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Ventilation air inlets ≥ 2 ft. above grade or roof deck in Climate Zones 1-3 or ≥ 4 ft. above grade or roof deck in Climate Zones 4-8 and not obstructed

Ventilation inlet does not terminate high enough above the roof deck

Unvented Conditioned Attic with Spray Foam Insulation Below Roof Deck

Guide describing a method for insulating an unvented attic by spraying foam insulation along the underside of the roof deck.

Ventilation inlet is not near any exhaust outlets/contamination sources and is at least 2 ft. above the roof deck

Ventilation inlet is too close to exhaust outlets and does not extend at least 2 ft. above the roof deck

The attic is sealed and insulated along the underside of the roof deck with 5.5 inches of polyurethane spray foam, providing conditioned space for the HVAC system.

Right – Flex ducts are properly supported with straps that don’t pinch the insulation; closed-cell spray foam will be applied to the underside of the roof deck of this hot-humid climate home to provide an insulated attic space for the HVAC ducts.

Publication Date

Thu, 09/30/2021 - 12:00

Controlling Moisture in Unvented Attics - Code Compliance Brief

Publication Date

May, 2017

The intent of this brief is to provide code-related information about controlling moisture in unvented attics by installing a vapor diffusion port/vent that would convey water vapor from an unvented attic to the outside when air-permeable insulation materials are installed and can be verified as being in compliance with the related codes and standards for residential construction. Providing consistent information to document compliance with codes and standards to all relevant parties responsible for verifying compliance (e.g., code officials, builders, contractors, designers, etc.) is expected to result in increased compliance and more timely, less challenging and more uniform plan review and field inspections.

Support at Intervals for Flex Ducts

Guide describing how to hang ducts with supporting straps or saddles to adequately support ducts so they do not sag and are not pinched or compressed in a manner that would cause damage to the ducts, the duct insulation, or the duct air barrier covering.

Ventilation air inlets ≥ 2 ft. above grade or roof deck in Climate Zones 1-3 or ≥ 4 ft. above grade or roof deck in Climate Zones 4-8 and not obstructed

Ventilation inlet does not terminate high enough above the roof deck

Unvented Conditioned Attic with Spray Foam Insulation Below Roof Deck

Ventilation inlet is not near any exhaust outlets/contamination sources and is at least 2 ft. above the roof deck

Ventilation inlet is too close to exhaust outlets and does not extend at least 2 ft. above the roof deck

The attic is sealed and insulated along the underside of the roof deck with 5.5 inches of polyurethane spray foam, providing conditioned space for the HVAC system.

Right – Flex ducts are properly supported with straps that don’t pinch the insulation; closed-cell spray foam will be applied to the underside of the roof deck of this hot-humid climate home to provide an insulated attic space for the HVAC ducts.

Controlling Moisture in Unvented Attics - Code Compliance Brief

Support at Intervals for Flex Ducts

Ducts Buried in Attic Insulation and Encapsulated

Ducts in Dropped Ceilings

Compact Air Distribution

Ducts in Raised Ceiling Sections