Title 24 Re-Roofing and Cool Roof Requirements
Replacing more than 50 per cent of a home’s roof surface is an alteration under §150.2(b)1I. A steep-sloped roof in climate zones 4 and 8 to 15 then needs a cool roof product unless an exception applies, and a low-sloped roof needs one in zones 4 and 6 to 15, plus R-14 continuous insulation in most zones.
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What brings a re-roof into scope
Section 150.2(b)1I covers replacing the exterior surface of an existing roof, including laying a new surface over the old one. Its cool roof and insulation rules apply where more than 50 per cent of the roof is being replaced. Changing material does not make it a repair: the compliance manual treats replacing wood shakes with asphalt shingles as an alteration.
Slope decides which rule applies. Section 100.1 defines a low-sloped roof as one with a rise of less than 2 in 12, and a steep-sloped roof as 2 in 12 or more. A house with both meets each rule on its own portion of the roof.
Steep-sloped roofs
In climate zones 4 and 8 to 15, new roofing needs an aged solar reflectance of at least 0.20 and a thermal emittance of at least 0.75, or a solar reflectance index (SRI) of at least 16. The code treats any of these as equivalent, so no cool roof product is needed:
- a ceiling insulated to R-38 or more, or an assembly U-factor of 0.025 or lower
- an attic radiant barrier meeting §150.1(c)2, not installed directly above spaced sheathing
- in zones 2, 4, 9, 10, 12 and 14, no ducts in the attic
- R-2 or more of continuous insulation above or below the roof deck
Roof area under building-integrated solar panels is exempt, and so is any roof construction weighing at least 25 pounds per square foot.
Low-sloped roofs
In zones 4 and 6 to 15, new roofing needs an aged solar reflectance of at least 0.63 and a thermal emittance of at least 0.75, or an SRI of 75. Table 150.2-E lets roof deck insulation stand in for reflectance: in zones 6 and 7, R-2 allows a reflectance of 0.60 and R-10 removes the requirement, while in zones 2, 4 and 8 to 15 the same steps run from R-16 to R-24.
A low-sloped re-roof also brings insulation under Table 150.2-F: R-14 continuous insulation, or a roof assembly U-factor of 0.039, in zones 1, 2, 4 and 8 to 16, and none in zones 3 and 5 to 7. It is not needed where the roof already has R-10 continuous insulation, or, in zones 1, 2, 4 and 8 to 10, where it already reaches U-0.056 or has R-19 between the rafters against the deck. Where rooftop equipment or a parapet would leave too little flashing height, the insulation may drop to R-4, and tapered insulation may average out.
Attics and vaulted ceilings
A steep-sloped re-roof over a vented attic carries no insulation requirement of its own. The attic rules in §150.2(b)1J, with R-49 in most zones, start only when the ceiling below is altered, for example by adding insulation, or a new duct system goes in the attic; they are on Title 24 insulation requirements. A rafter roof is different. The compliance manual treats it as altered once the space between the framing becomes accessible, as it does when the sheathing comes off, and the mandatory minimum of R-19 then applies.
Rated products only
Under §110.8(i), aged solar reflectance and thermal emittance must be certified and labelled through the Cool Roof Rating Council. An unrated product takes a default reflectance of 0.08 for asphalt shingles or 0.10 for other roofing, with an emittance of 0.75, which fails the steep-slope minimum. SRI is calculated from the aged reflectance. An ENERGY STAR listing is not enough, and on integrated solar roofing only the active PV area is exempt.
A new home has a narrower cool roof rule under §150.1(c)11: steep-sloped roofs in zones 10 to 15 and low-sloped roofs in zones 13 and 15. It is part of the new home Title 24 report.
Documenting it
A prescriptive re-roof goes on the alterations Certificate of Compliance. The Energy Commission lists CF1R-ALT-05-E for alterations that need no field verification and CF1R-ALT-01-E for prescriptive alterations generally. Where SRI is used, the SRI worksheet CF1R-ENV-04-E goes with it, and a radiant barrier claimed as the exception is recorded by the installer on CF2R-ENV-04-E. If the roof cannot meet the prescriptive values, the performance approach can trade it against other measures. Your climate zone decides which rules apply.
Other Residential Projects
- New Home Title 24 Report
- Does a Kitchen Remodel Need Title 24?
- Does a Bathroom Remodel Need Title 24?
Frequently Asked Questions
Only if more than half the roof is replaced and the home is in a listed zone: 4 and 8 to 15 for a steep-sloped roof, 4 and 6 to 15 for a low-sloped one. A steep-sloped roof is excused if, for example, the ceiling already has R-38 or the attic has a qualifying radiant barrier.
The reflectance a roofing product is rated to keep after three years of weathering, certified through the Cool Roof Rating Council. The code’s minimums are written against the aged value, not the initial one.
Not on a steep-sloped roof over a vented attic. A low-sloped re-roof needs R-14 continuous insulation in zones 1, 2, 4 and 8 to 16, unless the roof already meets one of the exceptions in §150.2(b)1I.
No. The compliance manual treats replacing a regulated component, such as the roof covering, as an alteration rather than a repair, even when the new material differs from the old.