Attic Insulation Cellulose Over Fiberglass

You can get to the same place with either material.

Attic insulation cellulose over fiberglass.

Cellulose is recycled newsprint treated with a fire retardant. Originally posted by benjamin thompson part of the advantage of cellulose is the tight air barrier. Cellulose can slow down air flow particularly in walls. The bottom line is that cellulose can burn but fiberglass will not support combustion.

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. Neither type of insulation acts as an air barrier. Any existing batt or roll insulation in the attic should have the facing against the attic drywall floor or no facing at all. 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.

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. 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. Rather than trying to meticulously lay fiberglass insulation over the attic homeowners and builders can simply blow cellulose insulation throughout the attic. Thus creating a more energy efficient home.

When there are fiberglass batts in your attic the cellulose will not draft block the top plates. Batt or rolled insulation or blown loose fill insulation fiberglass or cellulose can be installed on top of old insulation. The vapor retarder on top of or between layers of insulation can trap moisture. 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.

This allows the insulation to get into the small pockets and crevices that fiberglass wouldn t be able to. Or 7 inches of cellulose. Also cellulose is a dusty product whereas fiberglass blows in pretty clean. To hit code minimums you ve got to add new insulation on top of the old insulation.

The trapped air molecules in the insulation are pulled up through the insulation into the colder attic air. Its installation costs are higher. 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.

I would add more fiberglass insulation to the top of what you already have as it will not compress as much as cellulose does. Fiberglass is just that thin fibers of glass that trap air. Insulation should be rolled out perpendicular to the joists and unfaced rolls should be used.