Growing and harvesting our building materials would be a great way to move toward a closed-loop system rather than a linear path from extraction to disposal. Doing so holds the promise of true sustainability and regeneration of ecosystems instead of damage to them.
Unfortunately, biobased materials today can be at least as problematic as any other material. Intensive land use, chemical use, fuel use, nutrient runoff, and other pollution are among the impacts of agriculture; add to that competition between food crops and those used for building materials or fuel. We would like to see sustainable use of biobased materials, but improving practices and figuring out how to assess and document more sustainable practices will take a long time. There is no ready equivalent to FSC for biobased materials that aren’t wood, although certification to “organic” standards or other sustainable agriculture standards can provide guidance in some cases.
At the same time, we don’t want to exclude biobased products that are typically responsibly sourced just because they don’t have a certification—particularly where they replace more problematic materials. GreenSpec continues to give preference to rapidly renewable alternatives to materials that present greater concerns. Examples of rapidly renewable materials in GreenSpec include linoleum, cork, and textiles such as wool, sisal, and organic cotton.
SheepBATT, SheepROLL, SheepROCK, and SheepFILL Insulation
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Before specifying efficient heating and cooling equipment, it’s important to do what we can to reduce heating and cooling loads. Insulation is one of the key products to consider here, but because there are so many insulation products on the market, we look for additional benefits. Examples include cellulose insulation with recycled content, mineral wool insulation with no flame retardants, and fiberglass insulation with no formaldehyde binders. Other products in this area are high-performance windows and glazings, products that contribute to building airtight envelopes, products that reduce thermal bridging, and window-retrofit products.
With products in this area under constant development, we are always refining our approach. For example, as we have learned about insulation products with hazardous flame retardants and blowing agents that have high global warming potential, we have removed those products from GreenSpec, pending manufacturing changes. We encourage building professionals to pressure manufacturers for those changes through specification language and purchasing decisions.
Black Mountain USA sells a variety of sheep wool insulation products including batts, rolls, loose fill, and a rigid wool and plaster panel. Batts and rolls come in 16" and 24" widths, and thicknesses of 3.5", 5.25", and 5.75". The products' R-value is 3.7 per inch. The wool currently is sourced from Great Britain, but the company is in the process of securing a U.S. source.
Blanket, or batt, insulation can be manufactured using fiberglass, mineral wool, or cotton. Fiberglass is made primarily from silica spun into glass fibers held together with a phenol-formaldehyde (PF) binder— although formaldehyde-free products are commonly available. Most fiberglass insulation today has at least 30% recycled-glass content, with some manufacturers using as much as 40% post-consumer recycled glass from bottles.
Mineral wool insulation is made from molten slag (a waste product of steel production), natural rock (such as basalt and diabase), or a combination of the two, and a PF binder to hold the fibers together. Mineral wool has a higher density than fiberglass, so it has better sound-blocking properties. It is also more fire-resistant than fiberglass.
Cotton insulation is made from post-industrial recycled or post-consumer recycled cotton textiles, such as denim, with synthetic fibers added to maintain loft. Low-toxic flame retardants similar to those used in clothing are added. Unlike fiberglass and mineral wool, there are no mineral microfibers to cause respiratory and skin irritation.
Blanket insulations, especially fiberglass products, are typically inexpensive, but require meticulous installation to minimize air leaks around openings and where wires or pipes extend through wall cavities that can compromise the wall’s overall performance. Fiberglass may also be less effective than many insulation types under very cold conditions, due to its relatively low density and air movement through it—though this has been a greater problem with loose-fill fiberglass in attics.
Products listed here have high recycled content, reduced indoor air quality concerns, or superior performance in particular applications based on their air-tightness or management of moisture.
Rigid board insulation, usually made from plastic foam, glass fibers, or mineral wool, is a critical component in many new or retrofit energy-efficient buildings. Rigid board insulation typically provides high R-value for a given thickness and can be applied across the surface of walls, roofs, or foundations to reduce thermal bridging through framing, foundations, and other structural components.
Foam board insulation is petroleum-derived and uses a blowing agent for expansion. Polyisocyanurate—or “polyiso”—foam board typically has foil facing and has the highest R-value of any common insulation material. Polyiso boards are made with hydrocarbon blowing agents that are non-ozone-depleting and have negligible global warming potential (GWP).
