Cool Roof Requirements When Reroofing a House
A re-roof needs a cool roof product only when more than half the roof is replaced, the zone is on the list for the slope (steep: 4 and 8 to 15; low-sloped: 4 and 6 to 15) and no exception applies. The product then needs an aged solar reflectance of 0.20 on steep roofs or 0.63 on low-sloped ones.
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Four checks, in this order
Every cool roof rule for an existing house comes from Section 150.2(b)1I. Run these checks before the roofer orders material.
- Zone and slope. Steep means 2 in 12 or steeper, and low-sloped is flatter. Zones 1, 2, 3, 5 and 16 appear on neither list, so a re-roof there never needs a cool roof product. Find your zone first.
- Share of the roof. A new surface laid over the old one counts as replacing it. The Standards say "more than 50 percent", while the manual's worked answer says "50 percent or more", so ask the department about a job that lands on the line.
- Exceptions. A steep roof may skip the product with an R-38 ceiling or U-0.025, a qualifying attic radiant barrier, R-2 of continuous insulation above or below the deck, or, in zones 2, 4, 9, 10, 12 and 14, no ducts in the attic. Roof construction of 25 pounds per square foot or more, and area under building-integrated solar panels, are excused.
- The product. Steep roofs need an aged reflectance of 0.20 with an emittance of 0.75, or an SRI of 16. Low-sloped roofs need 0.63 with 0.75, or an SRI of 75. The figures must come from a Cool Roof Rating Council listing: an unrated asphalt shingle is assigned 0.08, which fails.
Low-sloped and mixed roofs
On a low-sloped roof, Table 150.2-E trades deck insulation for reflectance. In zones 4 and 8 to 15, R-16 allows 0.60 and R-24 removes the requirement; in zones 6 and 7 the steps run from R-2 to R-10. A house with both slopes meets each rule on its own portion, or goes to the performance method.
Where to go next
Insulation that a low-sloped re-roof adds is on the re-roofing page, and label reading is on cool roof shingles. Permit questions are on roof replacement permits. Insulation triggers are on roof replacement and insulation upgrades. Our residential Title 24 reports include re-roofs.
Common Title 24 Questions
- When is Title 24 required for a home?
- Does a remodel need Title 24?
- Does a room addition need Title 24?
- What plans are needed for a residential Title 24 report?
- How much does a residential Title 24 report cost?
- How long does a residential Title 24 report take?
Frequently Asked Questions
No. The Standards require the aged solar reflectance and thermal emittance to be certified through the Cool Roof Rating Council, and the compliance manual says an ENERGY STAR listing does not substitute.
The Standards say more than 50 percent, but the manual says 50 percent or more. Ask the building department which it applies, or plan for the stricter reading.
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