# §110.10: Cool roof requirements
What it requires
A "cool roof" is a roofing assembly with high solar reflectance (sends short- wave radiation back to the sky) and high thermal emittance (sheds long-wave heat once warmed up). For residential, the §110.10 mandatory threshold by slope:
- Low-slope (≤ 2:12) roofs in CZ13, CZ15: aged solar reflectance ≥ 0.63, thermal emittance ≥ 0.75 (or aged SRI ≥ 75).
- Steep-slope (> 2:12) roofs in CZ10–15: aged solar reflectance ≥ 0.20, thermal emittance ≥ 0.75 (or aged SRI ≥ 16).
The product carries a CRRC-rated label that the AHJ field inspector verifies at rough-in.
When it applies
- CZ10, CZ11, CZ12, CZ13, CZ14, CZ15, the hot climate zones.
- Newly constructed residential.
- Re-roofs where the existing assembly is replaced (re-roof triggers can be subtle, see §150.2(b)).
- Additions where ≥40% of the existing roof area is replaced.
How we use it
When your project's CZ is one of CZ10–15, we apply the cool-roof construction in EXT_ROOF_CONSTRUCTIONS automatically. The cool-roof assembly conflicts with the Title 24 Rule 856 expectations for a radiant barrier, so the model also suppresses RB in those zones, both the prescriptive baseline and the HP- Envelope option honor the suppression, with a "RB suppressed per Rule 856" note on the CF1R.
Common gotchas
- Cool-roof products vary widely by color, dark "cool-roof-rated" tiles exist but the SR value is below the §110.10 threshold for steep-slope in CZ10–15.
- Stand-alone radiant barriers under a cool-roof assembly cause compliance failures on the standard-design comparison.
- Re-roof projects in CZ10–15 trigger cool-roof requirements even when the homeowner just wanted to swap shingles, most contractors don't price for this and the AHJ catches it at final.