Cellulose insulation

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Cellulose insulation Ecovata.jpg
Cellulose insulation
Cellulose insulation is often blown into building spaces through hoses from special blowing equipment in this case mounted inside a truck. Insulation Truck.jpg
Cellulose insulation is often blown into building spaces through hoses from special blowing equipment in this case mounted inside a truck.
insulation of the floor Cellulose insulation300.jpg
insulation of the floor
room wall Cellulose insulation.jpg
room wall

Cellulose insulation is plant fiber used in wall and roof cavities to insulate, draught proof and reduce noise. Building insulation in general is low-thermal-conductivity material used to reduce building heat loss and gain and reduce noise transmission.


History of cellulose insulation

The word cellulose comes from the French word cellule for a living cell and glucose which is a sugar.

The main house of US president Thomas Jefferson's plantation Monticello was insulated with a form of cellulose in 1772. [1] Cellulose was used more widely as an insulation material in Scandinavia from the 1920s. [2] Many types of cellulosic materials have been used, including newspaper, cardboard, cotton, straw, sawdust, hemp and corncob. 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 in the 1970s.

The market for insulation increased following the oil embargo of 1973–74, which caused energy costs for heating to skyrocket across the US, leading to increased interest in energy conservation measures. Insulation gained significant US 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 US homeowners who installed insulation.

While in 1976 there were roughly 100 cellulose insulation firms with 125 plants in the US, by 1978 there were more than 350 firms with more than 500 plants1. 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 rockwool 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 US 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. This led to the US Federal Consumer Products Safety Commission (CPSC) passing 16 CFR Part 1209, which set 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 costs incurred by increasing testing for fire resistance required by CPSC made cellulose more expensive, and the bad publicity helped decrease demand. Small producers of cellulose insulation were either unable to meet the testing requirements and went out of business, or they merged with other small manufacturers. In 1985 the CPSC asked Congress to repeal the flammability standard after further studies. By 1991 only 61 cellulose producers remained in the US. [3]

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, or were purposefully misleading and untrue .[ citation needed ]

Currently cellulose insulation has increased again in use in the United States. Part of the reason for this growth could be related to studies that suggest cellulose may actually protect a building from damage in a fire better than fiberglass because cellulose is denser and restricts the oxygen necessary to burn structural members. Several National Research Council Canada studies [4] 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 insulation.


Cellulose insulation is often made by hammer milling waste newspaper. The newspaper is treated with chemicals, such as boric acid, to retard the spread of fire.


Four major types of loose-fill cellulose products have been developed under a variety of brand names. These are generally characterized as dry cellulose, spray applied cellulose, stabilized cellulose, and low dust cellulose. These types are used in different parts of a building and for different reasons.

Dry cellulose (loose fill)

blowing equipment(Dry cellulose) Cellulose insulation200.JPG
blowing equipment(Dry cellulose)

Dry cellulose is used in retrofitting old homes by blowing the cellulose into holes drilled into the tops of the walls. 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 30%–40%. Look to the coverage chart on any product application instruction. R-value based on settled thickness. Use of given instruction charts are for estimating purposes only. Job conditions, application techniques and settings on equipment will influence actual coverage. Do not add water to this product. Due to variance in application moisture levels and temperatures cellulose will settle. 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. In addition, a dense-pack option can be used to reduce settling and further minimize air gaps. Dense-pack can only be done in a closed cavity by placing pressure on the cavity, and should be done only 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 (wet-spray cellulose)

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 [ citation needed ] 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. [5]

Stabilized cellulose

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. [5]

Low-dust cellulose

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).

Advantages of cellulose insulation

Thermal performance

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[ clarification needed ] 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%. [6] 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.[ citation needed ]

Long-term cost savings

Annual 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". [7]

Sound insulation

Insulation reduces sound travelling through walls and between floor levels. Cellulose provides mass and damping. This reduces noise in 2 ways, it reduces the lateral movement 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.

Mold and pest control

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. [8]

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 in the US.

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.

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, US. [9] 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. [10]

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. [10]

Most US city codes require a vapor barrier for any external wall. Most US cities will consider an appeal against the requirement if proper reasoning is provided. In March 2008 the US city of Portland, Oregon, approved an appeal to waive the requirement for a vapor barrier/retarder when using cellulose insulation. [11] Fundamental to any appeal is stating 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.


