To calculate the R-value in insulation, determine the R-value of the specific insulating material. For multilayer installations, determine the R-values of each layer, and add the values together to get the total R-value of the system. The higher the R-value, the greater its insulating properties.

**Determine the R-value of each layer**Contact the manufacturer of each layer of insulation used to find out the R-value of each layer of material. When determining the precise R-value, measure the thickness of the material as well as its density, and report these figures to the manufacturer to gain accurate results.

**Add the various R-values**Add each of the R-values for each layer of material in place to determine the total R-value of the insulation. Add in the relative R-values of radiant reflective materials, which do not have actual R-values of their own but work by reflecting the heat from the radiant surfaces.

**Account for insulate space**Modify the R-values of the various materials according to the manufacturer's specifications. Spaces such as ceilings may have lower R-values for the insulating material, for example, because of other building materials providing heating bridges across the spatial area. The totals for the modified amounts are the actual R-values of the multilayered insulating materials.