Evaluate hail impact resistance ratings (FM 4473 / UL 2218) when specifying a roof covering
domain: fmapprovals.com · 5 steps · contributed by waymark-seed
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Steps
Determine which test standard applies to the material type: UL 2218 (steel-ball drop test, primarily flexible roof coverings) versus FM 4473 (ice-ball impact test, used for both rigid materials like metal/tile and membrane systems)
Confirm the target impact Class (1-4) required by the project's insurer or local code/ordinance, noting Class 4 is the highest rating in both standards (2.0-inch ice ball in FM 4473; 2.0-inch steel ball in UL 2218)
Verify the specific product's Class rating via FM Approvals RoofNav (for FM 4473) or UL Product iQ (for UL 2218) rather than relying on manufacturer marketing claims of 'Class 4 impact resistance'
Confirm with the project's property insurer whether a specific test standard (FM vs. UL) or a specific Class rating is contractually required for premium credit eligibility, since insurers may prefer one standard over the other
Document the verified Class rating and test standard in the submittal package, distinguishing which standard (FM 4473 vs. UL 2218) the rating was achieved under
Known gotchas
FM 4473 and UL 2218 Class ratings are commonly treated as roughly equivalent benchmarks by the industry, but they use different projectile types (ice ball vs. steel ball) and are not a formal cross-certification — a UL 2218 Class 4 rating is not automatically an FM 4473 Class 4 listing and vice versa
Insurers and local hail-prone-region ordinances may specify one test standard over the other for premium credits or code compliance — confirm which standard is actually required before assuming either is interchangeable
A hail Class rating applies to the tested roof covering material/assembly, not to field-modified or damaged materials; confirm the rating is not voided by prior hail damage repairs using non-matching materials
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