The recommended level for most attics is to insulate to R-38 to R-49 or about 10 to 16 inches, depending on insulation type.
A lack of attic insulation is one of the main sources for high utility bills.
When should I add insulation
Do I Have Enough?
No matter what kind of insulation you currently have in your attic, one quick way to determine if you need more is to look across the span of your attic. If your insulation is just level with or below your attic trusses you should add more. It is important that the insulation be evenly distributed with no low spots; sometimes there is enough insulation in the middle of the attic and very little along the eaves.
How Much Should I Add?
Insulation levels are specified by R-Value. R-Value is a measure of insulation's ability to resist heat flow. The higher the R-Value, the better the thermal performance of the insulation. The recommended level for most attics is to insulate to R-38 to R-49 or about 10 to 16 inches, depending on insulation type.
Add the Right Kind of Insulation
When adding additional insulation, you do not have to use the same type of insulation that currently exists in your attic. You can add loose fill on top of fiberglass batts or blankets, and vice-versa.