So, You Want to Insulate Your Home: Choosing the best Insulation Material (Part 3)
Cellulose insulation is primarily made of recycled materials such as newspaper. While its structure allows it to block airflow better than fiberglass insulation, cellulose still allows some air to pass through it. This is why it is recommended to air seal before the installation of cellulose. Some brands of cellulose contain borate, an additive that helps deter pests from nesting, helps to prevent mold and mildew, and in case of fire causes the insulation to char instead of catch fire. Cellulose can be used in various applications and is commonly installed in attics, walls, and garage ceilings, it is NOT recommended for use in the crawl space.
When installed in the attic, cellulose insulation can be used in two different applications, dense pack and blown in. Dense pack cellulose is used to insulate from the attic rafters. Proper vents are installed and a netting is put up that holds the insulation in place. Holes are cut in the netting so a hose can be inserted and the cellulose can be packed into the cavity. This is a good option for homeowners who are planning to finish their attic or who have HVAC equipment/ductwork in their attic. Blown in insulation is used to insulate from the attic floor. Once the old insulation is removed and air sealing is completed, new cellulose insulation is blown into the specified R-value. If your home has recessed can lights in the attic, it is advised that you install recessed can light covers before covering these lights with insulation. Not only is this a factor in effectively air sealing your attic, but insulation in direct contact with a recessed can light can pose a fire risk as can lights can get extremely hot.
Cellulose can also be used to insulate wall cavities in both new construction and retrofit (existing homes) applications. In a new construction setting, insulation is installed before drywall which allows the installer to fill the wall cavity using a spray application. This allows the insulation to stick to the wall and itself until the cavity is filled. The excess is removed so that the insulation is flush with the studs and the drywall is ready to be installed. In a retrofit application, holes can be cut from either the inside or outside of your home (this generally depends on the exterior of the home) and insulation can be packed in using a hose.
In many cases, homeowners with a room over the garage tend to notice that this room is hotter or colder than the rest of the house. This is often due to a lack of insulation between the garage and the room above it. In this instance, an access would be made and cellulose insulation would be packed into the cavity, similar to filling a wall or an attic rafter.