Insulation: Thermal Performance is Just the Beginning
InsulSafe ® 4, made by CertainTeed Corporation, is a formaldehyde-free, loose-fill, fiberglass insulation suitable for open-blow attic applications. The product contains recycled glass cullet and carries Greenguard™ certification for low emissions.
This article provides a survey of insulation materials, beginning with an examination of what insulation is and how it works. Much of the article focuses on life-cycle considerations for different insulation materials: environmental and health issues associated with resource extraction, manufacture, use, and disposal.
Understanding Insulation
To really understand insulation materials, you have to understand the basics of heat flow. There are three primary mechanisms of heat flow: conduction, convection, and radiation. Thermal conduction is the movement of heat from direct contact: one molecule is activated (excited) by heat and transfers that kinetic energy to an adjacent molecule. We generally think of conduction occurring between solid materials—the handle of a hot skillet conducting its heat to your hand, for example—but thermal conduction also occurs with liquids and gases.Convection is the transfer of heat in liquids and gases by the movement of those molecules from one place to another. As air is warmed, it expands, becomes more buoyant, and rises—a process called natural convection. Forced convection is the distribution of warm air by use of a fan or air handler.
Finally, radiation is the transfer of heat from one body to another via the propagation of electromagnetic waves. A warmer body will radiate heat to a cooler body. When you sit in front of a fireplace and look into the fire, your face is warmed by the radiant transfer of energy from that heat source to your face. That radiant energy is not affected by air currents and occurs even across a vacuum—as we know from lying in the sun!
Most insulation materials function by slowing the conductive flow of heat. Materials with low thermal conductivity more effectively block heat flow than materials with high thermal conductivity. The R-value of an insulation material measures its resistance to heat flow. R-value is the inverse of U-factor, which is a measure of heat transfer, usually measured in Btu/hr·ft 2·°F or W/m 2·°C. Most insulation materials work by trapping tiny pockets of air (or some other gas). The performance of that insulation material is determined primarily by the conductivity of the air, or other gas, in those spaces. If convection is prevented, a 1" (25 mm) air space has a conductivity of about 0.18 Btu/hr·ft 2·°F (1.02 W/m 2·°C). Its resistance to conductive heat loss, the inverse of that value, is R-5.5 per inch (RSI-38/m). With fiber insulation materials, such as fiberglass, cellulose, and cotton, pockets of air are trapped between the fibers. With cellular insulation materials, such as polystyrene, polyisocyanurate (polyiso), and polyurethane, the air—or other gas—is trapped within the plastic cells comprising the foam.
While resistance to conductive heat flow is the primary operative property of insulation materials, convection and radiation can come into play as well. With polyiso insulation, for example, according to Richard Roe of the Atlas Roofing Corporation in an August 2002 article in Interface magazine, 60–65% of the heat transfer is attributed to the conductivity of the blowing agent gases trapped in the cells, while 20–25% is attributed to the thermal conductivity of the solid polymer matrix, and 10–15% is attributed to radiation. One key design features of an insulation material is keeping the air pockets small enough to limit convection within those spaces and radiation across those spaces. With fiber insulation materials, the fibers have to be packed densely enough to effectively stop airflow through the material. (Air blowing through the insulation would carry heat by convection.)
With insulation materials that incorporate radiant barriers (foil-faced batt insulation, radiant-barrier bubble-pack insulation, and reflective barriers on rigid foam sheathing), the reflective surface functions by reducing radiant heat transfer. To function in this capacity, the reflective surface has to be next to an air space. The surface may function by reflecting heat radiation or (more commonly) by emitting less radiant energy from it. This is why a radiant barrier can reduce heat loss even when the reflective (low-emissivity) surface is facing the cold side.
Note that air leakage is a type of convection. Air leakage allows conditioned air to leak out of a building and unconditioned air to leak in—bypassing the insulated portions of the envelope. In older homes air leakage around windows, through poorly fitting doors, and across poorly detailed walls can sometimes account for over half of the total wintertime heat loss! Air leakage can also occur through an insulation material, which can reduce that material's effective R-value. Loose-fill fiberglass, for example, usually allows more airflow than does cellulose insulation.
