Fiberglass Attic Insulation R Value

In comparison an inch of blown fiberglass insulation has an r value of 3 1 3 4 and an inch of blown cellulose in an attic has an r value of 3 2 3 7.

Fiberglass attic insulation r value.

The higher the r value the better the thermal performance of the insulation. First you ll need to determine your r value. The loose fill fiberglass showed a significant reduction in r value as the attic got colder and the temperature difference got larger. It can be located on a card left by the previous installer printed on the attic insulation or you can measure it yourself.

Houses in a cold climate should have a minimum of r 49 in the attic which is equivalent to approximately 16 of fiberglass insulation. If the attic is already insulated you ll want to check the current r value. Depending on where you live it s recommended that attics have a minimum r value of r 30 in warm climates to r 60 in cold climates. You can achieve better thermal performance in your attic by adding an additional layer of insulation.

If it s a new building simply reference the energy code map. The loss of r value started at a temperature difference of about 32 f. As you can see there s some variation in r value depending on the particular type and brand of products used. R value is a measurement of thermal resistance and measures the ability of heat to transfer from one side of an object to another.

Insulation level are specified by r value. In fact the loose fill fiberglass lost 35 to 50 of its resistance to heat flow at temperature differences of 70 f to 76 f. Recommended home insulation r values. Achieving greater r values in exterior walls.

Click the button to calculate the approximate r value for this job. The higher the r value the better the thermal performance of the insulation. Warmer climates only require an r 38 or higher or about 12 or more. The table below shows what levels of insulation are cost effective for different climates and.

This calculator is to be used as an estimating tool only.