To calculate how much insulation you need, you will have to take into account: the area of your house, your local climate, how much pre-existing insulation you have (if any), and the type of insulation you have or would like to install.
Follow the steps below to calculate how much insulation you will need to add to areas that already have some type of insulation:
1To 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.
2Next, 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.
3Now, 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.
4Finally, 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.
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