Life-Cycle Considerations with Insulation Materials
In this portion of the article, we examine the four primary life-cycle stages of any building material: raw material acquisition; manufacturing; the use phase, including indoor air quality concerns; and end-of-life disposal and recyclability. In each of these life-cycle stages we highlight key differences among insulation materials and discuss recent developments. Summaries of the key life-cycle considerations are presented by insulation material in the accompanying table.Raw material acquisition
All Johns Manville fiberglass insulation is now produced with formaldehyde-free binders.
Most U.S. fiberglass insulation has a minimum 20–30% recycled content. Owens Corning, for example, has been third-party certified by Scientific Certification Systems (SCS) to contain at least 30% recycled content—4% post-consumer and 26% pre-consumer, according to Jim Worden of the company. Johns Manville has an SCS-certified minimum recycled content of 25%; CertainTeed claims a minimum recycled content of 20–25% to meet U.S. Environmental Protection Agency (EPA) requirements under the Comprehensive Procurement Guidelines (CPG); and Knauf Fiberglass claims a minimum 20% recycled content, all of it post-consumer. Recycled-content information for Guardian Fiberglass was not available.
Mineral wool. Mineral wool is made from both iron ore blast-furnace slag (an industrial waste product from steel production) and rock such as basalt. In 2003 the mineral-slag wool industry used 514 million pounds (233 million kg) of slag. This is down 45% from the slag use in 1992. Mineral-slag wool production is down in part because building codes are shifting away from the passive fire resistance that mineral wool provides toward active sprinklering of buildings.
Cellulose. Cellulose insulation is made primarily from post-consumer recycled newspaper, with up to 20% ammonium sulfate and/or borate flame retardants. While cellulose insulation used to be one of the highest-value uses of old newspaper, today dozens of de-inking plants in North America turn old newspaper into new newsprint. Producing cellulose insulation from old newspaper can be referred to as downcycling; from an environmental standpoint, turning a waste product back into a new form of the same material is preferable to turning it into a lower-grade material. (Note that producing fiberglass insulation from beverage bottles or glass cullet is also downcycling.)
Plastic foam insulation. Plastic foam insulation materials, including extruded polystyrene (XPS), expanded polystyrene (EPS), polyisocyanurate, and the various types of spray polyurethane insulation, are all produced primarily from petrochemicals. Both natural gas and petroleum are common feedstocks, and both have significant environmental impacts associated with their extraction, refining, and transport.
At least two open-cell, spray polyurethane insulation products are manufactured in part from soybeans. Two-component BioBase 501 (see EBN Vol. 12, No. 9) and HealthySeal 500 are produced with soy oil comprising approximately 40% of the polyol component. (Polyurethanes are produced by reacting an isocyanate with a polyol, which is a type of alcohol.) The resultant polyurethane foam ends up being about 25% soy-derived and 75% petrochemical-derived.
Polystyrene. Recycled polystyrene can be incorporated into polystyrene foam insulation fairly easily, since polystyrene is a thermoplastic. At least one EPS insulation product contains recycled polystyrene: Polar 10 from Polar Industries is made with up to 40–60% post-industrial recycled content (see EBN Vol. 10, No. 2). The only XPS product that includes recycled content today is Owens Corning Foamular®, which is SCS-certified to contain a minimum of 15% pre-consumer recycled polystyrene.
Polyisocyanurate. Polyiso insulation incorporates a relatively small amount (9–10%) of recycled content to comply with CPG minimums. A portion of the polyol used in polyiso is produced from recycled PET bottles. The polyiso industry is one of the largest users of recycled, mixed-color PET bottles, according to the Polyisocyanurate Insulation Manufacturers Association (PIMA). The foil facings on many polyiso boardstock products may also contain some recycled content.
Bonded Logic's cotton insulation is manufactured from pre-consumer recycled denim waste.