The R-value of 3.6 to 3.8 per inch[ citation needed ] is good but not the best.[ citation needed ] Material cost per R-value is good but labor cost goes up because it takes more material and time to install than fiberglass insulation at the same R-Value[ citation needed ].


Cellulose contains small particles which can be blown into the house through inadequate seals around fixtures or small holes. [12] [13]

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, US 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.


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. [14] Ceiling structures should be inspected for signs of weakness before choosing a material for insulating the ceilings of existing structures. [15]


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. [16]


There is some evidence of increased mold infestation inside buildings insulated with wet spray dense pack cellulose especially when used with a vapor barrier. [17]

Environmental properties

Insulation of any type helps make buildings more energy-efficient. Depending on the structure and manufacturer, using cellulose insulation could contribute to obtaining LEED credits from the US Green Building Council certification program. [18]

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

Average toxicity and environmental impact of raw materials

Although cellulose is considered a safe material, it has a high amount of chemicals in it's 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.

Embodied energy

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.[ citation needed ] Cellulose is made by electrically powered machines while mineral insulation is made in fuel powered furnaces,[ citation needed ] reducing this advantage to a degree, as electricity generation is less than 50% efficient. Cellulose is made with locally available paper,[ citation needed ] 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.

See also

Related Research Articles

<span class="mw-page-title-main">Thermal insulation</span> Minimization of heat transfer

Thermal insulation is the reduction of heat transfer between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with specially engineered methods or processes, as well as with suitable object shapes and materials.

<span class="mw-page-title-main">R-value (insulation)</span> Measure of how well an object, per unit of area, resists conductive flow of heat

In the context of construction, the R-value is a measure of how well a two-dimensional barrier, such as a layer of insulation, a window or a complete wall or ceiling, resists the conductive flow of heat. R-value is the temperature difference per unit of heat flux needed to sustain one unit of heat flux between the warmer surface and colder surface of a barrier under steady-state conditions. The measure is therefore equally relevant for lowering energy bills for heating in the winter, for cooling in the summer, and for general comfort.

<span class="mw-page-title-main">Radiant barrier</span>

A radiant barrier is a type of building material that reflects thermal radiation and reduces heat transfer. Because thermal energy is also transferred by conduction and convection, in addition radiation, radiant barriers are often supplemented with thermal insulation that slows down heat transfer by conduction or convection.

<span class="mw-page-title-main">Glass wool</span> Insulating material made from fibers of glass

Glass wool is an insulating material made from glass fiber arranged using a binder into a texture similar to wool. The process traps many small pockets of air between the glass, and these small air pockets result in high thermal insulation properties. Glass wool is produced in rolls or in slabs, with different thermal and mechanical properties. It may also be produced as a material that can be sprayed or applied in place, on the surface to be insulated. The modern method for producing glass wool was invented by Games Slayter while he was working at the Owens-Illinois Glass Co.. He first applied for a patent for a new process to make glass wool in 1933.

<span class="mw-page-title-main">Insulating concrete form</span>

Insulating concrete form or insulated concrete form (ICF) is a system of formwork for reinforced concrete usually made with a rigid thermal insulation that stays in place as a permanent interior and exterior substrate for walls, floors, and roofs. The forms are interlocking modular units that are dry-stacked and filled with concrete. The units lock together somewhat like Lego bricks and create a form for the structural walls or floors of a building. ICF construction has become commonplace for both low rise commercial and high performance residential construction as more stringent energy efficiency and natural disaster resistant building codes are adopted.

Low emissivity refers to a surface condition that emits low levels of radiant thermal (heat) energy. All materials absorb, reflect, and emit radiant energy according to Planck's law but here, the primary concern is a special wavelength interval of radiant energy, namely thermal radiation of materials. In common use, especially building applications, the temperature range of approximately -40 to +80 degrees Celsius is the focus, but in aerospace and industrial process engineering, much broader ranges are of practical concern.

<span class="mw-page-title-main">Exterior insulation finishing system</span> Non-load bearing building cladding

Exterior insulation and finish system (EIFS) is a general class of non-load bearing building cladding systems that provides exterior walls with an insulated, water-resistant, finished surface in an integrated composite material system. In Europe, systems similar to EIFS are known as External Wall Insulation System (EWIS) and External Thermal Insulation Cladding System (ETICS).

