Chapter 15 — ROOF ASSEMBLIES AND ROOFTOP STRUCTURES
1508 Roof Insulation — 2025 California Building Code
California Building Code (Title 24, Part 2) · 2025 edition · updated 2026-09-25 · California
CBSC: official editions, supplements and errata
Italicized text is a California amendment to the model code, as printed in the official publication.
Cite as: 2025 California Building Code (Title 24, Part 2) § 1508 · Effective January 1, 2026 · Official source: Building Standards Commission
[BF] 1508.1 General. The use of above-deck thermal insulation shall be permitted provided that such insulation is covered with an approved roof covering and passes the tests of NFPA 276 or UL 1256 when tested as an assembly.
Exceptions:
- Foam plastic roof insulation shall conform to the material and installation requirements of Chapter 26.
- Where a concrete or composite metal and concrete roof deck is used and the above-deck thermal insulation is covered with an approved roof covering.
[BF] 1508.2 Material standards. Above-deck thermal insulation board shall comply with the standards in Table 1508.2.
[BF] TABLE 1508.2—MATERIAL STANDARDS FOR ROOF INSULATION
| MATERIAL | STANDARD |
|---|---|
| Cellular glass board | ASTM C552 or ASTM C1902 |
| Composite boards | ASTM C1289, Type III, IV, V or VII |
| Expanded polystyrene | ASTM C578 |
| Extruded polystyrene | ASTM C578 |
| Fiber-reinforced gypsum board | ASTM C1278 |
| Glass-faced gypsum board | ASTM C1177 |
| High-density polyisocyanurate board | ASTM C1289, Type II, Class 4 |
| Mineral fiber insulation board | ASTM C726 |
| Perlite board | ASTM C728 |
| Polyisocyanurate board | ASTM C1289, Type I or II |
| Wood fiberboard | ASTM C208, Type II |
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