Cotton insulation. Cotton insulation is made today by two manufacturers. Bonded Logic, Inc. and Inno-Therm, Inc. make batt insulation products from pre-consumer recycled denim scrap. The cotton or cotton-polyester fibers are treated with a nonhalogenated flame retardant. UltraTouch, produced by Bonded Logic, contains approximately 85% pre-consumer recycled fiber saturated with borate flame retardants to provide fire resistance. Inno-Therm is believed to be using a mix of borate and ammonium sulfate flame retardants. In addition to its use in batt insulation products, cotton insulation is used by Payless Insulation, Inc. in insulated flexible duct products; Bonded Logic supplies the cotton insulation for these products.
Cementitious foam insulation. The totally inorganic, cementitious Air Krete ® is produced from magnesium oxide, derived from seawater, and from a ceramic talc mined in Governor, New York. While essentially the same material as it was when last covered in EBN ( Vol. 6, No. 7), Air Krete has undergone some modest refinements, according to vice-president Bruce Christopher. "We have continued to improve both the product and the equipment for installation," he told EBN. But he noted that friability—the fragility of the cured foam—remains their biggest challenge. "If there is a downside to Air Krete, it's its friability." Despite its resistance to the idea, the company may decide to add a little plastic to make it less friable, said Christopher. The challenge in adding plastic would be maintaining the superb fire resistance of the insulation material. While cost is highly variable, depending on location, size of the job, and other factors, it averages 30–50¢ per board foot, according to Christopher.
Air Krete remains a very good alternative to another foamed-in-place insulation material used primarily for insulating masonry block, Tripolymer ® foam, produced by the C. P. Chemical Company. Tripolymer foam is a foamed phenol-formaldehyde insulation—a material that some manufacturers of urea-formaldehyde foam insulation (UFFI) switched to after formaldehyde emissions from UFFI led to its discontinuance in the 1970s.
Radiant barriers. Radiant barriers could be produced with recycled aluminum, but this is rarely if ever done, because very pure aluminum is needed to achieve the thin foils. Recycled polyethylene, however, can be used for the foam that is sometimes used with radiant barriers. Low-E ® Insulation, produced by Environmentally Safe Products, Inc., uses polyethylene foam with 40% post-consumer recycled content. In its TempShield™ radiant insulation product, Sealed Air Corporation uses 20% recycled-content cellular polyethylene for the insulation laminated between layers of reflective foil. A number of manufactured panel products have reflective facings glued to one side.
Manufacturing and transport
Fiberglass. Fiberglass insulation is manufactured with binders (typically phenol-formaldehyde) that hold the glass fibers together. The only fiberglass insulation material that did not contain a binder, Owens Corning's Miraflex™ (see EBN Vol. 4, No. 1) was pulled off the market late in 2004. Manufacture of Miraflex was actually discontinued at the beginning of 2003, according to Gale Tedhams, Owens Corning's product manager for residential insulation, but enough material had been stockpiled to sell it through 2004—mostly through Lowe's stores. "It just had a very limited market," Tedhams told EBN. Owens Corning did not promote the health benefits of not having a binder but focused on the packaging benefits—rolls of the insulation take up half the space of standard fiberglass. While the product carried a "slight price premium," according to Tedhams, it was "very expensive to manufacture." See additional discussion of binders used in fiberglass insulation under "Use phase and IAQ concerns."Cellulose. Because cellulose is inherently combustible, flame retardants are required to make it an acceptable material for building insulation. As has been the case for the past ten years, the primary flame retardants used in cellulose insulation are ammonium sulfate, borax, and boric acid. According to Daniel Lea, executive director of the Cellulose Insulation Manufacturers Association (CIMA), these additives are typically used in combination, though a few manufacturers offer products that use all-borate retardants.
