This calculator is designed to help users quickly and accurately determine the total R-value of an exterior wall assembly. Simply follow the steps to build your wall and determine its r-value.

R-Value Calculator For Exterior Above-Grade Walls

Step 1: Choose Exterior Cladding



Step 2: Continuous Insulation


Step 3: Choose Sheathing


Step 4: Framing & Insulation


Step 5: Interior Finish

Step 6: Air Film

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Results:

Select components to see the breakdown.

Disclaimer and Limitations
The information provided by this calculator is intended solely as a general guide. While care has been taken to ensure the accuracy and reliability of the calculations, the results are based on averaged values and should not be considered a substitute for professional advice. Each wall assembly is unique, and many factors can affect its actual performance.

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Things You Should Know

What is R-Value?

R-value measures the resistance to heat flow through a material or assembly. The higher the R-value, the better the material or assembly insulates against heat transfer. It’s a critical factor in determining the energy efficiency of buildings.

R-value is expressed in units of square foot-hour per degree Fahrenheit per British Thermal Unit (BTU). This means it quantifies the amount of heat that a material can resist over a specific area, time, and temperature difference.

What’s the difference between R-Value and U-Value?

While R-value measures thermal resistance, U-value measures thermal conductivity—the rate at which heat flows through a material. R-value and U-value are inversely related, meaning higher R-values correspond to lower U-values. For most applications, R-value is used to evaluate insulation performance.

Calculating R-Value

To calculate the total R-value, simply add the individual R-values of all layers in the assembly. For example:
If drywall has an R-value of 0.45, insulation has 13, sheathing has 0.5, and siding has 0.65, the total R-value is:
( 0.45 + 13 + 0.5 + 0.65 = 14.6 ).

What is the ideal R-value for my area?

The ideal R-value depends on your location’s climate zone and is likely dictated by your local building code the International Energy Conservation Code (IECC).

What’s the difference between nominal R-value and effective R-value?

The nominal R-value is the listed thermal resistance of a material or insulation product—usually provided by manufacturers. It represents the material’s ability to resist heat flow in ideal conditions, without accounting for how it’s installed or what it’s installed alongside.

The effective R-value is a more realistic measure of a wall assembly’s performance. It accounts for all materials in the assembly and how they interact—including framing, air films, thermal bridging, and installation quality.

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