Cellulose insulation
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 United States in the 1970s.
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.
Due to complaints by retailers, contractors and consumers about price, safety and quality control problems, the U.S. 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, although there were no reliable national statistics.
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 costs incurred by increasing testing for fire resistance required by CPSC made cellulose more expensive, and the bad publicity helped decrease demand.
The newspaper is treated with chemicals, such as boric acid, to retard the spread of fire and to make the paper fiber less attractive to pests.
[5] It can also be blown into a new wall construction by using temporary retainers or netting that is clamped in place then removed once the cellulose has reached the appropriate density.
The home performance industry and its accrediting bodies support the dense-pack standard of insulating wall cavities, which does not settle.
The differences are the addition of water to the cellulose while spraying as well as adding some kind of moisture retardant such as chlorine [citation needed] to prevent mold cultures.
The thermal performance of loose filled cellulose compares favourably to other types of low cost insulation, but is lower than that of polyurethane and polyisocyanurate foams.
Other important aspects are how well the building envelope is sealed[clarification needed] from air infiltration, convective airflows, and thermal bridging.
Dense pack cellulose can seal walls from air infiltration while providing the density to limit convection, when installed properly.
The University of Colorado School of Architecture and Planning did a study that compared two seemingly identical test structures, one insulated with cellulose and the other with fiberglass.
[10] It is a common misconception that the mere presence of crude borates in cellulose insulation provides pest control properties to the product.
Proper testing of products containing borates must be performed in order to determine whether dosage and presentation are sufficient to kill insects.
In March, 2008, the city of Portland, Oregon, granted a waiver of the requirement for a vapor barrier or retarder when using cellulose insulation.
[11] This appeal cited industry guidance that the combination of an exterior vapor retarder (as required by code) and an interior one could trap moisture in the wall, leading to damage.
Recent studies have shown that even with a vapor retarder, excessive moisture can get into the wall by the movement of air around improperly sealed penetrations such as electrical outlets and can lights.
[19] There is some evidence of increased mold infestation inside buildings insulated with wet spray dense pack cellulose especially when used with a vapor barrier.
Depending on the structure and manufacturer, using cellulose insulation could contribute to obtaining LEED credits from the US Green Building Council certification program.
Cellulose is made with locally available paper,[citation needed] while mineral insulation factories ship materials and products over greater distances.