<span class="mw-page-title-main">Vapor barrier</span> Damp proofing material in sheet form

A vapor barrier is any material used for damp proofing, typically a plastic or foil sheet, that resists diffusion of moisture through the wall, floor, ceiling, or roof assemblies of buildings and of packaging to prevent interstitial condensation. Technically, many of these materials are only vapor retarders as they have varying degrees of permeability.

<span class="mw-page-title-main">Superinsulation</span> Method of insulating a building

Superinsulation is an approach to building design, construction, and retrofitting that dramatically reduces heat loss by using much higher levels of insulation and airtightness than normal. Superinsulation is one of the ancestors of the passive house approach.

<span class="mw-page-title-main">Housewrap</span> Material used to protect buildings

Housewrap, also known by the genericized trademark homewrap, generally denotes a modern synthetic material used to protect buildings. Housewrap functions as a weather-resistant barrier, preventing rain or other forms of moisture from getting into the wall assembly while allowing water vapor to pass to the exterior. If moisture from either direction is allowed to build up within stud or cavity walls, mold and rot can set in and fiberglass or cellulose insulation will lose its R-value due to heat-conducting moisture. House wrap may also serve as an air barrier if it is sealed carefully at seams.

<span class="mw-page-title-main">Cavity wall</span> Type of wall with a hollow center

A cavity wall is a type of wall that has a hollow center. They can be described as consisting of two "skins" separated by a hollow space (cavity). The skins typically are masonry, such as brick or cinder block. Masonry is an absorbent material that can slowly draw rainwater or even humidity into the wall. One function of the cavity is to drain water through weep holes at the base of the wall system or above windows. The weep holes allow wind to create an air stream through the cavity that exports evaporated water from the cavity to the outside. Usually, weep holes are created by separating several vertical joints approximately two meters apart at the base of each story. Weep holes are also placed above windows to prevent dry rot of wooden window frames. A cavity wall with masonry as both inner and outer skins is more commonly referred to as a double wythe masonry wall.

<span class="mw-page-title-main">Duct (flow)</span> Conduit used in heating, ventilation, and air conditioning

Ducts are conduits or passages used in heating, ventilation, and air conditioning (HVAC) to deliver and remove air. The needed airflows include, for example, supply air, return air, and exhaust air. Ducts commonly also deliver ventilation air as part of the supply air. As such, air ducts are one method of ensuring acceptable indoor air quality as well as thermal comfort.

<span class="mw-page-title-main">Building insulation</span> Material to reduce heat transfer in structures

Building insulation is material used in a building to reduce the flow of thermal energy. While the majority of insulation in buildings is for thermal purposes, the term also applies to acoustic insulation, fire insulation, and impact insulation. Often an insulation material will be chosen for its ability to perform several of these functions at once.

<span class="mw-page-title-main">Building insulation material</span>

Building insulation materials are the building materials which form the thermal envelope of a building or otherwise reduce heat transfer.

<span class="mw-page-title-main">Wool insulation</span>

Wool insulation is made from sheep wool fibres that are either mechanically held together or bonded using between 5% and 20% recycled polyester adhesive to form insulating batts, rolls and ropes. Some companies do not use any adhesives or bonding agents, but rather entangle the wool fibers into in high R-Value, air capturing knops that hold themselves together. Natural wool insulation is effective for both thermal and acoustic insulation. The wool is often sourced from the less expensive black wools of the UK and Europe. Batts are commonly used in the walls and ceilings of timber-frame buildings, rolls can be cut to size for lofts, and ropes can be used between the logs in log homes. Wool knops are installed loosely in attics or in walls as a blow-in-blanket system utilizing a fiber mesh to hold the wool in place during the blow in process.

<span class="mw-page-title-main">Spray foam</span>

Spray foam(expanding foam in the UK) is a chemical product created by two materials, isocyanate and polyol resin, which react when mixed with each other and expand up to 30-60 times its liquid volume after it is sprayed in place. This expansion makes it useful as a specialty packing material which forms to the shape of the product being packaged and produces a high thermal insulating value with virtually no air infiltration.

<span class="mw-page-title-main">Rigid panel</span>

Rigid panel insulation, also referred to as continuous insulation, can be made from foam plastics such as polyurethane (PUR), polyisocyanurate (PIR), and polystyrene, or from fibrous materials such as fiberglass, rock and slag wool. Rigid panel continuous insulation is often used to provide a thermal break in the building envelope, thus reducing thermal bridging.

