Whether referred to as self-supported, wet-spray, damp-spray stabilized, spray-on, or dimensionally stable, sprayed-in-place insulations are basically modified loose-fill products that are blown into wall cavities or attics. Cellulose, fiberglass, and rock wool are the most common materials used today. This method is similar to the exposed sprayed fireproofing systems commonly found on structural members in many commercial buildings. In contrast to the materials discussed in Chap. 7, a special blowing machine that combines an adhesive, water, and the insulating materials sprays the mixture into or over open wall and ceiling cavities. Sprayed-in-place insulation systems are especially advantageous when insulating irregular or out-of-square framed structures as well as walls with unusual interior geometry (such as cross-bracing, blocking).
Sprayed-in-place insulation adheres tightly to walls, framing members, and any other construction materials it may come into contact with. When installed properly, sprayed-in-place insulation uniformly covers the applied area, completely surrounding any obstructions within the cavity. The adhesive binds the insulation material to itself and to the application area. The adhesive is either a liquid that mixes with the insulation at the nozzle of the blowing machine or a powder premixed in the insulation material.
When applied correctly, this insulation resists settling and shifting and allows the cavity to be filled completely. By forming a continuously uniform blanket throughout the wall cavity, sprayed-in-place insulation allows no air gaps and provides very
good resistance to air leakage while not creating any inherent resistance to moisture transmission.
Sprayed-in-place insulation is most practical for new construction or unfinished spaces such as basements with exposed studs. Installing sprayed-in-place insulation is often messy, since some of the insulation can become airborne or adhere to the stud faces and floor. After spraying, the stud faces are scraped clean to provide a flush blanket in the wall cavity. The excess insulation is recycled into the blowing machine for reuse as long as it is free of debris.
Sprayed-in-place insulation in unfinished spaces needs time to dry before being enclosed or sheathed. Sealing up the wall too soon after application sometimes leads to moisture problems, such as mold and mildew growth. 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 the climate. Most products in use today require no more than 24 hours for drying.
There are a few general limitations. For example, the chemical fire retardants in some products may corrode the metal fasteners, piping, conduit, or structural members they contact. The long-term stability of some plastics in contact with such chemicals is also of concern.
R-value is important, but it is only one of the many factors that affect the actual performance of insulation as installed. Other important factors to consider include air permeability, ability of the insulation to “tighten” the building against air infiltration, susceptibility to convective heat loss under cold conditions, the potential for moisture permeation and accumulation and its deteriorating effects, and proper installation.
Sprayed-in-place insulation of any form should not be relied on to prevent moisture movement within an insulated cavity. Whether blown-in fiberglass, rock wool, slag wool, or cellulose is used, vapor retarders are required unless proper ventilation is provided. As with fiberglass batt insulation, materials used for vapor retarders for blown-in insulations must have a permanence rating of less than 1 perm. In a ceiling where the space above is adequately ventilated, a vapor retarder may not be required. The exception would be in cases where the cold side cannot be ventilated.1
Generally speaking, sprayed-in-place insulation systems (including installation costs) are usually more expensive than blanket insulation products. When comparing “apples with apples,” sprayed-in-place fiberglass or cellulose insulation costs are comparable. Wet-spray rock wool and slag wool are often less expensive where available. Prices vary, however, depending on local supply and on labor rates.2
A similar system, proprietarily known as the Blow-In-Blanket System (BIBS), uses a form of wet – or dry-applied wall insulation. Fiberglass material is blown into the netted wall cavity either dry or with an adhesive binder.