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 insulation is measured in R-value per inch. 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 the 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 – and in cold-winter climates many attics are insulated to at least R-40.

Wall insulation is trickier to assess. 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 of 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.

John Krigger is a nationally recognized author of numerous energy efficiency books, including Surviving the Seasons, and Residential Energy: Cost Savings and Comfort for Existing Buildings. For more info, visit his website www.residental-energy.com.