Spray Foam Attic Insulation Guide

Spray foam attic insulation is one of the most effective ways to reduce building energy consumption, improve comfort, and eliminate moisture and air quality problems associated with poorly insulated and air-sealed attics.

Spray foam attic applications:

Attic floor (above ceiling): Open-cell foam applied between and over attic floor joists creates a continuous air barrier and insulation layer. Typical thickness: 5.5–9" of open-cell (R-19 to R-36). This approach leaves the attic space unconditioned and vented.

• Roof deck (conditioned attic / unvented attic):
• Foam applied to the underside of the roof deck creates an unvented, conditioned attic space that is part of the building's thermal envelope. This approach:
• Eliminates ductwork energy loss (ducts in conditioned space instead of the thermal boundary)
• Eliminates ice dams in cold climates
• Reduces moisture-related problems in humid climates
• Typically requires closed-cell foam or a combination of closed-cell and open-cell

Typical roof deck application: 2–3" closed-cell (R-13 to R-21) or 5.5–7" open-cell (R-19 to R-28). Building code requirements for roof deck insulation vary by climate zone.

Gable walls: Foam applied to gable end walls as part of an unvented attic enclosure.

Existing attic retrofit: Retrofitting an attic with spray foam typically requires removing existing blown insulation before application. The investment is higher than adding blown insulation, but the air sealing performance of spray foam is not achievable with blown products.

For contractors: Attic roof deck applications often require multiple lifts for closed-cell foam. Open-cell attic applications are typically faster and use more material per set due to the lower density.