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Below Deck Spray Foam Insulation for Existing Roofs

Guide describing how to add spray foam insulation to the underside of the existing roof deck as part of the conversion of a vented attic to an unvented, insulated attic.

Spray foam insulation was installed on the underside of the roof deck and on gable end attic walls to create an unvented attic

Publication Date

Fri, 10/15/2021 - 12:00

Wrong – Roof underlayment is not fully adhered and roof deck seams are not sealed so roof is susceptible to high-wind events

Right – Roof underlayment is fully adhered and roof deck seams are sealed so roof is resistant to high-wind events

Detail of an unvented cathedralized attic showing air-impermeable spray foam insulation plus batt insulation installed on the underside of the roof deck.

Sloped roof with cavity spray foam insulation sprayed on underside of roof deck and covered with sprayed-on thermal or ignition barrier coating.

Publication Date

Fri, 05/01/2015 - 12:00

Right – Closed-cell polyurethane foam is sprayed on the underside of the roof deck to provide structural connections and seal seams in the sheathing to increase wind resistance

Right - This new sealed attic has 5.5 inches (R-20) of spray foam insulation along the underside of the roof deck providing a conditioned attic space for the heating and cooling ducts.

Unvented Insulated Sloped Roofs

Guide describing construction of sloped roofs that are unvented and are insulated above the roof deck.

Unvented Attic Insulation

Guide describing methods for insulating an unvented attic along the roof line.

Attic Air Sealing, Insulating, and Ventilating for Ice Dam Prevention

Information guide describing proper attic air-sealing, insulation, and ventilation to combat ice dam formation on roofs in cold climate zones.

Vented versus Unvented Attic

Guide describing options for designing and locating the thermal boundary at either the attic floor or along the roof line in new and existing homes.

Air Sealing, Insulating, and Venting Attics and Roofs to Reduce Heat Gain

Information guide providing links to guides describing specific ways to air-seal, insulate, and ventilate attics and roofs to minimize heat gain in new and existing homes.

Roof/Attic to Exterior Wall Air Control Upgrade

Guide outlining how to retrofit an exterior wall and/or attic to provide continuous air sealing.

Flashing of Roof-Wall Intersections in Existing Homes

Guide describing how to install and properly integrate flashing at the intersection of the wall and roof on an existing home.

Flashing of Penetrations in Existing Roofs

Guide describing how to provide a continuous water control layer across the roof assembly by sealing all penetrations for pipes, vents, etc. in existing roofs.

Attic Eave Minimum Insulation

Guide providing guidance on insulating attic eaves in new and existing single-family homes and multifamily buildings.

Attic Knee Walls

Guide describing how to insulate and air-seal attic knee walls and floor joist cavities under knee walls.

Air Sealing Attic Access Panels/Doors/Stairs

Guide describing how to air-seal attic access panels, doors, and stairs to provide a continuous air barrier at the ceiling.

Taped Insulating Sheathing Drainage Planes

Guide describing techniques for installing insulating sheathing as a continuous drainage plane on walls.

Drainage Plane Behind Exterior Wall Cladding

Guide describing installation of a fully sealed continuous weather resistant barrier to provide a drainage plane to keep rainwater out of above-grade walls.

Air Sealed, Insulated Basements

Guide describing how to insulate a basement to improve the overall thermal performance of the building and provide more dry, usable conditioned space for home occupants and HVAC equipment.