IRC R316 requires a thermal barrier between spray foam and the occupied space. In living spaces, that is typically 1/2-inch gypsum drywall. In attics and crawl spaces, code allows specific intumescent paint coatings (DC315 is the dominant Cincinnati-area product) sprayed over the foam at the manufacturer-specified thickness.
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The IRC R316 thermal-barrier requirement exists because spray polyurethane foam combusts at 400-500F if exposed to direct flame, releasing carbon monoxide and other toxic gases. The thermal barrier gives fire response time and limits toxic-smoke generation. Two compliant approaches in residential construction. (1) Gypsum drywall: 1/2-inch standard or 5/8-inch Type X for higher fire rating. Universal acceptance from inspectors. Standard in any finished living space (basement family rooms, finished attics being converted to bedrooms). (2) Intumescent paint coatings: specific products tested and listed for use over spray foam in unfinished applications (attics, crawl spaces, garages). DC315 by International Fireproof Technology is the dominant Cincinnati-area product. Applied by spray at the manufacturer-specified dry-film thickness (typically 0.014 inches over open-cell, 0.011 inches over closed-cell, but verify the spec sheet for the specific product). Cost is roughly $0.40-$0.80 per square foot installed. When inspectors push back on intumescent coatings (rare but happens in some Northern Kentucky jurisdictions): drywall is the universal fallback. The choice for a Cincinnati homeowner. Attics: DC315 or equivalent intumescent paint, applied as part of the foam-project scope. Crawl spaces: DC315 is standard; some installers prefer mineral-fiber blanket over foam as a belt-and-suspenders approach. Garages: code requires 5/8-inch Type X drywall regardless because garage spaces are treated as fire-risk areas. Conditioned basements and finished attic spaces: 1/2-inch drywall as part of the normal finishing scope. Code-enforcement variance across Cincinnati metro. Cincinnati Building Department and Hamilton County Building Department both accept DC315 with manufacturer documentation. Butler County and Warren County follow the same convention. Clermont County occasionally requires additional verification for intumescent products; verify with the local jurisdiction at permit time. Northern Kentucky counties follow IRC adoption with some variation; Campbell and Kenton are generally lenient, Boone has been stricter on intumescent acceptance in recent years. Asking the installer to verify thermal-barrier compliance for the specific local jurisdiction at quote time prevents post-install inspection surprises.