Cellulose insulation

Dry cellulose blowing equipment.

Dry cellulose is used in retrofitting old homes by blowing the cellulose into holes drilled into the tops of the walls.[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. This form of application does settle as much as 13% to 20% over time.[6] This settling could leave gaps in a wall as the insulation compacts vertically, or it could leave space between a floor and the insulation beneath it.[5] A dense-pack option can be used to reduce settling and further minimize air gaps. Dense-pack places pressure on the cavity, and should be done by an experienced installer.

Loose fill in walls is an antiquated technique of using cellulose in wall cavities. The home performance industry and its accrediting bodies support the dense-pack standard of insulating wall cavities, which does not settle. This method stops the stack effect and convective loops in wall cavities.

Spray-applied cellulose is used for applying cellulose to new wall construction. The differences are the addition of water to the cellulose while spraying as well as adding some kind of moisture retardant such as chlorine to prevent mold cultures. In some cases the insulation might also mix in a very small percentage of adhesive or activate a dry adhesive present in the cellulose. Wet-spray allows application without the need for a temporary retainer. In addition, wet-spray allows for an even better seal of the insulated cavity against air infiltration and eliminates settling problems. Wet-spray installation requires that the wall be allowed to dry for a minimum of 24 hours (or until maximum of 25% moisture is reached) before being covered.[7]

Stabilized cellulose is used most often in attic/roof insulation. It is applied with a very small amount of water to activate an adhesive of some kind. This reduces settling and decreases the amount of cellulose needed. This can prove advantageous at reducing the overall weight of the product on the ceiling drywall helping prevent possible sag. This application is ideal for sloped roofs and has been approved for 5:12 (41.66%) slopes.[7]

The last major type of cellulose insulation on the market is low-dust variety. Nuisance levels of dust are created during application of most types of dry insulation causing the need for simple dust masks to be worn during installation. This kind of cellulose has a small percentage of oil or similar dust dampener added. This may also be appropriate to homes where people are sensitive to newsprint or paper dust (though new dust will not be created after installation).

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. The thermal conductivity of loose-fill cellulose is approximately 40 mW/m·K (R-value: metric R2.6 per 100 mm; imperial R3.8 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. 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. The cellulose insulation lost 26.4% less heat energy over time compared to the fiberglass insulation. It also was shown to tighten the structure more than 30%.[8] Subsequent real world surveys have cellulose performing 20–30% better at reducing energy used for heating than fiberglass.

Compared to closed cell, Polyurethane foam insulation (R=5.5 to 6.5 per inch), cellulose has a lower R-value per inch, but is much less expensive; foam has a higher cost per equivalent R-value.

Yearly savings from insulating vary widely and depend on several factors, including insulation thickness, original wall performance, local climate, heating/cooling use, airtightness of other building elements, and so on.

One installer claims cellulose insulation "can save homeowners 20 to 50 percent on their utility bills".[9]

Insulation reduces sound travelling through walls and between floor levels. Cellulose provides mass and damping. This reduces noise in two ways: it reduces the lateral vibration of sheetrock and attenuates the passage of sound along cavities. Cellulose is approximately three times denser than fiberglass, providing a slight improvement in sound reduction.

The borates in cellulose insulation provide added control against mold. Installations have shown that even several months of water saturation and improper installation did not result in mold.[10]

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 advertised in the U.S. as having pesticidal effects.

The borate treatment also gives cellulose the highest (Class I) fire safety rating. Many cellulose companies use a blend of ammonium sulfate and borate.

Building codes in most American cities require a vapor barrier or retarder on the inside of an exterior wall in order to prevent moisture from the warm interior from condensing inside the wall and causing mold or rot. However, many building officials will waive the requirement when a good reason is provided. 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.[12] A cellulose industry group argues that by filling the wall cavity completely, cellulose limits the flow of warm, humid air into the wall cavity and thus limits the amount of moisture accumulated to an amount that cellulose can manage without harm. 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.[13][14]

Cellulose contains small particles which can be blown into the house through inadequate seals around fixtures or small holes.[15][16]

Not all insulation installers are experienced with cellulose. Some installation considerations specific to cellulose include how to dense-pack loose-fill dry cellulose; how to apply stabilized (partly wet) on sloped surfaces, and the proper time required for wet-spray cellulose to dry.

Building codes concerning cellulose insulation may vary regionally, so local building officials should be consulted before planning an installation.

If improperly installed, loose fill cellulose could settle after application. In some situations this could leave areas of wall uninsulated. With correct training in installation methods and quality control techniques this is ruled out by installing to tested densities preventing any future settlement.

For a given R-value, loose cellulose weighs roughly three times as much per square foot as loose fiberglass.[17] Ceiling structures should be inspected for signs of weakness before choosing a material for insulating the ceilings of existing structures.[18]

Many cellulose companies use a blend of ammonium sulfate and borate for fire retardation. Although ammonium sulfate is normally odorless, unexplained emission of ammonia and a resulting ammonia smell has been found in some cases.[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.[20]

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. For example, fiberglass has a maximum amount of 50% recycled content.

Although cellulose is considered a safe material, it has a high amount of chemicals in its composition, thus generating an average to high amount of volatile organic compounds(VOC), much higher than other alternative materials as batts, EPS, XPS or spray foam.

The embodied energy of cellulose insulation is the lowest of the popular insulation types. 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 fuel powered furnaces, reducing this advantage to a degree, as electricity generation is less than 50% efficient. Cellulose is made with locally available paper, while mineral insulation factories ship materials and products over greater distances.

Cellulose insulation uses borates for fire retardation. Borates are a non-renewable mined product.