Because it is denser than fiberglass cellulose is much more resistant to wind washing.
Fiberglass insulation vs cellulose insulation for attic.
Cellulose provides better sound insulation than fiberglass i e homes are less noisy with it.
You can get to the same place with either material.
Or 7 inches of cellulose.
Rather than trying to meticulously lay fiberglass insulation over the attic homeowners and builders can simply blow cellulose insulation throughout the attic.
Cellulose insulation is considered green as it is made from recycled newspaper and requires less energy to manufacture than fiberglass insulation.
This is called wind washing.
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.
Dirty fiberglass batts have a significantly reduced r value.
The two main least expensive and most commonly used residential insulation materials is cellulose and fibreglass.
Air moving through a vented attic deposits dirt and dust into fiberglass batts.
Unless you opt for spray foam then the insulation choices normally come down to cellulose and fibreglass.
Fiberglass is a suspected carcinogen.
Many fiberglass installers fluff the fiber with extra air so you don t get as much insulation as you re supposed to.
It has a better resistance to air flow and prevents the upward movement of air caused by temperature differences.