Blown insulation, also called loose fill insulation, is commonly used to insulate existing structures that previously had no insulation, or where additional insulation is needed. It is made up of loose particles which are blown into an attic or into wall cavities, which are the spaces between the interior and exterior walls of a building. Since even distribution of the material is important, and because special pneumatic equipment is required, installation is usually done by a professional.
There are three basic types of blown insulation commonly available. Fiberglass insulation consists of small particles of spun glass fibers. Mineral wool is made from particles of rock or steel slag, which is a recycled manufacturing waste. Cellulose insulation comes from recycled newspapers or cardboard which has been treated with chemicals to make it resistant to flame and insects.
In the U.S., all insulation is given an R-value, which is a measurement of thermal resistance. Insulation with a higher R-value provides more effective barriers against heat loss. R-values are based on the type of material used, as well as thickness and density of the material. The R-value for blown-in insulation depends on which type is used, as well as how much is blown in; its thickness is measured with a ruler. Blown insulation often has two R-values. The first represents its value at installation, and the second represents a lower value after the material has settled over time.
Using blown insulation has many advantages. It is fairly economical, and is much easier to install in hard-to-reach areas, as well as working around obstacles such as chimneys or stove vents. Blown-in insulation is eco-friendly because it makes use of recycled materials. It can be used as the primary type of insulation, or it can be added to other types of insulation to help fill in the gaps and provide an additional heat barrier.
Blown insulation does have some disadvantages as well. Over time, the particles settle, which reduces its R-value. Sometimes it is mixed with adhesive before being blown in; the adhesive helps the particles resist settling. There are some concerns about blown-in insulation entering the living space through gaps in the home's ductwork, and the inhalation dangers of the fine particles are unknown. With a proper professional installation, many of these concerns can be alleviated. Since blown-in insulation has a tendency to absorb moisture, a vapor barrier should be used, particularly on a new installation.
Be sure and check on your locality's building codes and regulations. In the U.S., the National Electric Code (NEC) forbids blown-in insulation in older homes with certain types of outdated wiring systems, because overheating wires can create a fire hazard. Your installation professional will be able to advise you on the best type of insulation for your particular structure. As with all insulation products, you should avoid attic vents and heat-producing obstacles such as light fixtures.