Sprayed Fiber Insulation
Cellulose, fiberglass, and Rockwool (mineral wool) insulation products are typically installed as dry, blown-in loose insulation, and in the case of fiberglass and Rockwool, as a rolls and batts. They are also available as "sprayed " products that are sprayed into place in building cavities. These used to be called "wet-sprayed insulation" because some water is generally used to activate an adhesive in the insulation so it will adhere to the building's components. The terms "sprayed" or "spray-in-place" insulation are now more widely used.
Sprayed insulation products have the advantage of completely filling voids in building cavities where rolled insulation types are difficult to cut and fit well. Since sprayed insulation tightly conforms and adheres to the building cavities, it reduces air infiltration and increases the insulation's effectiveness. It forms a uniform covering throughout the cavity and forms a good air seal between electrical wiring, pipes, framing members, and anything else inside the building cavity. Also there's little chance of the insulation settling since the insulation fibers adhere to each other and the sides of the building cavity. Poor fitting insulation yields poorer than expected insulation performance due to gaps in insulation coverage and random air movement within the insulation.
Cellulose is the most commonly sprayed insulation material used in residential buildings. A special blowing machine that combines water, an adhesive, the insulation (and a fire retardant in cellulose products) is used for applying the mixture to the building cavities. Once dry, it has an R-value of approximately 3.5 per inch of thickness, if installed at the product's recommended density. In addition to water and adhesive, a chemical fire retardant is also used in cellulose applications. The fire retardant can corrode metal fasteners, pipes, and other components that it comes in contact with.
Fiberglass is the next most commonly sprayed material for residential buildings. Sprayed fiberglass application is commonly known as the Blow-In-Blanket System (BIBS). It uses roughly the same sort of equipment and adhesive that sprayed cellulose uses. However it doesn't prevent air infiltration as well as sprayed cellulose. The dried R-value is about 3 per inch of thickness. Fiberglass requires no additional fire retardant treatments.
Rockwool insulation is most commonly used as fireproofing and thermal insulation in commercial and industrial buildings. It is seldom found in residential buildings. Rockwool yields approximately R-2.7 per inch of thickness.
There are some precautions to take when using sprayed fiber insulation. The chemical fire retardant within the products may corrode metal fasteners, pipes, or structural members that they contact. Unscrupulous installers can "fluff" blow-in-blanket insulation, installing it at lower density than disclosed to the homeowner. Excessive water content and insufficient drying may promote fungus growth inside building cavities.
Application and Cost: Sprayed insulation is most practical for new construction or unfinished spaces with exposed studs. Installations are often messy, since some of the insulation also adheres to unintended surfaces such as floors and windows. However, the adhesive binders are water-soluble so it is easily removed. After application, the stud edges are scraped clean with a special milling tool made for that purpose. As long as the "salvaged" insulation is free of debris it can be sent through the blowing machine again for reuse.
Sprayed insulation also needs time to dry before being enclosed in the building cavity. Sealing a cavity too soon sometimes leads to fungus and moisture problems. The drying time for the insulation varies depending on the type of insulation material and its moisture content, the moisture content of the framing members, and conditions such as humidity and temperature. Applications may take two days to several weeks to dry completely. Two (proprietary) techniques for faster drying times is to use Rockwool, which does not easily absorb moisture, or netting over the studs to support the insulation, with less water content, as it dries.
Sprayed insulation systems cost more than fiberglass batt insulation. However, it generally is less expensive than sprayed foam, and performs almost as well in many cases. BIBS and sprayed cellulose are often comparable in price. Sprayed Rockwool may be less expensive, however it is often difficult to find installers for residences. Prices also vary with local supply and labor rates.