Attic Insulation

The attic is the most important room to insulate. Make the job easier with this simple calculator.


Step 1: Find the "R" Value of your existing insulation

Type of insulation (choose one)
Fiberglass blankets or batts
Rock wool blankets or batts
Loose cellulose fiber
Loose fiberglass
Loose rock wool
Thickness of existing insulation, in inches
"R" Value of your insulation
 
Step 2: Determine how much more insulation you need
 Zone in which you live
(Choose one)
Zone 1 or 2 (R-30 insulation recommended)
Zone 3 (R-38 insulation recommended)
Zone 4 or 5 (R-49 insulation recommended)
"R" Value of your existing insulation (from step 1)
Recommended thickness of fiberglass blankets or batts:
Recommended thickness of loose cellulose fiber (blown-in insulation):

Please note: For your convenience, this calculation has been rounded up slightly.

Important reminder: Every effort has been made to ensure the accuracy of this calculation. But before purchasing materials for any project, please check amounts with your suppliers or contractors.

The attic is the easiest place to install insulation, and it is also the most important, since heat rises. However, attic insulation cannot compensate for poorly insulated walls or drafty windows and doors. Caulk any open spaces around windows and doors, and install weatherstripping wherever you feel a draft on a windy day. If your house is still a drafty heat-waster, call in an insulation pro for evaluation.

The higher an insulation's "R" value, the greater its ability to impede the flow of heat. In an attic, most types of insulation have "R" values that range from 2 to 3.3 per inch of thickness. Fiberglass and older "rock wool" insulation comes in blankets or batts (short blankets). Loose-fill (or blown-in) insulation is most often composed of cellulose fiber, but may be made of fiberglass or rock wool.

If you find loose, gray-colored insulation in your attic and your home was built between 1930 and 1970, it may contain asbestos; consult a pro to determine if the insulation poses a danger to your family.

A few tips: If the spaces between the joists are already filled to the top with loose or fiberglass insulation and you need to add more, consider two options: build up the width of the joists by nailing 2x2 or 2x4 cleats on top of them, and then install insulation between the cleats; Or, simply roll insulation over the joists. If you choose the second method, you will not be able to lay plywood or boards over the insulation to use the attic for storage space.

When installing insulation, be sure not to cover any eave vents. If an attic cannot breath, insulation can be dampened by condensation, causing it to compress and lose its insulating value.

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