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 vs fiberglass in attic.
Cellulose retains more of its r value through a wider range of temperatures compared to fiberglass.
When comparing blown in insulation both fiberglass and cellulose are nearly identical in price both costing around 0 70 to 0 80 per square foot for 6 inches of insulation.
Both fiberglass and cellulose insulation can be installed to completely fill the space inside of wall floor or ceiling cavity.
Air moving through a vented attic deposits dirt and dust into fiberglass batts.
The two main least expensive and most commonly used residential insulation materials is cellulose and fibreglass.
This is called wind washing.
Compared to fiberglass cellulose is a superb air blocker.
Higher r value per inch.
Cellulose insulation blown in wall r 3 8 r3 9.
Blown cellulose is typically the preferred choice of insulation for attics.
Fiberglass batts however are less expensive costing on average 0 30 to 0 40 a square foot for 6 inches of insulation.
Blown in cellulose homeowner benefits.
Cellulose has an r value of 3 5 3 7 per inch where fiberglass has around 2 1 2 7 r per inch.
Properly installed they will both remain in place for the life of the home.
Cellulose insulates better than fiberglass especially in very cold weather.
Rather than trying to meticulously lay fiberglass insulation over the attic homeowners and builders can simply blow cellulose insulation throughout the attic.
So it seems to me the real debate.
Unless you opt for spray foam then the insulation choices normally come down to cellulose and fibreglass.
Both cellulose and fiberglass insulation have their pros and cons but i feel that cellulose is the better bet overall.
Cellulose wins last update.
You can get to the same place with either material.
Or 7 inches of cellulose.
Cellulose insulation blown in attic r 3 6 r3 7.