Loose-fill insulation is a common solution for insulating an attic.
It will cover the surfaces well without voids or gaps, is inexpensive to
install, and is readily available. All three of the most common loose-fill
insulations are considered "environmentally positive" because they are
manufactured from recycled waste.
Cellulose is the favored type of loose-fill insulation used for the DOE-funded
low-income weatherization programs. This fire-retardant insulation is made
from recycled newspaper and boxes and does a good job of slowing airflow, even at
loose-fill densities. Additional advantages include the ability to store small
amounts of water and, because it is usually manufactured locally, it is not
shipped long distances. Cellulose has the disadvantages of braking
down when it gets saturated with water and it is relatively heavy. Because
of its weight, it is not recommended for use in mobile home ceilings or floors.
Loose-fill cellulose will settle from 10 to 20 percent over time due to gravity and vibration.
The settled density range for loose-fill cellulose
is 1.5 to 2.0 lb/ft3 (36 to 24 kg/m3) and its settled R-value per inch
is from 3.2 to 3.8 (0.222 to 0.2636 RSI per cm).
Fiberglass is lighter than cellulose and will not be permanently damaged if it is saturated
with water. It may be used in the ceilings and floors of mobile homes because
its light weight. Currently, about 20 to 40
percent of the fiberglass sold as insulation is recycled. This is a significantly
lower percentage than cellulose, but the fiberglass industry continues to make
gains. Disadvantages of fiberglass include an inability to slow airflow as well
as cellulose and rock wool and a higher cost than the other two common insulations.
Loose-fill fiberglass will settle at a rate of
from 2 to 4 percent over time. The settled density range for loose-fill fiberglass
is 0.5 to 1.0 lb/ft3 (10 to 14 kg/m3) and its settled R-value
per inch is from 2.2 to 2.7 (0.1526 to 0.1873 RSI per cm).
Rock wool is similar to fiberglass in that it is spun from molten material, but from
blast-furnace slag rather than glass. This process uses products
that would otherwise be discarded. Of the three loose-fill insulations
discussed here, it is the least common.
Rock wool will settle at a rate similar to fiberglass, from 2 to 4 percent
over time. The settled density for loose-fill rock wool
is 1.7 lb/ft3 (27 kg/m3) and its settled R-value per inch is
from 3.0 to 3.3 (0.208 to 0.229 RSI per cm).