Attic Insulation Cellulose Over Fiberglass

Also cellulose is a dusty product whereas fiberglass blows in pretty clean.

Attic insulation cellulose over fiberglass.

The trapped air molecules in the insulation are pulled up through the insulation into the colder attic air. Its installation costs are higher. Rather than trying to meticulously lay fiberglass insulation over the attic homeowners and builders can simply blow cellulose insulation throughout the attic. Cellulose is recycled newsprint treated with a fire retardant.

Fiberglass is just that thin fibers of glass that trap air. But if you have clumpy fiberglass insulation in your attic now you may want to check it with a moisture meter before adding anything on top of it. One of the benefits of placing cellulose insulation over fiberglass insulation is the cellulose if installed properly will provide an air barrier something fiberglass insulation cannot do. The vapor retarder on top of or between layers of insulation can trap moisture.

Most attics are insulated with blown in loose cellulose r 3 5 per inch blown in loose fiberglass r 2 5 per inch or fiberglass batts r 3 2 per inch. When there are fiberglass batts in your attic the cellulose will not draft block the top plates. It will however fill in all the gaps that fiberglass batts leave along side of your ceiling joists if you see wood its no good and add the to your r factor cellulose is second best with spray 2 part high density spray foam as first in my book. Neither type of insulation acts as an air barrier.

Originally posted by benjamin thompson part of the advantage of cellulose is the tight air barrier. This allows the insulation to get into the small pockets and crevices that fiberglass wouldn t be able to. Any existing batt or roll insulation in the attic should have the facing against the attic drywall floor or no facing at all. Assuming your current attic insulation is made from fiberglass and has a value of r 13 you d have to add roughly 10 inches of additional fiberglass to hit r 38.

It is sometimes treated with an acrylic binder that prevents r value degeneration over time. Or 7 inches of cellulose. It has a higher r value per inch in comparison to it close competitor fibreglass r 3 2 r 2 2 per inch cellulose is less of a health risk compared to fibreglass. Air circulates through the insulation and in the case of fiberglass this is actually part of its insulating properties.

The air trapped in the pockets of the insulation is part of what insulates your home. Insulation should be rolled out perpendicular to the joists and unfaced rolls should be used. This problem has been successfully solved by installing fiberglass batt insulation over the top of loose fill or blown insulation. You can get to the same place with either material.

The bottom line is that cellulose can burn but fiberglass will not support combustion. I would add more fiberglass insulation to the top of what you already have as it will not compress as much as cellulose does. Thus creating a more energy efficient home.