Advantages and Disadvantages of Blown in Attic Insulation
Advantages and Disadvantages of Blown in Attic Insulation
Thermal Performance of Attic Insulation
The thermal performance of loose filled cellulose compares favorably to other types of attic insulation. The thermal conductivity of loose-fill cellulose is approximately 40 mW/mK (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
By insulating your loft using cellulose, it'squalities can save homeowners 20 to 50 percent on their utility bills
Mold and Pest Control
The borates in cellulose insulation provide superior control against mold. Installations have shown that even several months of water-saturation and improper installation did not result in mold.
It is a common misconception that the mere presence of crude borates in cellulose insulation provides pest control properties to the product. While boric acid itself does kill self-grooming insects if ingested, it must be presented to an insect in both sufficient concentration and in an ingestible form in order to achieve insect fatality. Proper testing of products containing borates must be performed in order to determine whether dosage and presentation are sufficient to kill insects. Once tested, registration with the EPA as a pesticide is required before a product may be touted as having pesticidal capabilities.
Fire Retardation
The borate treatment also gives cellulose the highest (Class I) fire safety rating. Many cellulose companies use a blend of ammonium sulfate and borate. Although ammonium sulfate is normally odorless, unexplained emission of ammonia and a resulting ammonia smell has been found in some cases
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 climates. An insulation that fills wall cavities 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.
Disadvantages of Attic Insulation
Cellulose has few disadvantages. As compared to other insulation options, the R-Value of 3.6 to 3.8 per inch is very good but not the best (though it competes well in cost per R-Value). Spray foam has many of the same benefits as wet-spray cellulose (such as sealing the cavity), while having advantages in R-value and rigidity and air sealing. However, many spray foams have undesirable environmental qualities as many products release greenhouse gases, including many sold as being "green," which often use Enovate HFC as the blowing agent.
Installation Expertise and Building Codes
In some areas it can be difficult to locate installers that are experienced with cellulose. An experienced installer understands how to correctly dense-pack loose fill dry cellulose, how to best apply stabilized (partly-wet) cellulose on sloped surfaces, and the proper time required for wet-spray cellulose to dry.
As with other non-batt insulation, city and regional/state building codes may not be updated for cellulose insulation. Homeowners should call the city to verify that the insulation will be approved, and it may be necessary to provide product specifications to the city. This is not difficult, and the installer and the manufacturer should both be willing to handle this process, saving the homeowner any true effort.
Most building codes require a vapor barrier, and it can be hard to convince some cities that one is not required for cellulose. In this case, an appeal (usually a quick process) may be necessary. Otherwise, vapor barriers can be installed. Options for a vapor barrier include plastic sheeting (fairly low environmental footprint due to the thin layer needed) or PVA paint (contains toxins and other qualities undesirable from an environmental standpoint).
Wet-Spray Drying Time
Wet-spray provides the advantage of a better sealing of the insulated cavity and superior rigidity. However, the moisture from a wet-spray insulation requires a longer drying time before the drywall/sheet-rock is applied to a newly insulated wall. This drying time is usually reduced by the use of large space heaters that are run for a few days to weeks, depending on ambient humidity. The installer should use a moisture meter to verify acceptable in-wall moisture levels before any drywall is applied. From an environmental and energy efficiency perspective, wet-spray is well worth the extra heating and time. This extra timing needs to be considered as part of the building schedule for new or remodel projects.
Weight
For a given R-value, loose cellulose weighs roughly three times as much per square foot as loose fiberglass. Ceiling structures should be inspected for signs of weakness before choosing a material for insulating the ceilings of existing structures
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