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 utilize an environmentally harmful blowing agent, such as Enovate HFC.
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 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.
Cellulose insulation is prone to create too much dust that is blown into the house through inadequate seals around fixtures or minute holes. This is mostly found in rooms that are used frequently and can be a real health problem, especially if you live in a carpet-less home where dust stays airborne longer. Even those old constructions with tiny holes in the wall, may cause the cellulose dust and asbestos to be blown into the rooms and duct work. This is a blown cellulose insulation problem. Also, removal can be very costly depending on square footage.
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
Information provided by Wikipedia VIA: wikipedia.org