How Long Does It Take for Blown-In Insulation to Settle?

About Blown-In Insulation

• Blown-in insulation, also called loose-fill insulation, uses small pieces of material to fill attic and wall spaces. Using these materials provides the barrier to keep hot air in during the winter, as well as keep air-conditioned air in during the hot months. The advantage of blown-in insulation is that the loose pieces easily fill in areas around electrical equipment and ductwork, creating a continuous layer of insulation with the least amount of labor. It is best done by an insulation contractor who can install the materials without gaps or voids.

Fiberglass Insulation

• Blown-in insulation is available in several different materials. Fiberglass is a common form that is used in homes. To make fiberglass, molten glass is shot through tiny holes in a high-speed stream to create a fine material that is enclosed in membranes to prevent tiny shards of glass from floating in the air. It is loose and may settle slightly over weeks or months, though less than other types of blown-in insulation.

Cellulose Insulation

• Cellulose material that is blown into cavities of a home is made from small bits of recycled newsprint or cardboard treated with fire retardant. It is sometimes enclosed in a netting or membrane to keep it in position. Cellulose settles more than other blown-in materials. It can settle as much as 20 percent over the first few years after installation, according to writer Benjamin Hardy of the BobVila website.

Rockwool Insulation

• Rockwool is yet another type of material used for blown-in insulation. It is made from recycled steel slag and natural rock such as limestone, basalt or diabase. It is blown into wall cavities as well as unenclosed spaces. Rockwool retains its R-value, the measure of resistance to heat transfer, because it resists settling, according to the LinyinInsulationMaterials website. It is four times as dense as fiberglass and is naturally resistant to fire. Though more expensive than other types of insulation, rockwool offers many advantages, including acoustical properties, that make it a desirable product for consumers.

How Long Settling Can Occur

• Blown-in insulation can continue to settle for weeks, months and even years. The best way to determine how much settling is actually happening is to install attic insulation rules at several points along the eaves, marking the initial depth of the insulation at installation. Periodically check the ruler to determine how much the material has settled. Because the settling decreases the R-value of the material, you may need to consult with your insulation contractor to install additional insulation.