R-Value & Insulation Calculator

Calculate the insulation R-value of your roof assembly and find how much insulation to add to meet energy code requirements.

Climate Zone

Current Attic Insulation Depth (inches)

Insulation Type

Attic Floor Area (sq ft)

Results

Visualization

How It Works

R-value measures thermal resistance — higher is better. The 2021 IECC energy code requires R-49 in the attic for zones 4-7 (most of the US north of Atlanta) and R-38 for zones 2-3. Most older homes have only R-11 to R-19 (3-6 inches). Adding insulation is one of the best energy upgrades: blown cellulose at R-3.5/inch is the best value for attic floors. Closed-cell spray foam at R-6.5/inch achieves more R-value in less depth and adds structural rigidity. In cold climates, air sealing (sealing gaps, penetrations, and bypasses) is equally important — the best insulation is useless if air blows through it.