Unvented roof with spray foam — closed-cell flash, fill, and the thermal barrier

Closed-cell sprayed against the deck makes an unvented, conditioned attic (no soffit/ridge vents). Two code must-dos: the flash coat must hit the R806.5 condensation-control minimum for your zone, and foam in living space needs a ½″ gypsum thermal barrier.

A roof assembly section showing spray foam used to make an unvented, conditioned attic. Closed-cell foam is sprayed against the underside of the roof deck as a flash coat, then the cavity is filled to the total R-value with open-cell foam or batt between the rafters. Because the foam is at the roofline, the attic is inside the thermal envelope and the roof has no soffit or ridge vents. Two code requirements: the closed-cell flash must meet a minimum R-value for condensation control under IRC R806.5 (about R-15 in climate zone 4 up to R-35 in zone 8), and any foam in occupied space must be covered by a 15-minute thermal barrier such as half-inch gypsum board. — Source: IRC R806.5 (unvented roofs); NFPA 275 / IRC R316 (thermal barrier)

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A roof assembly section showing spray foam used to make an unvented, conditioned attic. Closed-cell foam is sprayed against the underside of the roof deck as a flash coat, then the cavity is filled to the total R-value with open-cell foam or batt between the rafters. Because the foam is at the roofline, the attic is inside the thermal envelope and the roof has no soffit or ridge vents. Two code requirements: the closed-cell flash must meet a minimum R-value for condensation control under IRC R806.5 (about R-15 in climate zone 4 up to R-35 in zone 8), and any foam in occupied space must be covered by a 15-minute thermal barrier such as half-inch gypsum board.

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    <img src="https://remodelcalculators.com/api/figure-embed/spray-foam-unvented-roof" alt="A roof assembly section showing spray foam used to make an unvented, conditioned attic. Closed-cell foam is sprayed against the underside of the roof deck as a flash coat, then the cavity is filled to the total R-value with open-cell foam or batt between the rafters. Because the foam is at the roofline, the attic is inside the thermal envelope and the roof has no soffit or ridge vents. Two code requirements: the closed-cell flash must meet a minimum R-value for condensation control under IRC R806.5 (about R-15 in climate zone 4 up to R-35 in zone 8), and any foam in occupied space must be covered by a 15-minute thermal barrier such as half-inch gypsum board." width="800" height="480" style="width:100%;height:auto;border:0" loading="lazy">
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    Diagram: <a href="https://remodelcalculators.com/construction-diagrams/spray-foam-unvented-roof" target="_blank" rel="noopener">Unvented roof with spray foam — closed-cell flash, fill, and the thermal barrier</a> — courtesy of <a href="https://remodelcalculators.com" target="_blank" rel="noopener">RemodelCalculators.com</a>
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