##ABOUT BLOWN-IN OR LOOSE-FILL INSULATION
Typical wall and ceiling cavities aren’t uniform in size; some are 22 1/2 in. wide, while others are narrow. They can include electrical boxes, wiring, plumbing vents, and blocking. Because of these variations, it’s hard to get batt insulation to conform to all the voids in a stud or joist bay.
In contrast, blown-in insulation provides better performance than batts by filling odd-shaped cavities completely.
##BLOWN-IN OR LOOSE-FILL CELLULOSE
For many green builders, cellulose is the first insulation choice for above-grade walls and ceilings. It is environmentally friendly, is inexpensive, and performs well.
Although cellulose insulation is not an air barrier, it is much more resistant to airflow than fiberglass. Cellulose insulation is blown in place, so it does a better job at filling cavities completely than fiberglass batts. For these reasons, a given thickness of cellulose almost always performs better than the same thickness of fiberglass—even though the insulating value of cellulose (R-3.1 to R-3.7 per inch) is comparable to that of fiberglass batts.
Cellulose insulation has several environmental advantages. It is made from ground-up newspaper; most brands contain 75% to 80% recycled newspaper (often post-consumer). The shredded paper is mixed with nontoxic borate or ammonium sulfate fire retardants.
When it is damp-sprayed into open cavities or blown into closed cavities at relatively high density, cellulose insulation adds to the airtightness of the house. Also, the quality of the installation is less contractor-dependent than fiberglass batts.
Cellulose can be installed in existing wall cavities through holes drilled in the wall sheathing, plaster, or drywall. One or two holes are drilled in each stud bay. A good installer should understand how to achieve a so-called “dense-packed” installation.
A new home can be insulated with cellulose using one of four techniques:
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