For most of us the attic is the most used unregulated area in our homes. It becomes a place to store memories and junk and, for some, a nice hideaway for some peace and quiet. However, since it’s also the highest point in the house, and as hot air rises, the attic is a natural path for heat loss to occur. To prevent heat loss the attic space should be well insulated. But how much insulation is enough for the attic?
The short answer is as much as you can get and a good rule of thumb is to have a R-value of 38 in your attic.
Learn More About Insulation R-Values
However, the real answer is a bit more complex. There are two factors to consider when planning to insulate your attic:
- Where do you live?
- What form of heating system do you have?
The latter question has less bearing on how much insulation you need but is still important to consider. Oak Ridge National Laboratory in Tennessee conducted a study to determine the effects that different heating sources had on the insulative properties within a house. In their study they compared six different types of heating sources: natural gas, oil furnace, electric furnace, electric baseboard, heat pump and LPG furnace. Their findings were fairly universal regardless of the location of the home. Homes with heat pumps required less insulation (although it may be better stated as retained more heat) than the other varieties followed by natural gas. The remaining sources of heat all required similar amounts of insulation to be as efficient. For example, a home in Chicago with a heat pump may only need insulation equating to an R-value of 38, while a similar home in Chicago with electric baseboard will need insulation equating to an R-value of 49.
Where you live carries a much greater weight than the heat source you have. The EnergyStar program has divided the US into 8 zones, ranging from Miami, FL (Zone 1) to Nome, AK (Zone 8).
The zone you live in will determine how much insulation you need in your attic. This range varies from a low of 30 for homes with heat pumps or natural gas furnaces in Zone 3 (i.e. most of GA, AL, AR, SC, OK, etc.) to a high of 49 for Zones 6-8 (i.e. WY, MT, NH, ME, WI, etc.)
Once you've determined the R-value of insulation you need to decide which type of insulation you will use. Depending on type, you will need somewhere between 10 and 18 inches of insulation to meet the recommended insulation values.