Polyisocyanurate. The biggest environmental news in foam boardstock insulation has been the elimination of HCFC-141b in polyiso. The industry completed the transition from that ozone-depleting compound to the blowing agent pentane at the end of 2002. (Some manufacturers continued using stockpiled HCFC-141b in early 2003 while plant modifications were completed.) The transition to an ozone-safe formulation was a big step for polyiso, and it renders the product significantly better environmentally than extruded polystyrene (XPS), which in North America is still made with an HCFC blowing agent.
In an industry that is generally slow to change, these changes in polyiso have been dramatic. In 1992 polyiso was all produced with CFC-11. By mid-1993 the polyiso industry had shifted completely to HCFC-141b, which has only about 10% the ozone depletion potential of CFC-11. Atlas Industries then led the transition away from HCFCs, introducing its ozone-friendly AC-Ultra™ in February 1998 (see EBN Vol. 7, No. 5). By May 2001 the company had fully converted three of its plants to pentane (see EBN Vol. 10, No. 5), with others converted early in 2002.
Polystyrene. Polystyrene has some fairly troubling chemical precursors in its production. The polystyrene used in both XPS and EPS is made by reacting ethylene (from natural gas or crude oil) with benzene (from crude oil, via naphtha catalytic reforming) to produce ethyl-benzene. The ethyl-benzene is converted into vinyl-benzene or styrene monomer, which is then polymerized into polystyrene. Benzene is listed in the 10th Report on Carcinogens, put out by the National Toxicology Program of the U.S. Department of Health and Human Services, as a "known carcinogen." The International Agency for Research on Cancer (IARC) of the World Health Organization lists benzene as a "confirmed human carcinogen" and styrene monomer as a "possible human carcinogen." Some material safety data sheets (MSDS) for polystyrene list residual styrene monomer as a constituent of the foam at levels up to 0.2%. While benzene is also used in polyiso and polyurethane production, these insulation materials are less likely than polystyrene to contain residual toxic chemicals.
Extruded polystyrene. XPS and EPS differ in how the foam is expanded—and they use quite different blowing agents. EPS has long been made with non-ozone-depleting pentane, but XPS still relies on HCFCs. Though the XPS industry led the charge in replacing CFCs with far-less-damaging HCFCs, it is today the only type of boardstock insulation that remains harmful to stratospheric ozone. Amofoam (now Pactiv) was the first company to switch from CFC-12 to HCFC-142b, in 1990, and the entire XPS industry completed that transition in 1992. The transition away from HCFC-142b is not likely in the U.S. until close to the 2010 EPA deadline for doing so (see EBN Vol. 11, No. 7), according to Worden at Owens Corning. While European manufacturers of XPS shifted to either HFC-134A or carbon dioxide in 2002, more stringent energy standards and different construction systems in North America make the same sort of conversion more difficult here, says Worden. European XPS is a higher-density product with a lower R-value.
Expanded polystyrene. Expanded polystyrene (EPS) continues to be made with non-ozone-depleting pentane as the expanding agent. Some manufacturers are using a low-pentane formulation that results in lower pentane emissions. (While not an ozone-depleting compound, pentane can generate ground-level smog.) The more distributed production of EPS, compared with XPS, may reduce shipping energy consumption to some extent.
Flame retardants and polystyrene. All foam plastic insulation materials rely on flame retardants to meet fire-resistance standards. EPS and XPS are produced using the brominated flame retardant HBCD (hexabromocyclododecane) at concentrations of 0.5–2.0% by weight. HBCD is not the focus of as much attention as another class of brominated flame retardants (PBDEs), but some evidence indicates that it is more bioaccumulative than PBDEs and just as likely to be toxic to humans (see EBN Vol. 13, No. 6).
