Coating a Flat Roof: Title 24 Rules for Liquid-Applied Roof Coatings
A field-applied coating can qualify as the cool roof on a low-sloped roof, but it must cover the whole roof at the maker's mil thickness, pass the Table 110.8-C or ASTM tests, and carry a CRRC rating. Where 0.63 aged reflectance is required, the coating is held to a lower soiling credit than shingles.
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What the coating itself has to meet
Section 110.8(i)4 governs liquid products applied in the field as the top surface of a low-sloped roof, meaning a pitch under 2:12. The coating goes across the entire roof surface to the dry mil thickness or coverage the manufacturer recommends for that substrate. It must meet the physical-property table (Table 110.8-C) or the ASTM standard for its material: C836, D3468, D6083 or D6694. Exceptions: aluminum-pigmented asphalt coatings follow ASTM D2824 and D3805; cement-based coatings need at least 20 percent cement and ASTM C1583, D822 and D5870.
Why a bright initial number is needed
Every product used for reflectance credit must be rated by the Cool Roof Rating Council, and the packaging of a liquid coating must state that it meets Section 110.8(i)4. If the council lists only an initial value, the aged value is 0.2 plus the soiling resistance times (initial minus 0.2), and field-applied coatings use 0.65 where other products use 0.70. To reach an aged 0.63 a coating therefore needs an initial reflectance near 0.86. An uncertified product falls back to a default of 0.10, which fails.
When the 0.63 target applies
For a low-sloped roof, Section 150.2(b)1I applies when more than 50 percent of the roof is replaced, including adding a new surface layer on top of the existing one. In zones 4 and 6 to 15 the new product needs aged reflectance of 0.63 and thermal emittance of 0.75, or an SRI of 75. Roof-deck insulation can offset part of the reflectance (Table 150.2-E). Zones 1, 2, 4 and 8 to 16 also face Table 150.2-F, which calls for R-14 continuous insulation unless an exception such as existing R-10 applies.
Is a recoat a re-roof?
The residential rule never says recoat; the nonresidential rule names "replaced, recovered or recoated". Whether coating alone counts as a new surface layer is the building department's call. Ask before buying product.
See re-roof Title 24, cool roof requirements and when a roof triggers insulation. We prepare residential reports for roof jobs.
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
Its packaging must state that it meets Section 110.8(i)4, and the product must have a CRRC rating to count toward reflectance requirements.
Derive it from the initial value with the soiling resistance of 0.65 for field-applied coatings. An unrated product takes a default reflectance of 0.10, which fails 0.63.
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