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Cellulose insulation’s primary ingredient is one of the world’s largest solid waste byproducts: discarded newspapers. In fact, the finish product is 80 percent recycled newspaper by weight. Increased marketshare for cellulose insulation has the distinct advantage of creating a market and motivation for newspaper recycling programs. This is a significant market considering the fact that each year, 13 million tons of newspaper—about 100 pounds per person—are produced and discarded here in North America. Though recycled newspaper can be reincarnated into new newspapers, the process requires de-inking and bleaching which in turn generates contaminated water. A lot of energy is required to treat and decontaminate this tainted water.

On the other hand, cellulose insulation production—because of its low-tech nature—is an ideal reuse for discarded newspapers. Though ink is used in the printing process, de-inking is not required for producing cellulose insulation. Modern printing technology has for the most part substituted soy-based inks for petroleum based black inks. Color inks cause the main concern regarding the ink content in recycled newspaper. Heavy metals such as cadmium and lead were used in the production of color print when first introduced in the early ’80s. By then, the dangers posed by heavy metals to human health were well known and their use has since been banned.

Another appealing aspect of using recycled newspaper to produce cellulose insulation is the low energy or aka, EE required to produce it. Based on a 1991 study cellulose insulation, inclusive of its fire-retardant chemicals (20 percent by weight), requires only a fraction of the EE of other common insulation materials:

• Insulation material: EE (Btu per pound)

• Cellulose: 750

• Fiberglass: 12,000

• EPS: 48,000

• Isocyanurate: 30,000

Besides its low EE, the manufacturing process produces no pollution. In fact, since the process is relatively simple, production facilities can be numerous, wide spread and small in size. This keeps transportation energy low. Not including the chemical additives and transportation energy, the net energy consumption of cellulose insulation is estimated to be as low as 145 Btu per pound. By comparison, fiberglass insulation production is the very opposite. It requires large, complex production facilities few in number and remote from the marketplace. This entails high transportation energy costs to bring the finish product to the end user.

Cellulose insulation is not suited for reuse as an insulation material as the result of renovation and/or demolition. Being biodegradable, cellulose insulation is typically disposed of in landfills or incinerated at the end of its lifecycle as an insulating material. Though the cellulose content is completely biodegradable, the fire-retardant chemicals such as borate and ammonium sulfate are not. Since these chemicals are water-soluble and will produce a leachate (dissolves in rainwater), there is concern over permeation into the ground soil below the landfills where it is buried.

A legitimate concern however: Studies have shown that the toxicity levels in cellulose insulation is low enough so as not to be considered unsafe for landfills. Even the Golden State, California, with the most stringent pollution control laws in the United States, allows cellulose insulation to be buried in landfills.

Hero or zero?

Aside from its economic and environmental benefits, there are four major areas of concern regarding cellulose insulation: health, fire safety, corrosive effects and dry out.

Some Healthy House advocates suggest that the fire-retardant chemicals and the cellulose fibers themselves are harmful to human health and/or are carcinogenic (cancer causing). Much of this concern is tangential to the bitter experience of airborne asbestos fibers in building materials of years gone-by. Borates and boric acid, chemical additives to cellulose insulation, are known toxins which can be fatal to humans if ingested—so do not eat it. Toxic poisoning can occur through a cut or laceration of the skin. Symptoms of poisoning include:

• Abdominal pain

• Liver, kidney and lung dysfunction

• Severe exfoliative dermatitis

Cellulose dust can/will deliver the readily soluble boric acid it contains into lung tissue. Therefore, it is important to wear protective clothing and use an appropriate respirator, not a simple dust mask, when installing cellulose insulation. It is the installation process rather than the manufacturing or installed-in-place cellulose insulation that poses the greatest health risk to humans. The potential for cellulose insulation to “liberate respirable fibers in significant amounts” is quite low for properly installed cellulose insulation. As an added measure of protection, an air-tight barrier, either a polyethylene vapor-barrier or well-sealed gypsum board (air-tight), should be provided between the living space and installed cellulose insulation in walls and ceilings.

If I only had a brain

Like the character Scarecrow in the movie “The Wizard of Oz,” whose fear of fire was greater than his desire for being smart, cellulose, like straw, is inherently combustible and that is the primary fear factor for using cellulose insulation. It is the main reason fire-retardant chemicals are added in the manufacturing process. Of particular concern is the leaching of borates over time, thus undermining the chemical’s effectiveness for suppressing combustion.

There is ambiguous data concerning the integrity of the fire-retardant chemicals over the lifecycle of a building insulated with cellulose insulation. Some studies suggest that only at extreme temperatures and high humidity does sublimation (evaporation) of boric acid occur in any significant amount. These temperature/humidity levels are much higher than those commonly found in walls/attic spaces—even in warm climates. To corroborate the circumstantial evidence in favor of cellulose insulation maintaining its fire-retarding ability over time, statewide fire departments in California reported no incidence of insulation including cellulose as being a major fire hazard. Still, it is recommended that recessed light fixtures of any kind not be placed in close proximity to cellulose—or any type of insulation—in a clg/attic space for fear that heat generated from the light will ignite the insulation.

One of the chemicals often used in cellulose insulation is ammonium sulfate. When ammonium sulfate thermally decomposes or becomes wet it produces sulfuric acid, a corrosive to metals. For this reason, many installers will only use cellulose chemically treated with boric acid and borax not ammonium sulfate for wet-spray applications. There is anecdotal evidence of pipes and metal fasteners suffering the effects of corrosion when in contact with wet cellulose containing ammonium sulfate. Some manufacturers now add corrosion inhibitors to the chemical mix to help prevent this occurrence.

With the ongoing concern over rot, mildew and mold in buildings, there is debate over the ability of wet-spray applied cellulose insulation to dry out properly. In a worst-case scenario played out in a public housing project, 18 months after application, the moisture content in the walls was between 30 to 60 percent! Though the wall construction type (effective vapor barriers on both inner and outer sides of the wall) lent itself to magnifying the problem, it was contributory, not the culprit. Up to 200 percent moisture, on a dry-weight basis (weight of water divided by the weight of cellulose), was used for the installation. This translates to 5 to 6 gallons of water per 30-pounds bag of cellulose insulation (about 4 gallons per bag is standard). The cellulose insulation was completely over saturated with water when installed.

It appears climate too has much to do with dry-out problems with cellulose insulation. A Canadian study in the provinces of Alberta (dry climate) and Newfoundland (wet climate) had contrary results. After 120 days, the Alberta study had dried-out to acceptable levels. In the Newfoundland study, the studs in the wall contained a 60 percent moisture level after two years had passed from the time of application. Since climatic conditions are a critical factor for achieving dry-out, it is suggested that wet-spray applied cellulose be able to: dry to the exterior in northern (cold/dry) climates. This entails use of moisture permeable exterior framing and sheathing such as 1x dimensional lumber and asphalt-impregnated fiberboard. For southern (warm/wet) climates, the opposite is true. The cellulose must be allowed to: dry to the interior. The best way to do this is to eliminate a vapor barrier and install the gypsum board panels/finishes air tight.

Many installers use dehumidifiers and allow for proper dry-out to occur by leaving the wet cellulose insulation exposed for at least 48 hours. Low moisture content (50 percent maximum by dry-weight content) is also employed to minimize dry-out problems. Fiberized cellulose insulation with a binder has a moisture content as low as 28 percent (dry-weight) and is therefore favored for wet-spray applications (more about this in Part 2).