How to Calculate a Total Wall R-Value

Find out what materials make up the wall to be calculated. If you are building a new home or addition, this will be simple. If you are remodeling and want to know the R-value of an existing wall, look at an exposed section of wall and write down what materials it is composed of and in what thickness.

Look up all of your materials on an R-value table. Write down the R-value of each material. These numbers will be listed as either R-value per inch (as with insulation or siding) or as a total for the material (as with concrete blocks). If you are building a new house, the insulation will have an R-value printed on it. If this is the case, there is no need to look it up.

Multiply the number of inches, in decimal notation, of each material's thickness by its R-value.

Add together all of the sums obtained in Step 3. This number is the "clear wall R-value," which is the R-value of the wall without taking into account the studs and windows. It will likely be higher than a measurement that does take those factors into account, which is called the "whole wall R-value."

Determine the whole wall R-value quickly by entering your materials list into the whole wall R-value calculator maintained by the Oak Ridge National Laboratory for the U.S. Department of Energy. Keep your materials list handy and simply enter the values into the spaces provided. For this calculation, you should also know if the studs are made out of wood or metal. You can download the R-value calculator or use it online in an abridged form.