IRC R316 (adopted by the Ohio Residential Code) 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 Columbus-area product) sprayed over the foam at the manufacturer-specified thickness.
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The IRC R316 thermal-barrier requirement, adopted through the Ohio Residential Code, 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 Columbus-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 outlying jurisdictions): drywall is the universal fallback. The choice for a Columbus 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 Columbus metro. The Columbus Department of Building and Zoning Services and Franklin County both accept DC315 with manufacturer documentation. Delaware County and Licking County follow the same convention. Fairfield and Union counties occasionally require additional verification for intumescent products; verify with the local jurisdiction at permit time. Asking your installer to verify thermal-barrier compliance for the specific local jurisdiction at quote time prevents post-install inspection surprises.