These days most attics don't have enough insulation or have insulation that isn't working as well as it should be. An upgrade -- one that will pay off every year and in every season you live in your home -- is only one messy afternoon away. Yes, you can and should add more insulation to your attic. It's one of the best ways to increase your home's energy efficiency.
R-factor is a numerical indicator of an insulation's efficiency at retarding the flow of heat. The scale goes from low to high; higher R-numbers mean a given insulation is better able to stop heat from moving from one place to another. Current building codes recommend an insulation R-factor of R-38 for attics in most of the country. That would be about 10 to 12 inches of fiberglass batting or blown cellulose fiber insulation. Bear in mind that R-38 is actually the minimum recommended standard for attic insulation. Proposed energy codes would increase that number to R-50.
Fiberglass and cellulose fiber are the two most common attic insulation materials. Each yields an R-factor of roughly 3.5 per inch. Cellulose consists of ground-up newspaper material, which is then treated with fire-retardant chemicals. Fiberglass is made of billions of strands of extruded glass fibers packed into specifically sized batts. Some fiberglass batting now comes encased in perforated poly bags to help contain loose glass fibers and make handling and installation easier. Fiberglass also is available as a loose-fill or blown-in material.
While it is possible to do a good job fitting and installing fiberglass batting around all the many framing members and other obstructions in an attic, it is somewhat rare to see such a thorough installation. Many homeowners and insulation installers either don't understand the importance of tightly fitting the material into the many spaces that abound in an attic or find the job too tedious to do correctly. Usually there are gaps and holes between batts and between batts and framing. Those holes defeat much of the insulative value the material can provide.
Cellulose fiber, on the other hand, because it is ground into a fine material, flows and can be blown into all the attic's nooks and crannies, allowing it to do a better, more comprehensive insulation job. And nearly any determined homeowner can do it. Home centers that sell insulation of all types even loan insulation blowers to customers who buy a certain number of bags from their stores. Information on how to operate the machines and install the insulation is available in those stores and from manufacturers.
Cellulose fiber insulation is also less subject than open fiberglass to what builders call "wind wash," which is simply air currents moving through insulation, robbing it of its R-value. Fiberglass batts that are enclosed in perforated poly bags are less subject to wind wash than are either open batts or loose-fill fiberglass insulation.
Any type of attic insulation can be installed over any other type: fiberglass over cellulose, cellulose over fiberglass -- it makes no difference. The fiberglass must be unfaced, however, or encased in perforated poly bags. Otherwise, condensation could develop on the facing.
If your attic has a floor and is used for storage, the potential insulation depth is limited by the depth of the floor joists. Thus, many attics could have a substandard R-factor of only 20 or so -- unless you go to the trouble of removing the floor and adding additional framing lumber to the tops of the joists and then reinstalling the floor.
An easier solution than floor removal is to consolidate the stored items into a smaller area (or remove them from the attic entirely), and roll out poly-encased fiberglass batting on top of the floor. The batts can be removed or rolled back at any time if the space is required for storage in the future.
While the price of fuel oil, gas, and electricity continues to rise, attic insulation is relatively inexpensive and remains one of your best energy-efficiency upgrade values.
Energy efficiency isn't just about sealing and insulating your home. Dust collecting on appliances and irregular maintenance of heating and cooling equipment wastes energy. Check out how to head off these problems in the next section.