Flame retardants and polyisocyanurate. Ironically, until recently flame retardants were not used in most polyiso insulation. With HCFC blowing agents, this thermoset plastic foam was able to achieve the required Class I fire ratings without any added flame retardant. But with the substitution of pentane blowing agents for HCFC-141b, manufacturers now must add flame retardants. Although manufacturers rarely divulge their formulations (and can apparently get around the requirement to list the flame retardant in the MSDS because it is part of one component or the other (the polyol or isocyanate), the most common flame retardant used in polyiso today is believed to be TCPP (tris(chloropropyl) phosphate), a compound that relies on both phosphorous and chlorine as the fire-retarding components. The typical concentration in the foam insulation is 5–14% by weight. While a halogenated compound, TCPP is much less likely to be a persistent bioaccumulative toxin than HBCD, according to the PBT Profiler software from EPA.
Spray polyurethane. While polyiso manufacturers had to eliminate their use of HCFC-141b by January 1, 2003, manufacturers of closed-cell (high-density) spray polyurethane were given an extension for the transition to non-ozone-depleting blowing agents. HCFC-141b for spray polyurethane cannot be sold after December 31, 2004, though polyurethane installers can use inventoried HCFC-based chemicals until July 1, 2005, according to Ken Gayer, the global business manager for foam blowing agents at Honeywell Specialty Materials, which produces the non-ozone-depleting blowing agent HFC-245fa under the tradename Enovate 3000.
Most spray polyurethane companies are converting to Honeywell's HFC-245fa. While significantly more expensive than HCFC-141b, the resultant foam achieves similar energy performance. The ozone depletion potential of HFC-245fa is zero, but the global warming potential is similar to that of HCFC-141b. Hydrocarbon blowing agents are avoided with spray polyurethane because of flammability concerns and difficulties with the vapor pressure, according to Gayer.
Low-density, open-cell polyurethane produced by Icynene is material-
efficient and uses water as the blowing agent.
Flame retardants and spray polyurethane. Both closed-cell (high-density) and open-cell (low-density) polyurethane insulation contain flame retardants, but these are non-brominated flame retardants. While manufacturers are reluctant to share this information, the best available information indicates that the two flame retardants most commonly used in spray polyurethane are TCPP, which contains chlorine but not bromine, and RDP (resorcinol-bis-diphenylphosphate), which is totally halogen-free.
Use phase and IAQ concerns
Fiberglass and mineral wool. Concerns about mineral and glass fibers possibly being carcinogenic have been widely publicized over the past ten years—especially by competing industries. These concerns resulted in cancer warning labels being required for most products, but more recently these concerns are waning. In October 2001, IARC changed its classification for fiberglass and mineral wool from "possible human carcinogen" to "not a known human carcinogen." This change has allowed mineral wool (slag wool and rock wool) manufacturers to drop the warning labels.Fiberglass insulation continues to carry the cancer warnings because, in addition to the IARC listing, the National Toxicology Program added glass fibers to its Report on Carcinogens in 1990. According to Angus Crane, the vice president and general council for NAIMA, glass fibers were added to the NTP possible-carcinogen list because of the IARC-reported studies. Now that IARC has dropped the possible-carcinogen listing for glass fibers, the material is likely to be dropped from the NTP list. NAIMA has petitioned NTP to delist glass fibers, but that process typically takes several years. Crane hopes to see the listing removed in late 2005 or early 2006. If and when that happens, the industry will petition the State of California to remove the requirement under Proposition 65 that fiberglass insulation products include a warning about cancer.
Meanwhile, the carcinogenicity of formaldehyde, which could be released in very small quantities from the phenol-formaldehyde binder used in most fiberglass insulation, has recently been upgraded. In June 2004, IARC changed its classification of formaldehyde from a "probable human carcinogen" to a "confirmed human carcinogen." Most of this binder is volatized and dissipated during a baking stage of the manufacturing process, but residual formaldehyde may remain in the product. Johns Manville, one of the five major producers of fiberglass insulation in North America, switched to 100% acrylic binder for its fiberglass insulation product line in 2002 (see EBN Vol. 11, No. 3). The other major fiberglass insulation manufacturers have all had their products certified as low-emitting by Greenguard™.
