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.
Cellulose or fiberglass attic insulation.
Cellulose is more difficult to cheat than fiberglass.
Cellulose wins last update.
If fiberglass batts become compressed losing some of their air pockets then this insulation may be more affected by air flow than cellulose which performs well regardless of density.
Both cellulose and fiberglass insulation have their pros and cons but i feel that cellulose is the better bet overall.
When used in an attic space however both types of insulation are ineffective at air flow across the attic floor such as a strong gust of wind.
When you install insulation in an existing closed wall or in an attic it likely will be a loose fill product called blow in cellulose insulation with an attic this type of insulation is just one option along with the other popular alternatives fiberglass batts or blown in fiberglass.
Cellulose insulates better than fiberglass especially in very cold weather.
Cellulose forms a dense continuous mat of insulation in your attic.
You can get to the same place with either material.
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.
This keeps the air from moving within the insulation and from penetrations between the air conditioned space and the attic.