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Cellulose Insulation

Learn the Facts About this Common Type of Blown-In Insulation


Blown In Insulation

Blown In Insulation in Attic to a Depth of 12 Inches

Public Domain: CDC
When you install blown-in attic or wall insulation, chances are pretty good that it will be cellulose insulation.

Q: What is cellulose insulation?

A: The short answer: Paper. While cellulose insulation has been used for many years, it really wasn’t until the 1970s that cellulose insulation came into wide-spread use in the U.S. and other developed countries. Strictly speaking, cellulose insulation can come from any cellular plant source (corncobs, sisal, sawdust, etc.), but generally it is made from recycled newspapers, cardboard, office paper, and the like.

Q: Isn’t paper a bad thing to insulate with, considering the possibility of fire?

A: True, but cellulose insulation is treated with borates, which are a Class I fire retardant. Class I refers to ordinary combustibles such as wood and paper, as opposed to Class II combustibles such as flammable liquids, grease, gasoline, oil, etc.

Q: What is loose-fill cellulose insulation?

A: There are several different types of cellulose insulation, but the most common type that homeowners will encounter is called loose fill. Pellets of cellulose are blown into attics or walls (with holes drilled to permit access) and allowed to fill the cavities. No pressure is placed on the cellulose, though this is also a method of dense-packing the cellulose that will raise the R-value of the insulation.

Q: What is the R-value of cellulose insulation?

On the face of it, cellulose insulation has an R-value of about 3.5 per inch of thickness, compared to fiberglass batt’s R-value between 3 to 4 per inch. Overall, fiberglass batt more fully covers attic and wall cavities and is denser. So, fiberglass is considered to have an overall better R-value than cellulose insulation.

Q: How does cellulose insulation perform against moisture, insects, vermin, etc.?

Fiberglass is better against moisture because it does not absorb water. By contrast, cellulose soaks up moisture and takes a long time—if ever—to dry out. If you have ever owned a down coat or sleeping bag, you know the warnings against getting this insulating material wet: moisture dramatically cuts R-value. Regarding insects and vermin, cellulose insulation does well because of the treatment with borates.

Q: How “green” is cellulose insulation?

Pretty green. It uses up to 85% recycled materials, with the remaining 15% made up of the boric treatment. Fiberglass typically is made up of only 30-35% recycled materials, if even that.

Q: How can I decide whether to install cellulose insulation in my walls or attic?

With closed walls, you often have no other choice. Unless you are going through some remodeling where the walls are being opened up, you will need to blow in insulation. For attics, the joists are usually open and accessible to fiberglass batts. However, because of obstructions like wires (and just because of its sheer ease), cellulose insulation is often blown into attics, as well.
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