To calculate how much insulation you need, you will have to take into account: the area of the house you are insulating, your local climate, how much pre-existing insulation you have (if any), and the type of insulation you have or would like to install.

Main areas to check for insulation include finished and unfinished attics, exterior and basement walls, walls between heated and unheated spaces (such as those between your house and garage), and floors above unheated areas (such as those above crawlspaces and unheated garages).

The ideal R-value you will need to achieve depends on the area of your house and your region. According to the U.S. Department of Energy, ideal R-values range from R-30 to R-60 for attics, from R-13 to R-30 for floors, and from R-13 to R-21 for wall cavities. To figure out the recommended R-values for your particular application and climate, visit the DOE’s website at www.energy.gov or contact your local home improvement center or insulation retailer.

Follow the steps below to calculate how much insulation you will need to add to areas that already have some type of insulation:

1) To check for and measure insulation in a wall, turn off the electricity to your home, unscrew an electrical outlet cover, and insert a hanger into the open space. Use this probe to measure the depth of your insulation as well as to pull out and inspect the type of insulation you have (you may need to fashion your hanger into a slight hook to remove some material). You can drill a small hole into areas without an accessible outlet cover (such as between a floor and ceiling) to obtain your measurements. In an unfinished attic, merely slip a ruler between a floor joist and the existing insulation to figure out the depth of the material.

2) Next, multiply the depth of your existing insulation (in inches) by the R-value per inch for the type of insulation that you have; you can check with your home improvement retailer if you are unsure about the R-value per inch of your material. The resulting number is the total R-value of your existing insulation.

3) Now, subtract the total R-value of your existing insulation from the ideal R-value you wish to achieve. This difference represents how much R-value you will need to add to attain the recommended value.

4) Finally, divide this number by the R-value per inch of the insulation you plan to install. This figure tells you how many inches of additional insulation you will need.