Extruded polystyrene (XPS) is non-ozone-depleting, although XPS in North America is produced today with a blowing agent (HFC-134a) that has high GWP. (Most European manufacturers have converted to very-low-GWP hydrocarbon blowing agents, while North American manufacturers have been unwilling to have the R-value per inch drop as a result of a similar change.)
XPS and expanded polystyrene (EPS) are manufactured using a number of hazardous chemicals, including benzene and the brominated flame retardant HBCD—which is a persistent, bioaccumulative toxin that is slated for elimination in Europe. Because of the health and environmental concerns surrounding these materials, GreenSpec does not list rigid polystyrene insulation as a stand-alone product. However, because energy performance is a high priority with any building, use of XPS or EPS may be appropriate when those are the only options available.
Alternatives to rigid foam include rigid mineral wool, rigid fiberglass, and foamed cellular glass. It may also be possible to redesign building enclosure systems to utilize spray polyurethane foam (SPF) or minimize thermal bridging in other ways so that cellulose or other fiber insulation products can be used without an energy penalty.
Mineral wool board is a versatile insulation made from molten slag (a waste product of steel production) or natural rock (such as basalt or diabase), held together with a phenol formaldehyde binder. Mineral wool has a higher density than fiberglass, is more resistant to fire, and is better at blocking sound. It is appropriate for foundation wall insulation and, in highest-density form, may be considered for use under concrete slabs (although such applications may need special approval by building officials).
While expensive, cellular glass (Foamglas) is another option. Its high compressive strength and moisture properties make it appropriate for below-grade applications, especially sub-slab applications where XPS currently dominates the market.
Rigid fiberglass is made similar to fiberglass batts, but formed into denser boardstock. A shift to a non-formaldehyde binders has not been as rapid with rigid insulation products as it has with batts, but some manufacturers are making that transition. Concentration of the binder is higher in rigid boardstock than in batt insulation.
Note that board insulation products vary widely not only in R-value but also in permeability, moisture resistance, insect resistance, fire resistance (and need for flame retardant additives), and end-use applications. Selection of these products can be complex and confusing. More detail is offered in the BuildingGreen Guide to Insulation Products and Practices.
Products listed here have at least one of the following attributes: post- and/or pre-consumer recycled-content, reduced off-gassing, avoidance common hazardous ingredients, high durability, and blowing agents with little or no global warming potential.
Blown insulation can be any fiber insulation material that is blown into place, usually in a wall cavity or attic. The most common blown insulation materials are cellulose and fiberglass, but mineral wool, sheep’s wool, and other materials are also used.
Cellulose insulation has several environmental advantages. Most products contain 75%–85% recycled newspaper (usually post-consumer) and borate and/or ammonium sulfate flame retardants, which are benign in comparison with other common flame retardants.
Dry cellulose can be blown into a closed framing cavity in a “dense-pack” application, or blown or poured into the floor cavity of an attic or ceiling. “Stabilized” cellulose, used primarily in attic floor applications, contains a small amount of acrylic binder to prevent settling and shrinkage. For information on damp-spray cellulose, see 07 21 29 – Sprayed Insulation. Rental equipment is commonly available for applying loose-fill cellulose, while hiring a contractor is necessary for a dense-pack application.
The energy performance of dense-pack cellulose is comparable to that of high-density fiberglass batts at roughly R-3.7 per inch, but cellulose insulation generally fills cavities more completely—especially around wires or pipes, or in oddly sized framing cavities—and so is more effective at preventing convection heat losses.
Loose fiberglass is most commonly blown into closed cavities or applied through a specialized mesh that has been stretched across the inner face of framing members; a form including binder can also be sprayed into an open cavity (see also 07 21 29 – Sprayed Insulation). Fiberglass and mineral wool can release respirable fibers into the air. While these fibers are less likely to be carcinogenic than they were in older formulations, they are respiratory irritants. Blown fiberglass and mineral wool should only be installed if the fibers can be prevented from getting into occupied space or air distribution systems.
Products listed here have recycled content, are derived from agricultural waste, offer superior moisture or air leakage performance, or impart lower indoor air quality concerns than other products.
LEED Credits
EAc1: Optimize Energy Performance
EAp2: Minimum Energy Performance
MRc6: Rapidly Renewable Materials
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