Cellulose is the oldest building insulation material. Many types of cellulose materials have been used, including newspaper, cardboard, cotton, straw, sawdust, hemp and corncob. Monticello was insulated with a form of cellulose. Modern cellulose insulation, made with recycled newspaper using grinding and dust removing machines and adding a fire retardant, began in the 1950s and came into general use in the US during the 1970s.

The market for insulation increased following the oil embargo of 1973-74. The embargo caused energy costs for heating to skyrocket across the nation, which lead to increased interest in energy conservation measures. Insulation gained significant national attention as a cheap and available technology to increase the energy efficiency of homes. In 1977, following a particularly severe winter, a tax credit was given for homeowners who installed insulation.

While in 1976 there were roughly 100 cellulose insulation firms with 125 plants, by 1978 there were more than 350 firms with more than 500 plants. Cellulose insulation was produced locally by small manufacturers who purchased ready-to-operate machines and offered a cheap and easy low-tech production process. Other than some constraints created by a shortage of boric acid for use as fire retardant, cellulose captured an increased share of the market due to lower costs and its suitability for retrofits. Meanwhile fiberglass and rock wool producers found it difficult to keep up with the demand for insulation from their customers.

Due to complaints by retailers, contractors and consumers about price, safety and quality control problems, the federal government began enacting insulation standards beginning in 1978. There was a great concern that the growth in cellulose manufactures was leading to improperly or insufficiently treating insulation against the threat of fire even though reliable statistics on a national basis did not exist. This led to the Federal Consumer Products Safety Commission passing 16 CFR Part 1209, which sets safety standards covering four product attributes for cellulose insulation only: settled density, corrosiveness, critical radiant flux and smoldering combustion. Another regulation passed was the “R-value Rule,” placing clear limitations on the claims that manufacturing and marketing firms can make about their product.

The fiberglass industry meanwhile benefited from most of the regulations passed by the federal government. The heavy lobbying by the more centralized fiberglass and mineral insulation manufacturers helped pass the tough fire standards for cellulose insulation. These standards were reinforced by technical bulletins published by the Mineral Insulation Manufacturers Association (currently known as the North American Insulation Manufacturers Association) that promoted fire hazard claims against cellulose insulation. These claims were not independently verified, faced little scientific review, and were misleading and untrue.

Currently cellulose insulation has increased again in use in the United States. Part of the reason for this growth are studies that have shown results that suggest that cellulose may actually protect a building from damage in a fire better than fiberglass because cellulose is denser than fiberglass and doesn't allow the oxygen necessary to burn structural members. Several National Research Council Canada studies have backed these claims. Another major reason for the comeback of cellulose might be because of the increased interest in green building. Cellulose has the highest recycled content of any insulation material and also has less embodied energy than fiberglass and other furnace produced mineral insulations. - Wikipedia

Advantages

• Thermal Performance
  The thermal performance of loose filled cellulose compares favorably to other types of insulation. The thermal conductivity of loose-fill cellulose is approximately 40 mW/(K*m) (an R-value of 3.8 per inch) which is about the same as or slightly better than glass wool or rock wool. This doesn’t represent the whole picture of thermal performance. Other important aspects are how well the building envelope is sealed from air infiltration, convective airflows, and thermal bridging. Cellulose is very good at fitting around items in walls like pipes and wiring leaving few air pockets that can reduce the overall efficiency of the wall. It also seals walls from air infiltration while providing the density to limit convection. The University of Colorado School of Architecture and Planning did a study that compared two seemingly identical test structures, one with cellulose and the other with fiberglass. The cellulose structure had used 26.4% less energy to heat. It also was shown to tighten the structure more than 30%. Subsequent real world surveys have cellulose performing 20-30% better at reducing energy used for heating than fiberglass. Compared to foam insulation, cellulose has a lower R-value per inch, but is much less expensive; foam has a higher cost per equivalent R-value.
• Long-Term Cost Savings
  Cellulose's insulation qualities "can save homeowners 20 to 50 percent on their utility bills".
• Sound Insulation
  Noise reduction is achieved in three ways with cellulose. The first is that cellulose completely fills cavities leaving few air pockets for sound to travel in. The second is the cellulose materials ability to trap air. The significant difference between noise reduction with cellulose and fiberglass is its density. Cellulose is approximately three times denser then fiberglass. This helps deaden the sound through walls and between floor levels. Several installation options allow walls to have a Sound Transmission Class (STC) of 50 or greater. As a comparison, walls with fiberglass batts have an STC of 36-39, depending on stud and screw spacing.
• Mold and Pest Control
  The borates in cellulose insulation provide superior control against mold, insects, and pests such as rodents. Installations have shown that even several months of water-saturation and improper installation did not result in mold.
• Fire Retardation
  The borate treatment also provides cellulose with the highest (Class I) fire safety rating. This is an advantage over foams and fiberglass. In addition, fire will not cause toxic fumes.
  Cellulose Insulation is treated with fire retardant chemicals, keeps your home cool in the summer, and warms in the winter. All this adds up to big savings on your utility bills and a higher home resale value.
  AmericanEnergy Conservation Video "The Big Burn"
• Vapor Barrier
  A vapor barrier may not be needed with cellulose insulation. For example, recent studies have shown that air movement is the primary method by which excessive moisture can accumulate in mild marine climate such as Portland, OR, USA. An insulation that fills the wall cavity completely (such as cellulose or foam) can help prevent moisture problems. Recommendations against using vapor barriers with cellulose insulation are supported by studies, even though they classify cellulose as vapor permeable. In addition, cellulose acts to distribute moisture throughout the cavity, preventing the buildup of moisture in one area and helping to dry the moisture more quickly. Cellulose manufacturers do not recommend the installation of a vapor barrier with cellulose. Most city codes will require a vapor barrier for any external wall. Most US cities will consider an appeal of the requirement if proper reasoning is provided. In March of 2008 The US city of Portland, Oregon, approved an appeal to waive the requirement for a vapor barrier/retarder when using cellulose insulation. The appeal can be viewed in the Portland Bureau of Development Services search form by searching for appeal ID 4996. Fundamental to any appeal is mentioning that recent studies show air movement is the primary problem for vapor, that cellulose is an effective barrier to air movement, and that cellulose acts to diffuse vapor. - Wikipedia

