You should insulate your home when the following occurs:
>You have an older home and haven’t added insulation. Only 20% of homes built before 1980 are well insulated.
>You are cold in the winter or hot in the summer. Adding insulation creates a more uniform temperature and increases comfort.
>You build a new home, addition, or install new siding or roofing.
>You pay high energy bills. You can reduce energy cost by as much 33%.
>You are bothered by noise from outside. Insulation muffles sound.
If you have less than R-30 in your attic (11 inches of fiber glass or rock wool or 8 inches of cellulose), you will benefit by adding more. In the Chicago area you should have between R-49 and R-60 insulation in the attic (18 to 21 inches). Don’t forget the attic trap or access door.
Hope this helps