Attic Insulation Cellulose Over Fiberglass

To hit code minimums you ve got to add new insulation on top of the old insulation.

Attic insulation cellulose over fiberglass. Cellulose can slow down air flow particularly in walls. 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. Cellulose is recycled newsprint treated with a fire retardant. Also cellulose is a dusty product whereas fiberglass blows in pretty clean.

Air circulates through the insulation and in the case of fiberglass this is actually part of its insulating properties. Insulation should be rolled out perpendicular to the joists and unfaced rolls should be used. When there are fiberglass batts in your attic the cellulose will not draft block the top plates. The air trapped in the pockets of the insulation is part of what insulates your home.

The vapor retarder on top of or between layers of insulation can trap moisture. 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. Fiberglass is just that thin fibers of glass that trap air. You can get to the same place with either material.

Rather than trying to meticulously lay fiberglass insulation over the attic homeowners and builders can simply blow cellulose insulation throughout the attic. Its installation costs are higher. Any existing batt or roll insulation in the attic should have the facing against the attic drywall floor or no facing at all. Or 7 inches of cellulose.

This problem has been successfully solved by installing fiberglass batt insulation over the top of loose fill or blown insulation. Thus creating a more energy efficient home. This allows the insulation to get into the small pockets and crevices that fiberglass wouldn t be able to. 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.

Originally posted by benjamin thompson part of the advantage of cellulose is the tight air barrier. Neither type of insulation acts as an air barrier. I would add more fiberglass insulation to the top of what you already have as it will not compress as much as cellulose does. The trapped air molecules in the insulation are pulled up through the insulation into the colder attic air.

Batt or rolled insulation or blown loose fill insulation fiberglass or cellulose can be installed on top of old insulation. It is sometimes treated with an acrylic binder that prevents r value degeneration over time. The bottom line is that cellulose can burn but fiberglass will not support combustion.