Fiberglass Attic Insulation R Value

Insulation level are specified by r value.

Fiberglass attic insulation r value.

The higher the r value the better the thermal performance of the insulation. R value is a measure of insulation s ability to resist heat traveling through it. The table below shows what levels of insulation are cost effective for different climates and. R value is a measurement of thermal resistance and measures the ability of heat to transfer from one side of an object to another.

Achieving greater r values in exterior walls. If the attic is already insulated you ll want to check the current r value. This calculator is to be used as an estimating tool only. As you can see there s some variation in r value depending on the particular type and brand of products used.

Houses in a cold climate should have a minimum of r 49 in the attic which is equivalent to approximately 16 of fiberglass insulation. The loss of r value started at a temperature difference of about 32 f. You can achieve better thermal performance in your attic by adding an additional layer of insulation. It can be located on a card left by the previous installer printed on the attic insulation or you can measure it yourself.

The loose fill fiberglass showed a significant reduction in r value as the attic got colder and the temperature difference got larger. As a benchmark one inch of solid wood has an r value of 1. Input depth of existing blown in insulation in inches. 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.

Warmer climates only require an r 38 or higher or about 12 or more. 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. First you ll need to determine your r value. If it s a new building simply reference the energy code map.

The higher the r value the better the thermal performance of the insulation.