Assessing Insulation

Assessing the insulation level in your home’s attic and walls is a straightforward process that can help you decide whether more insulation would be a cost effective improvement.

Your attic or ceiling insulation is the most important part of your home’s thermal boundary because it helps reduce heat gain in the summer as well as minimizing heat loss in the winter. To assess your attic insulation, locate the hatch or door that leads to your attic, and use a ladder if needed to get up where you can see the entire attic. Measure to see how many inches of insulation is installed, and decide what type of insulation you have. If you’re not familiar with the type of insulation, take a small sample to your local building supply store to ask for help in identifying it.

The effectiveness of your insulation is measured in R-value. The total R-value of your insulation depends both on its type and its depth. To determine the total R-value of your insulation, decide what type of insulation is installed, and multiply its rated R-value per inch times the number of inches installed. Cellulose loose-fill insulation, for example, is rated at about R-3.5 per inch. If your attic has 4 inches of cellulose, that’s 3.5 x 4 = R-14. Your attic insulation should be at least R-30 if you live in a mild climate, and in cold winter climates attics should be insulated to at least R-40 or more.

Wall insulation is trickier to evaluate. Try looking around the edges of an electrical outlet box. First turn the power off at your main electrical panel, then remove the outlet’s cover plate. Use a flashlight to peek around the edges of the box. You can also cut an inspection hole through the drywall in the back of a closet or other hidden location. Wall insulation should completely fill the wall cavity. Walls with no insulation or partial insulation can be re-insulated with loose-fill material that is blown through a tube inserted into the wall. This is job for professionals.

For more information, see The Homewoners Handbook to Energy Efficiency, or Chapter 4 of Residential Energy: Cost Savings and Comfort for Existing Buildings.

Type of Insulation

Fiberglass, blankets or loose-fill

Cellulose, loose-fill

Mineral wool, blankets of loose-fill

Foam board, white

Foam board, blue or pink


R-Value per Inch 2.9 – 3.5 3.5 3.0 3.8 5.0 6.5