<span class="mw-page-title-main">Rainscreen</span>

A rainscreen is an exterior wall detail where the siding stands off from the moisture-resistant surface of an air/water barrier applied to the sheathing to create a capillary break and to allow drainage and evaporation. The rainscreen is the cladding or siding itself but the term rainscreen implies a system of building. Ideally the rainscreen prevents the wall air/water barrier from getting wet but because of cladding attachments and penetrations water is likely to reach this point, and hence materials are selected to be moisture tolerant and integrated with flashing. In some cases a rainscreen wall is called a pressure-equalized rainscreen wall where the ventilation openings are large enough for the air pressure to nearly equalize on both sides of the rain screen, but this name has been criticized as being redundant and is only useful to scientists and engineers.

<span class="mw-page-title-main">Insulated glazing</span> Construction element consisting of at least two glass plates

Insulating glass (IG) consists of two or more glass window panes separated by a space to reduce heat transfer across a part of the building envelope. A window with insulating glass is commonly known as double glazing or a double-paned window, triple glazing or a triple-paned window, or quadruple glazing or a quadruple-paned window, depending upon how many panes of glass are used in its construction.

Interstitial condensation is a type of condensation that may occur within an enclosed wall, roof or floor cavity structure, which can create dampening.


  1. Brett French. "Cellulose Insulation Used In Historic Yellowstone Photography Store". The Billings Gazette , May 30, 2019. Accessed June 8, 2021.
  2. Bozsaky, Dávid (2010). "The historical development of thermal insulation materials". Periodica Polytechnica Architecture. 41 (2): 49–56. doi: 10.3311/pp.ar.2010-2.02 . ISSN   1789-3437.
  3. Cellulose Insulation Manufacturers Association, http://www.cellulose.org/
  4. Fire Resistance Tests on Cellulose and Glass Fiber Insulated Wood Stud Shear Walls, Kodur, V.K.R.; Sultan, M.A.; Latour, J.C.; Leroux, P.; Monette, R.C., IRC-IR-806, , archive-backup Quote: "...Results from fire tests F21, F21A, F22A and F32 can be used to indicate the effect of insulation types on the fire resistance of load-bearing wood stud shear walls (see Figure 16). The failure of the glass fibre insulated wall assembly (F21 and F21A) occurred at 42 and 43 minutes respectively, while the failure of the rock fibre and cellulose insulated wall assemblies occurred at 54 and 51 minutes respectively. As shown in Figure 18, these results suggest that the use of cellulose fibre insulation provides a higher fire resistance compared to glass fibre insulation, but a lower fire resistance compared to rock fibre insulation..."
  5. 1 2 ICC Legacy Report ER-2833 – Cocoon Thermal and Sound Insulation Products, ICC Evaluation Services, Inc., http://www.icc-es.org
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  10. 1 2 "Discover why homes and building don't require an air/vapor barrier when using cellulose insulation". Cellulose Insulation Manufacturers Association. Retrieved 6 September 2022.
  11. "Appeal 4996". The City of Portland, Oregon. 26 March 2008.
  12. "Cellulose Insulation Problems". Archived from the original on 2011-11-04. Retrieved 2011-04-07.
  13. "NTP Toxicity Study Report on the Atmospheric Characterization, Particle Size, Chemical Composition, and Workplace Exposure Assessment of Cellulose Insulation" (PDF). National Toxology Program. U.S. Department of Health and Human Services. August 2006. Archived (PDF) from the original on February 22, 2022. Retrieved November 8, 2022.
  14. Weights of Building Materials Archived May 16, 2011, at the Wayback Machine Boise Cascade Engineered Wood Products Tech Note GE-1, p. 1, retrieved Sept. 17, 2010
  15. How to Insulate a Ceiling Bonneville Power Administration, retrieved Sept. 17, 2010
  16. "SCI Engineering Newsletter report" (PDF). Archived from the original (PDF) on July 16, 2011.
  17. Godish, TJ; Godish, DR (2006). "Mold infestation of wet spray-applied cellulose insulation". J Air Waste Manag Assoc. 56 (1): 90–5. doi: 10.1080/10473289.2006.10464434 . PMID   16499151.
  18. LEED. U.S. Green Building Council, 19 Nov. 2015. Web. <http://www.usgbc.org/leed>

Further reading