Consider cost in determining most effective level of insulation

Editor's note: The Energy Services Bulletin features real answers to real questions posed to our staff at the Energy Services Power Line. We hope you find it useful.

How much insulation can be installed in a roof before the weight of the insulation causes it to compress to the point where it is less effective?

We posed your question to industry expert Daniel Lea at the Cellulose Insulation Manufacturers Association. Here is his response:

Compression of the insulation is not the issue. Adding more insulation in an attic environment will always increase its installed R-Value. The question is at what point does the cost (financial and invested energy) of the additional insulation enter the negative return range. Based on an analysis by Oak Ridge National Laboratory, the Department of Energy determined that, in most of the United States, that point is R-49. In near arctic climates, DOE ups this to R-60.

It is important to note that the point of diminishing returns will vary by the cost of the insulation product, the cost of fuel to heat or cool the building, and the temperature range of the environment (both indoor and out).

• Standard Practice for InstallingCelluloseBuilding Insulation (56K Adobe® Acrobat® .pdf): CIMA Technical Bulletin.
• "Insulation"; DOE Building Technologies Program.
  Basic information about insulation.
• DOE: A Consumer's Guide to Energy Efficiency and Renewable Energy
• "Estimating the Payback Period of Additional Insulation": This webpage provides an equation to estimate the cost effectiveness of adding insulation in terms of the "years to payback" for savings in heating costs.
• "Loose Fill Insulation":  This covers different types of loose fill insulation, recommended specifications and installation tips.
• "The R-Value of Insulation": This contains general information on insulation R-values.