Does an ADU addition or garage conversion need a cool roof?

Sometimes. The CEC's 2025 ADU FAQ says ADU additions must meet the cool roof requirements of Section 150.1(c)11, but only for certain roof types in certain climate zones: steep-sloped roofs in climate zones 10 through 15, and low-sloped roofs in climate zones 13 and 15. Additions of 300 square feet or less are exempt.

What a "cool roof" means in the code

A cool roof uses roofing products rated to reflect sunlight and shed heat. The code sets minimums for aged solar reflectance and thermal emittance, or an equivalent Solar Reflectance Index (SRI):

• Steep-sloped roofs, climate zones 10 to 15: aged solar reflectance of at least 0.20 and thermal emittance of at least 0.75, or an SRI of at least 16.
• Low-sloped roofs, climate zones 13 and 15: aged solar reflectance of at least 0.63 and thermal emittance of at least 0.75, or an SRI of at least 75.

Outside those climate zones and roof types, Table 150.1-A sets no prescriptive cool roof requirement.

Exceptions

• Small additions: Exception 1 to Section 150.2(a) exempts additions of 300 square feet or less.
• Heavy roofs: roof constructions weighing at least 25 pounds per square foot, such as some tile, are exempt.
• Building-integrated solar: building-integrated PV panels and building-integrated solar thermal panels are exempt from the rating requirement.
• Performance path: a performance model can trade the cool roof against other measures.

Garage conversions

A garage conversion is an addition, because it conditions space that wasn't conditioned before. The CEC's ADU training describes the addition roofing requirement as applying to the new portion of roof. If you keep the existing garage roof, ask plan check how they apply it. If you're replacing the roof as part of the project, the alteration rules for re-roofing in Section 150.2(b) can also apply. Your Title 24 report should address the roof either way.

New detached ADUs

A newly constructed ADU follows the same Table 150.1-A roofing requirements in the same climate zones, along with the other new-construction measures.

Practical tips

• Confirm your climate zone by parcel address before choosing roofing, especially near zone boundaries.
• Pick a product listed with the Cool Roof Rating Council at the aged ratings you need. Initial ratings aren't enough.
• Note the roof slope on the plans so plan check applies the right category.

What this means for your MEP plans and Title 24 report

The CF1R lists the roofing requirement, or the exception used, and the architectural roof notes should match it. Because roof color and attic conditions affect cooling loads, the mechanical equipment sizing uses the same assumptions. See Title 24 in climate zone 15, why your climate zone matters, and the ADU Title 24 guide.

Sources: energy.ca.gov, energy.ca.gov, energy.ca.gov.