ADU Cool Roof Requirements by Climate Zone
A new detached ADU needs a cool roof only in zones 10 to 15 for a steep-sloped roof and in zones 13 and 15 for a low-sloped roof: aged solar reflectance of 0.20 steep or 0.63 low, with thermal emittance of 0.75. Zones 1 to 9 and 16 have no requirement for new construction, though a re-roof can add one.
- Choose your report
- Upload your plans
- Pay securely
- Permit-ready report by email
Zone sets by project type
- New detached ADU: steep-sloped in zones 10 to 15, low-sloped in zones 13 and 15.
- Attached ADU or garage conversion treated as an addition: the same zones for roofing it installs, but an addition of 300 square feet or less is exempt.
- Existing building with more than 50 percent of its roof replaced: steep-sloped in zones 4 and 8 to 15, low-sloped in zones 4 and 6 to 15.
Zones 4, 8 and 9 reach the steep-slope rule only through a re-roof.
What counts as steep or low
A roof rising 2 in 12 or more is steep-sloped; anything flatter is low-sloped. A flat-roofed ADU in zone 13 or 15 needs 0.63 reflectance, while a gabled one in the same zone needs 0.20. Reflectance and emittance come from a Cool Roof Rating Council label, or an SRI of 16 steep and 75 low. An unrated product defaults to 0.08 reflectance (asphalt shingles) or 0.10 (other roofing), which fails the steep-slope minimum, and ENERGY STAR does not substitute.
Exceptions that matter on an ADU
Roof area under building-integrated solar panels is exempt, and so is any roof construction weighing at least 25 pounds per square foot. Tile is not automatically exempt: the manual lists its tile roof assemblies at 10 pounds per square foot. In a re-roof, a steep-sloped roof is treated as equivalent if the ceiling has R-38 or more, if the attic has a radiant barrier, or if there is R-2 of continuous insulation at the deck. In zones 4, 9, 10, 12 and 14 having no ducts in the attic also counts, which suits a ductless ADU.
On a larger addition the manual points to the performance method to trade the roof requirement against other features. The re-roof rules are explained on the re-roofing page, the product label on cool roof shingles, and the insulation beneath on ADU attic insulation. Find your zone on the climate zones page and order from the ADU page.
Common Title 24 Questions
- Do ADUs need Title 24 in California?
- What plans are needed for an ADU Title 24 report?
- How much does an ADU Title 24 report cost?
- How long does an ADU Title 24 report take?
- Does a garage conversion ADU need Title 24?
- Does a JADU need a Title 24 report?
Frequently Asked Questions
Additions of 300 square feet or less are exempt from the roofing requirement under Exception 1 to Section 150.2(a). Above that, the zone and slope rules apply.
For a new ADU they do not. A re-roof of more than half an existing roof can bring a requirement in zones 4 and 6 to 9 for low-sloped roofs, and in zones 4, 8 and 9 for steep-sloped ones.
Explore ADU and JADU
- ADU Duct Leakage Testing: When Is It Required?
- ADU Electric-Ready Requirements for Gas Appliances
- ADU Heat Pump Requirements in California for 2026 Permits
- ADU Heat Pump Water Heater Requirements
- Does an ADU Need HERS Registration?
View all ADU and JADU guides → · Permits and Compliance · Title 24 guide