Blown insulation is popular for tight corners and attics.
Blown-in fiberglass and rock wool insulation are used in situations when you need a material that conforms to the existing space without having to move or alter structures or finishes. For this reason, blown insulation is often chosen to retrofit or replace old insulation that's disintegrating and in spaces that are hard to reach. Fiberglass and rock wool are among the most popular choices for blown-in insulation.
Fiberglass
Most manufacturers use 20 percent to 30 percent recycled glass to make blown-in fiberglass, according to the U.S. Department of Energy. The pink, blanketlike roll-on fiberglass insulation is the most common type of insulation used in residences in the United States, while the blow-in form is used more selectively and less frequently. Like blown-in rock wool, fiberglass is not an easy do-it-yourself project, as you need to know use the blow-in equipment and accurately determine the right thickness of insulation to use for various surfaces.
Rock Wool
Loose, blown-in rock wool is made of about 75 percent recycled steel slag and 25 percent basalt rock. It is not as popular in the United States but is widely used in Canada, Europe, Australia and New Zealand. Rock wool is known for having insulation properties and performance similar to those of wet-blown cellulose. This makes it a popular choice for sealing wall cavities. Rock wool is the only type of insulation that will stop fire.
Similarities
In addition to the blown-in format, fiberglass and rock wool are available in batts for roll-on applications. Both are also referred to as "loose-fill" insulation. Some installers may recommend using a combination, with blown-in insulation for crevices and hard-to-reach areas, and roll-on insulation on walls or floors to complete the insulation project. Installers use a technique called "open blow" with both fiberglass and rock wool insulation.
Differences
All insulation has an R-value, which relates to its thickness on a per-inch basis. Blown-in fiberglass has an R-value range of 2.20 to 4.30, and rock wool has an R-value of 3.10 to 4.00, according to Colorado Energy.org. The R-value is used to determine how much insulation is needed for various surfaces. For example, an attic floor covered with plywood might require an R-value of 30. By dividing the R-values for fiberglass and rock wool, you determine how much insulation you need. In this example, you need to blow in around 7 to 13 ½ inches of fiberglass and between 7 ½ to 9 ½ inches of rock wool.
Considerations
One thing you have to watch out for with blown-in insulation is fluffing. This occurs when insulation is skimped on in an effort to save money and it's applied at the wrong weight and thickness. Fluffing is a natural occurrence, where the insulation fibers and materials flatten over time, similar to how a pillow deflates as it gets older. When fluffing starts, the fiberglass or rock wool insulation settles, reducing the R-value and the efficiency and effectiveness of the insulation.This is why it is important to use the right R-value and apply the appropriate amount of insulation. Fiberglass is known to be more prone to fluff than rock wool. No matter which type you use, if fluffing occurs, you will see your utility bills slowly but steadily rise in costs.