Mineral wool. For cavity-fill and attic applications, rock wool and slag wool are similar to fiberglass in look and feel, though the density is greater and the sound control better. The fire resistance of mineral wool is also significantly better than that of fiberglass, because of both the higher density and the significantly higher temperatures required for melting. While these fire-resistance properties used to be a major selling point, greater reliance on sprinklers in buildings, rather than passive fire resistance, is resulting in decreased use of mineral wool, according to Crane of NAIMA.
For below-grade applications, one rigid mineral-wool product, Roxul drainboard, offers superb performance, owing to its hydrophobic properties and its excellent drainage characteristics (see EBN Vol. 4, No. 6). This material has never been actively marketed in the U.S., but Roxul products in general are becoming more widely available here.
Cellulose. Cellulose insulation has never been required to carry indoor air quality warnings, and the fiberglass and mineral wool industries remain upset that their products have come under greater scrutiny than cellulose. "Our competitors have not gone through the testing," said Angus Crane of NAIMA. "It is dangerous to assume that an untested material is safe," he told EBN. The editors at EBN continue to take the position that all fiber insulation products (fiberglass, mineral wool, and cellulose) are safe if properly installed, and we would much prefer to see insulation manufacturers focus on the positive benefits of all insulation, rather than potential risks of their competitors' products. The health concerns with cellulose range from inhalation of dust during installation to VOC emissions from printing inks (which are now almost entirely vegetable-based) and limited evidence of toxicity of boric acid flame retardants. For more on health issues with cellulose insulation see EBN Vol. 2, No. 5.
As for installation and performance, cellulose insulation has evolved considerably over the past 20 years. According to Daniel Lea of CIMA, the average installed density of cellulose insulation has dropped from 2.6 pounds per cubic foot (42 kg/m 3) in 1984 to 1.6 pcf (26 kg/m 3) today. "R for R, today's cellulose insulation products are almost 40% lighter than those of 1984," said Lea. Most cellulose insulation today is being installed as "cellulose wall-cavity spray," a process that has sometimes been referred to as "wet-spray" cellulose. CIMA is trying to discourage the use of the term wet-spray because it implies a process that is far wetter than is the case. "I think there is a perception that the material is applied almost as a fibrous papier-mâché," said Lea. "That is far from the case; if you were to touch wall spray seconds after it's applied, you probably couldn't tell that water was added during the installation process," he said. The typical installed moisture content today is 30–35%, according to Lea, while a moisture content as high as 60% was not uncommon 15 years ago.
Fiber insulation installation. Quality dust masks or respirators should be used while installing fiberglass, mineral wool, and cellulose. (Cotton insulation is the only fiber insulation material that can be installed safely without protective measures.) Building design and detailing should ensure that fibers cannot enter forced-air distribution or ventilation systems. Airtight construction practices should be used to ensure that fiber insulation stays where it was installed.
Polystyrene. Indoor air quality concerns with XPS and EPS are similar to concerns addressed previously relating to manufacturing: the potential release of residual styrene monomer and flame retardants. The brominated flame retardants used in polystyrene present a greater health concern than the nonbrominated flame retardants used in polyisocyanurate, spray polyurethane, and cellulose insulation.
Polyisocyanurate. Now that polyiso is no longer produced with HCFCs, it is the environmentally preferred rigid boardstock insulation for above-grade applications. (Polyiso is not recommended for below-grade applications because it can absorb moisture.) Polyiso manufacturers disagree as to whether rigid foam produced today with hydrocarbon blowing agents achieves an R-value comparable to that of the older material made with HCFC-141b. The conductivity of the hydrocarbon blowing agent is higher than that of HCFC-141b, and this has led Dow Chemical to downgrade the rated R-values for all of its polyiso insulation, including Thermax ®. However, Richard Roe of Atlas Roofing argues that the smaller cell size of foam produced with hydrocarbon blowing agents, the slower diffusion rate of the hydrocarbon out of the polymer cells, and the lower absorption of the hydrocarbon blowing agent by the polymer collectively result in better long-term R-value stability.
