Title 24 cool roofs
Cool roof rules for a California reroof, explained
California's Energy Code asks some reroofs to use "cool" roofing: products that reflect more sunlight and shed heat. In the Bay Area the rule applies only in Climate Zones 4 and 12, and only when half or more of the roof is replaced. Here is how to tell whether it covers your house, and what the label has to show.
What is a cool roof?
A cool roof is roofing with high solar reflectance (it bounces back more of the sun's energy) and high thermal emittance (it gives off the heat it does absorb). The point is a cooler attic and less air-conditioning on hot days. It is a property of the product, measured in a lab, not a colour you pick by eye: some medium and darker shingles are rated cool, and some light ones are not.
The Energy Code measures both after three years of weathering, as "aged" values, or combines them into a Solar Reflectance Index (SRI). Products are rated by the Cool Roof Rating Council (CRRC) and carry a CRRC label with the numbers.
Does the rule apply to your reroof?
In the Bay Area it applies only when half or more of the roof is replaced on a house in Climate Zone 4 or 12, and the numbers it sets then depend on the roof's slope. Three questions decide it, according to the Bay Area Regional Energy Network's guide to the 2022 code:
- How much is replaced? Cool roof requirements are triggered when 50 percent or more of the roof is replaced. A smaller repair does not trigger them.
- Which climate zone is the house in? In the Bay Area, only Climate Zone 4 (parts of Santa Clara County) and Climate Zone 12 (parts of Alameda, Contra Costa and Solano Counties) carry the reroof cool roof rule. Coastal zones do not. Check your address on the California Energy Commission's climate zone tool.
- Is the roof steep or low-slope? Steep slope means a rise of more than 2 in 12; low slope means less. They have different numbers.
The numbers on the label
| Roof | Zones (reroofs) | Minimum aged solar reflectance | Minimum thermal emittance | Or minimum SRI |
|---|---|---|---|---|
| Steep slope (over 2:12) | 4 and 8–15 | 0.20 | 0.75 | 16 |
| Low slope (under 2:12) | 4 and 6–15 | 0.63 | 0.75 | 75 |
These are the single-family reroof values in the 2022 code as BayREN summarizes them, and the Cool Roof Rating Council's chart of the 2025 Energy Code lists the same steep-slope values for reroofs in Zones 4 and 8–15 (section 150.2(b)1Ii). Low-slope reroofs in most zones also carry roof insulation requirements, with their own exemptions.
Exemptions worth knowing
- Roof area covered by building-integrated solar panels or solar thermal panels is exempt; the rest of the roof still has to comply.
- Roofs weighing at least 25 pounds per square foot, such as some green roofs, are exempt.
- For steep-slope reroofs, BayREN's guide lists further exemptions, for example when there is a qualifying radiant barrier in the attic, or no ducts in the attic. Ask the roofer to check these against the code edition your permit falls under.
- Replacing less than half of the roof does not trigger the cool roof rule.
How compliance is shown
A reroof in California needs a building permit, and the Energy Code part is documented on the state's compliance forms for roofing alterations. The inspector looks for the CRRC label on the product, so ask your roofer to keep a label or wrapper from the delivery until the final inspection. If the product is chosen before the permit, check its CRRC listing first; changing products after the shingles arrive is expensive. The Energy Standards Hotline at (800) 772-3300 answers code questions.
Which code edition applies?
California updates the Energy Code every three years. The 2025 edition applies to permits applied for from January 1, 2026; earlier permits follow the 2022 rules. The reroof figures above are the same in both for single-family homes, but section numbers and some exemptions moved, so the city and the roofer should use the forms for your permit's edition. BayREN's guide is written for the 2022 code; the CRRC chart covers 2025.
What it means for the rest of the roof
Cool roofing is one part of a reroof, not the whole of it. Underlayment, flashing and ventilation still decide whether the roof keeps water out. Low-slope roofs on additions and garages are where the rule changes the most, because the 0.63 reflectance value usually means a white or very light membrane or coating. For the whole job, see roof replacement, and for the region, roof repair in the Bay Area.
Ask whether the cool roof rule applies to you
Tell us what the roof is doing, what it is made of if you know, and the city or ZIP. We call or email you back about it; the request is free and commits you to nothing.
Cool roof questions
Does my Bay Area city require a cool roof when I reroof?
Only if the house is in Climate Zone 4 or 12 and half or more of the roof is replaced. Look up your address on the Energy Commission's climate zone tool, then ask your building department or roofer to confirm, because a city can add local rules of its own.
Can I still choose a dark shingle?
Possibly. The steep-slope rule is a measured aged reflectance of at least 0.20 with emittance of 0.75, or SRI 16, not a colour. Several medium and some darker products are rated to meet it. Check the product's CRRC listing for your colour before you order.
What if solar panels cover part of the roof?
Area under building-integrated solar panels is exempt from the cool roof values, but the uncovered roofing must still comply when the rule applies. Ordinary rack-mounted panels sit above the roofing, so ask your roofer and the city how they treat the area beneath them.
Sources: BayREN, Residential Roofing: Guide to 2022 Energy Code Requirements (updated 2022-12-20); Cool Roof Rating Council, Chart of 2025 CA Energy Code Cool Roof Requirements (2025-12-04); California Energy Commission, Residential cool roof fact sheet (2022 code) and climate zone tool.