Attic Insulation

Why do attics need more insulation?

In the summer, the temperature in a typical Georgia attic can reach 140 degrees or more. In the winter, the same attic will usually come close to matching the outside temperature. Building scientists and code officials have come to realize over the years that the attic is a critical energy boundary and have increased the amount of insulation required.

Years ago, building codes required as few as 3½ inches of attic insulation. In the late 1970s, five to eight inches of attic insulation were common. Now the minimum amount of attic insulation for new construction is eight to 13 inches, depending on the type of insulation used.

What is the "R" value of your attic insulation?

The term "R-value" is a way of expressing the capacity of different materials to resist heat. The R-value of your attic insulation can be determined if you know the type of insulation and its depth.

Typically, in the Jackson EMC area, attic insulation is either fiberglass batts, blown-in fiberglass or blown-in cellulose. Fiberglass batts are thick sheets of insulation usually 15 inches or 23 inches wide, 8 feet or more in length and pink or yellow in color. They vary in thickness. Individual pieces of blown-in fiberglass are typically the size and consistency of cotton balls and are usually pink, yellow or white. Blown-in cellulose is made of ground up newspapers treated with boric acid. It is grayish in color.

You can get a sample of your attic insulation from around your attic access. Use the descriptions mentioned above to determine your specific type of attic insulation.

Once you determine the type of insulation you have in your attic, you are now ready to measure the depth of your attic insulation.

First, find an area of your attic where the insulation looks fairly uniform in depth. Avoid areas right next to the attic opening or next to the ductwork. Take a measuring device (preferably 18 inches or longer) and insert it into the insulation until it comes in contact with the ceiling. Read the measurement at the top of the insulation. Repeat this procedure two more times in different locations. Average the results of the three measurements to determine the average depth of your insulation.

Now that you know the type of attic insulation and its average depth, you can determine its R-value. Multiply the depth in inches by the "R-value per inch" for the particular type of insulation in your attic:


R-value per inch - 2.5


R-value per inch - 3.1

This will give you the total R-value of your attic insulation.

Here's an example. Lets say you have pink fiberglass blown-in insulation in your attic. You take the three depth measurements in your attic and come up with an average depth of 5 inches. The R-value per inch for blown in fiberglass is 2.5. Multiply 2.5 by 5 inches and you get an R-value of 12.5.

To add or not to add: that is the question

Adding extra attic insulation may not always be cost effective. A good rule of thumb is this: if you have an R-19 or less in your attic, it will probably be worth the expense to go ahead and add the extra insulation. And if you decide to add the extra insulation, it doesn't cost that much more to go above to an R-30 rating as long as your ceiling can handle the weight. An insulation contractor can help you with this and other specifics of the project. For more information, see the insulation industry's Web site at