Interior Heating & Cooling Insulation

Blown-In Insulation vs. Spray-In Foam Insulation

There are different methods for spraying different kinds of blown insulation into the walls, attics, and floors of your home.
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Worker sprays blown in fiberglass insulation in attic.
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Blown-In Insulation

Blown-in insulation products are competing to bring improved performance per square inch and the least amount of settling over time to the insulation market. Blown-in insulation refers to blowing or spraying insulation product into wall cavities, attics, and floors. Methods vary depending on the form of insulation selected.

Loose-Fill Fiberglass
In its loose-fill form, fiberglass is made from glass that is blown or spun into fibers. It is installed using a blowing machine. Loose-fill fiberglass is suitable for attics and wall cavities and can combat common insulation enemies like mildew, fungus, and moisture. “Our OPTIMA insulation is made of virgin fiberglass,” says a CertainTeed representative, “so it won’t rot or absorb moisture.” Critics do contend that many fiberglass products include recycled glass and that loose-fill fiberglass can leave floating particles in the home.

Blow-in cellulose insulation has been around since the 1920s and consists predominantly of recovered or recycled newsprint and/or corrugated cardboard, treated with a fire retardant. Three main types of blow-in cellulose insulation are used in residential application: loose fill, stabilized, and wall-cavity spray.

Spray-In Foam Insulation

Spray-in or spray-on polyurethane foam expands to fill cracks and voids to form a tightly sealed barrier. Foam’s biggest advantage is it virtually eliminates air infiltration. In most cases the foam is mixed on site, where trained professionals do the installation. “The spray-on foam is a pretty popular option,” says Michael Kwart, executive director of the Insulation Contractors Association of America, “but it requires higher skill training.” Spray foam is used in attics, ceilings, walls, and floors. When applied, it expands to 100 times its volume to seal cracks and crevices. It also maintains some flexibility as the home ages.

Depending on the product used, foam can provide the highest R-value per inch of the three forms of insulation discussed at 3.6 per inch. “We use an expanding foam in closed-cell application that has an R-value of 6.5 per inch,” says Joe Ann Hurst, president of Astro Insulation in Chicago. “It is a very effective air barrier.” It is also fairly expensive. Depending on the region and market, spray-foam insulation can sell for $1.30 to $3.50 per square foot. In most home markets, this type of insulation is considered an added home value that will pay back over time and in the sale of the home.

Greener Insulation Options

Homeowners looking for a natural alternative to chemical foam insulation might look at soy. With none of the CFC’s, HCFC’s, or Formaldehyde that spark concern among indoor-air-quality experts, green builders and consumers are turning to soy-based foam. This spray foam is made from soy beans or castor beans and polyurethane foam. Like its chemical cousin, soy-based foam forms a total air barrier by filling voids and crevices to prevent air intrusion. It is inert, will not support moisture or mold, and is durable. Advocates point to the sustainability of an industry that encourages planting, harvesting, and manufacture of a product that will in turn save energy.

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Loose-fill cellulose blow in insulation is a dry install for walls and attics. Run through a blowing machine, loose fill can be installed in a wall through access holes after the interior finish has gone up, or installed into a netting system or reinforced poly-barrier retaining membrane. Loose-fill cellulose should never be blown into exhaust fans or come into contact with any overhead lighting or lighting fixtures.

Stabilized cellulose contains a slight moisture additive and adhesive, so it is useful in horizontal applications such as attics. Builders and installers often choose to use stabilized cellulose because the moisture controls the dust, and the product is less expensive. “The density of stabilized cellulose is such that a builder doesn’t have to use as much to achieve the R-value. To a builder putting up a large number of homes, this means savings,” says Daniel Lea, executive director of the Cellulose Insulation Manufacturers Association.

Wall-cavity spray is used in vertical installs and includes a moisture additive, typically up to 10 percent, which allows it to adhere to vertical surfaces. It is important that the wall cavities not be closed before the insulation has dried completely. “Some folks are set against adding moisture to the walls,” says Lea, because it can encourage mildew or fungal growth. Wall cavity spray eliminates the worry of settling and is also considered the cheapest to install, as it is less labor intensive and requires no retaining membranes.

Cellulose can provide excellent sound attenuation properties, and is very competitive in price. Depending on the region, market, and the specific product used, cellulose can cost under $1.00 per square foot. “Our cellulose insulation runs about 84 cents per square foot,” says Harrah. “If I had a choice between fiberglass, foam, and cellulose, I would go with cellulose.” A wet-spray cellulose install can provide an R-value of around 3.4 per inch.

Combatting Settling

Settling occurs over time and can compromise a home’s insulation. Loose insulation has been found to settle as much as 20 percent over the first few years after installation, so it’s important to have a gauge and guarantee from the installer. Each installer should provide an attic card affixed to the roof truss as a standing measure that states the type of insulation, density, amount installed, and installer’s contact information. Installers verify density by following the prescription for the exact number of bags needed to reach the desired R-value. The bag to density formula is printed on each bag.