Rigid insulation foam board attached to ceiling

[cevans (Chuck Evans, CMI)]

Here is your authoritative source. You’ll need to do your own research on the numbers for the styrofoam insulation that is installed, but it won’t meet the standard. You will also need to separately assess whether the material behind the insulation meets R302.6 Dwelling/garage fire separation.

R302.9 Flame spread index and smoke-developed index for
wall and ceiling finishes. Flame spread and smoke index for
wall and ceiling finishes shall be in accordance with Sections
R302.9.1 through R302.9.4.

R302.9.1 Flame spread index. Wall and ceiling finishes
shall have a flame spread index of not greater than 200.
[INDENT]Exception: Flame spread index requirements for finishes
shall not apply to trim defined as picture molds,
chair rails, baseboards and handrails; to doors and windows
or their frames; or to materials that are less than 1/28
inch (0.91 mm) in thickness cemented to the surface of
walls or ceilings if these materials exhibit flame spread
index values no greater than those of paper of this thickness
cemented to a noncombustible backing.[/INDENT]

R302.9.2 Smoke-developed index. Wall and ceiling finishes
shall have a smoke-developed index ofnot greater than
450.