Most polyiso manufacturers are now using new long-term thermal resistance (LTTR) values for reporting aged R-values. This method was adopted in Canada in mid-2002 and in the U.S. in January 2003. This method produces 5-year aged R-values that are lower than the 6-month aged R-values that had previously been reported. The bottom line is that the rated long-term stabilized R-value of polyiso is now between R-6 and 6.5 per inch (RSI-42 to 45 per meter), depending on thickness and facings.
Closed-cell polyurethane. Closed-cell, high-density polyurethane is a very good performer owing to the low-conductivity gas in the cellular structure. It is used both for cavity installation and as an insulating roofing material, which is typically referred to as spray polyurethane foam or SPF. The closed-cell structure gives SPF structural properties. There should be no significant impact on R-value with the shift to non-ozone-depleting HFC-245fa blowing agent, which is becoming the industry standard. Polyurethane also exhibits superb adhesive properties and good compressive strength.
Open-cell polyurethane. Open-cell polyurethane is most commonly installed into open cavities, though formulations are available for filling closed cavities from holes at the top. This is a nonstructural foam, though these materials seal very well, and their flexibility allows for some movement of the framing materials as shrinkage and expansion occur. These properties make them very effective insulation materials for older buildings.
Both closed-cell and open-cell polyurethane must be installed by trained professionals. Special care is required to ensure the safety of insulation installers working with these materials; other people should not be in the space while polyurethane insulation is being installed. Once cured, polyurethane insulation is considered by most IAQ experts to be quite inert.
End-of-life reuse and recyclability
Loose-fill and batt insulation. It is difficult to salvage loose-fill or batt insulation and reuse it, though this can be done. Virtually no fiber insulation is recycled after use in buildings—due to contamination with dust and other materials. Scrap insulation generated during installation can be collected and reused quite easily. Insulation Materials – Summary of Environmental and Health Considerations
Rigid boardstock insulation. Rigid insulation can be salvaged and reused if it is protected during removal. For roof insulation applications, reuse is most feasible when protected-membrane or inverted roof configurations are used (see EBN Vol. 7, No. 10). In this system, a non-water-absorbing rigid insulation, such as XPS, is laid on top of the roof membrane, and ballast is installed on top of the insulation. When re-roofing is required, the insulation can be removed and stored for safekeeping, then reinstalled after the new roof membrane is laid down.
Of the rigid insulation materials, only polystyrene can be recycled. This thermoplastic can be melted and re-expanded into either polystyrene insulation or packaging. Unfortunately, very little polystyrene is being recycled currently. Polyiso and polyurethane cannot be recycled because these foams are thermoset plastics.
Final Thoughts and Recommendations
Insulation is a key component of any green building. More important than the decision of what type of insulation to install is the decision of how much insulation should be installed. From an environmental standpoint, a thicker layer of a relatively nongreen insulation material is almost always better than an inadequate thickness of the greenest insulation material available. This point cannot be over-emphasized.However, assuming that adequate R-values can be achieved, choosing a green insulation material over a nongreen one can be a very good decision. The accompanying table should help to identify materials that meet your needs and satisfy the environmental priorities of your project.
Summary recommendations:
• Provide the highest feasible insulation levels.• With lower R-value materials, increase insulation thickness.
• Avoid extruded polystyrene due to the ozone-depletion potential of blowing agent.
• Except where moisture may be an issue, use polyiso instead of either XPS or EPS.
• Rigid mineral wool, such as that made by Roxul, is a very good foundation insulation material due to its superb drainage properties.
• With highly conductive framing systems, especially steel, minimize thermal bridging by wrapping the frame with a layer of rigid board insulation.
• Choose high-recycled-content insulation materials when doing so will not result in significant loss of R-value compared with other materials.
• With roof insulation, consider a protected-membrane roof so that insulation can be reused.
• Address air leakage and moisture resistance in insulation detailing. A good source of information on building science issues is http://www.buildingscience.com/.
• For chemically sensitive individuals, test potential insulation materials for reaction before installation.
• Choose an insulation contractor who recycles scrap insulation.
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