There are three primary types of Loose-Fill Insulation widely used in construction; Cellulose, Fiberglass, and Rock Wool. Loose-fill-Insulation shapes itself into the spaces in which it is blown-in with special equipment and is sold in bags of shreds, granules, and/or nodules. All three types of insulation have environmental benefits as each utilizes a different ratio of recycled content. Loose-fill insulation is geared towards areas with hard to reach places and is most commonly installed in wall cavities and attics. They are especially popular for retrofit situation as they typically cause minimal disturbance to finishes. Cellulose has the highest R-Value per inch (fiberglass the lowest), Rock-Wool has the highest density/weight (fiberglass the lowest),  Below are the 3 primary types of loose-blown insulation, their characteristics, advantages, and disadvantages:
Cellulose Loose-Fill Insulation
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Has an R-Value per inch of 3.2 – 3.8. Produced from waste paper material (newspaper, boxes, etc). Chemicals are added (often Borate) to provide fire and insect resistance. Cellulose insulation’s weight make it too heavy for most 1/2″ drywall products installed on 24″ stud spacing, however 1/2″thick on 16″ centers, or 5/8″ on 24″ centers is usually acceptable to limit sag potential. Most 1/2″ drywall manufacturers recommend a maximum load of 1.3 lbs/sf on ceilings with joists spaced 24″ on center, 2.2lbs/sf for 16″ on center with 5/8″ drywall. Cellulose is often placed approximately +/- 20% heavy due to it susceptibility to settling. A typical density rule of thumb for filling walls is 3-4 lbs/cf. Unlike Rock Wool or Fiberglass, cellulose is not fire resistant and must have chemicals added to achieve the fire resistance. Water vapor from inside or outside of homes can migrate to the insulation cavities and if it reaches the dew point, can turn to liquid and saturate the insulation. Cellulose can absorb up to 20% of it’s weight in moisture.
Fiberglass Loose-Fill Insulation
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Has an R-Value per inch of 2.2 – 2.7. Produced from molten glass spun fibers. Often contains 20-30% recycled glass content. Fiberglass insulation’s lower relative density/weight makes it suitable for 1/2″ thick drywall on 24″ spacing, 1/2″ thick on 16″ centers, or 5/8″ on 24″ centers to limit sag potential. Most 1/2″ drywall manufacturers recommend a maximum load of 1.3 lbs/sf on ceilings with joists spaced 24″ on center, 2.2lbs/sf for 16″ on center with 5/8″ drywall. Fiberglass insulation is more susceptible to air flow because it is less dense. A typical density rule of thumb for filling walls is 1-2 lbs/cf. Fiberglass is naturally fire-resistant. Water vapor from inside or outside of homes can migrate to the insulation cavities and if it reaches the dew point, can turn to liquid and saturate the insulation. Fiberglass only absorbs up to 1-2% of it’s weight in moisture.
Rock Wool Loose-Fill Insulation
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Has an R-Value per inch of 3.0 – 3.3. Produced from glass-furnace slag spun fibers (byproduct that forms on the surface of molten metal). Other rock materials are also added. Rock Wool insulation’s weight make it too heavy for most 1/2″ drywall products installed on 24″ stud spacing, however 1/2″thick on 16″ centers, or 5/8″ on 24″ centers is usually acceptable to limit sag potential. Most 1/2″ drywall manufacturers recommend a maximum load of 1.3 lbs/sf on ceilings with joists spaced 24″ on center, 2.2lbs/sf for 16″ on center with 5/8″ drywall. A typical density rule of thumb for filling walls is 1-2 lbs/cf. Rock Wool is naturally fire-resistant. Water vapor from inside or outside of homes can migrate to the insulation cavities and if it reaches the dew point, can turn to liquid and saturate the insulation. Rock Wool only absorbs up to 1-2% of it’s weight in moisture.
Installation of loose-fill insulation in a wall cavity is commonly done by drilling +/- 2″ holes into each stud cavity.
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Also an approach called the ‘two-hole method’ may be used which requires drilling a hole at the top (+/- 16″ down) and the bottom (24″ up) of the wall. However, each installer is different in his or her approach to installation.  Afterwards the holes are patched to match the existing finish. Installation of loose-fill insulation in ceilings is much easier from an access standpoint as all areas can be relatively easily accessed. Voids and gaps should be avoided. Also an action called ‘fluffing’ should be avoided as well which includes installation to minimum thickness but not weight requirements. Fiberglasss ‘less-dense’ composition tends to be more susceptible to this issue. In attics the top plate of the wall should be covered but not the eave venting system. Typically at least 3″ of clearance is needed from all electrical lighting and boxes. Some contention has emerged on the carcinogenic nature fiberglass particles, fire-retardants, and insecticides used in many loose-fill insulations so proper personal protective equipment (PPE) should be worn, i.e. eyewear, respirater, long-sleeve shirts, gloves, pants, etc.
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Also duct work access should be blocked off before insulation to avoid circulation into the system. For ceiling applications, it’s common for thickness gauges or marker to be installed on the joists for every +/- 300sf of attic space showing the thickness and/or R-value of the insulation per building code and/or inspection.
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Also some jurisdictions require that a permanent inspection certificate be obtained and installed on the electrical panel showing adherance to the required R-Values at time of installation.
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While not commonly required by building codes, insulation installation may be done by a certified installer experienced in operating the equipment and ensuring correct density, thickness, and coverage.
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