What R-Value Can You Expect from Spray Foam Roofing?

Spray polyurethane foam provides R-6.5 per inch — the highest R-value per inch of any roofing insulation available. Here's what that means in practice.

R-Value by Thickness

1 inch = R-6.5. 1.5 inches = R-9.75. 2 inches = R-13. 3 inches = R-19.5. 4 inches = R-26. These values are consistent across temperature ranges, unlike polyiso board which loses R-value significantly in cold weather.

Comparison to Other Roofing Insulation

Polyiso board: R-6 per inch (nominal), but drops to R-4–4.5 in cold climates. EPS board: R-4 per inch consistently. XPS board: R-5 per inch consistently. Spray foam: R-6.5 per inch, consistent across temperatures. Foam provides the best insulation performance in all conditions.

What R-Value Does Your Building Need?

ASHRAE Zone 5 (Ohio, Pennsylvania, etc.) requires R-30 for new construction roofs. To achieve R-30 with spray foam, approximately 4.6 inches are needed. Many foam restoration projects apply 2–4 inches, achieving R-13 to R-26 — still far superior to the near-zero insulation value of most existing single-ply membranes.

Energy Savings Impact

The energy savings from improved roof insulation depend on climate, building use, and existing insulation levels. Buildings transitioning from poorly insulated or uninsulated roofs typically see the most dramatic HVAC cost reductions — sometimes 20–30% in heating and cooling costs in extreme climates.