Sustainable and Environmentally Preferable Properties

Cellulose insulation is growing in popularity, in part due to being one of the most environmentally preferable insulation types available.

• Recycled Content
  Cellulose is composed of 75-85% recycled paper fiber, usually post-consumer waste newsprint. The other 15% is a fire retardant such as boric acid or ammonium sulphate. Cellulose has the highest recycled content of any insulation available. By example, fiberglass has a maximum amount of 30% recycled content.
• Low-Toxicity and Environmental Impact of Raw Materials
  The non-recycled components of cellulose insulation are still environmentally preferable to the raw materials of most other insulation types, which are often petrochemical-based (this includes foam and fiberglass). Unlike foam insulations, many of which use HFC or HCFC blowing agents which have global warming potential hundred or thousands of times higher than that of carbon dioxide, cellulose does not produce significant gaseous emissions. Unlike fiberglass, cellulose does not use formaldehyde-based glues, which present a continuing hazard after installation due to off-gassing of formaldehyde. Cellulose has great advantages for industrial health and worker safety. Toxicity of the raw materials of most insulation types is typically highest during manufacture or installation. Neither is an issue with cellulose.
  The sole hazard for cellulose is categorization by OSHA as a dust nuisance, requiring a simple dust mask during installation. This compares very favorably to the potential NIOSH cancer risk of fiberglass.
• Embodied Energy
  The embodied energy of cellulose compared to all other insulation is by far the lowest. It requires 20 to 40 times as much energy to produce furnace-made insulation materials compared to cellulose. Cellulose is made by electrically powered machines while mineral insulation is made in furnaces. Cellulose is also made with locally available materials other than the fire retardant, while mineral insulation factories have to ship materials and products over greater distances. Cellulose insulation does use borates, which are mined in California and Turkey. While small quantities are used, this is a limited resource. Borax mining employs one of the cleanest mining techniques available. From a mining and natural resource perspective, cellulose is preferable to foam and fiberglass insulation.
• Insulation is Green
  All insulation helps make buildings more energy efficient. Using cellulose insulation can contribute to obtaining LEED credits in the US Green Building Council certification program. It can earn credit in two categories: the energy and atmosphere energy performance category and the materials and resources recycled content category. - Wikipedia

Additional Information

Cellulose Insulation Winning Market Share in Colorado, Built Green Colorado, Steve Andres, October 5, 2007.
http://www.builtgreen.org/articles/0209_cellulose.htm

Cellulose Insulation – A Smart Choice, Building Materials and Wood Technology, UMass - Amherst, Paul Fisette, 2005.
http://www.umass.edu/bmatwt/publications/articles/cellulose_insulation.html

According to DIY Network...

Blown-in cellulose is a popular alternative to fiberglass insulation. According to insulation specialist Richard Applegate, cellulose is a natural wood product, and 75 percent of what it's made from is recycled newspaper. Fire-retardant chemical additives give the material a class-1 fire rating, making it a very safe product.

One of the biggest advantages of using cellulose is its performance. In fact, because of its density, it has a higher R-rating than and outperforms many common insulation products. Its loose nature makes it easier to install into irregular spaces, creating a custom-fit monolithic seal over an entire area.

From both health and environmental perspectives, cellulose is considered a "green" product -- more ecologically sound than competing products. It doesn't contain formaldehyde, and cancer warnings are not required on its labeling. Since there are no glass fibers, as with fiberglass insulation, cellulose does not cause itch.

According to insulation specialist Richard Applegate, from both health and environmental perspectives, cellulose is considered a "green" product -- more ecologically sound than competing products. It's also highly effective and less costly than fiberglass.

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