Cool roofs aren’t just about individual energy bills. They’re a tool for fighting the urban heat island effect, where dense neighborhoods with dark surfaces trap heat and run several degrees hotter than surrounding areas.
A Berkeley Lab study modeled what would happen if every building in California’s most populated regions adopted cool roofs by 2050. The results were striking: annual heat wave exposures (each instance a person experiences a heat wave) would drop from an estimated 80 million to 45 million. Focusing on the San Francisco Bay Area, Los Angeles, San Diego, and Sacramento alone, cool roofs could prevent 35 million heat wave exposures per year.
There’s one important limitation. Cool roofs reduce daytime temperatures when they’re actively reflecting sunlight, but they don’t directly cool the air at night. What they do is reduce the total amount of heat cities absorb during the day, which indirectly lowers how much heat buildings and streets release overnight.
Rebates and Financial Incentives
Several California utility programs offer rebates to offset the cost of installing a cool roof. The Energy Upgrade California program, a collaboration between state agencies, utilities, and local governments, provides rebates for energy-efficient home improvements including cool roofs in PG&E and Southern California Edison service areas. The Los Angeles Department of Water and Power runs its own cool roof rebate program. Availability and amounts change over time, so check your specific utility’s rebate page before starting a project. Products with a CRRC rating are typically required to qualify.