Some shingle manufacturers reduce warranty terms on hot-roof (unvented) assemblies where the roof deck temperature can run higher than a vented assembly. Read your shingle warranty carefully or call the manufacturer before specifying closed-cell at the roof deck. Most major shingle warranties still apply but with reduced years.
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Most asphalt shingle manufacturers (GAF, Owens Corning, CertainTeed, Tamko, Atlas) maintain their material warranty on roofs over unvented (hot-roof) assemblies created by closed-cell spray foam at the roof deck. The warranty terms typically reduce from the standard 25-30 year limited warranty to a 10-20 year warranty depending on the specific manufacturer and product line. Read the warranty document or call the manufacturer technical line before signing the foam install if shingle warranty protection matters to you. Two specific warranty patterns to watch for. (1) "Ventilated assembly required" clauses: some Class A shingles specify ventilation as a condition of warranty; verify before spec-ing a hot-roof assembly. (2) "Extended-life" warranty tiers: GAF Golden Pledge, Owens Corning Platinum, and similar premium-tier warranties often have stricter assembly requirements than standard warranties. The standard warranty usually applies; the premium tier sometimes does not. Cincinnati installer practice: our team flags the shingle warranty question during the on-site assessment when the homeowner is considering closed-cell at the roof deck. If the homeowner intends to file the warranty registration or sell soon and wants the strongest warranty position, we either (1) recommend open-cell at the attic floor instead, preserving the vented assembly, or (2) spec a heat-tolerant shingle product designed for unvented assemblies (Atlas Pinnacle Pristine and similar are explicitly marketed for hot-roof use). The energy and comfort benefits of conditioned-attic closed-cell foam usually outweigh the warranty trade-off, but it should be a documented choice rather than an accidental one. Cincinnati shingle warranty practical reality: most pre-2010 Cincinnati shingle warranties have already expired or are close to expiry, so the trade-off only applies to recent re-roofs. If your shingles are older than the warranty period, the question is academic.