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Tradical Hemcrete

Tradical Hemcrete is a non-structural, rigid, insulating, composite wall fill comprised (by weight) of about 38% hemp and 62% lime-based binder… Read more
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  • 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.

  • 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.

  • Just how low the VOC level needs to be for a given product to qualify for inclusion in GreenSpec depends on the product category. For most products, we require certification to California’s health-based emissions standard, CDPH Std Method v1.1 standard (also referred to as California Section 01350), which tests a product’s resultant VOC concentrations in the space after a given period of time. For wet-applied products like paints, caulks, and adhesives, we still also look for VOC content instead of, or in addition to, verified low emissions; this is because emissions testing doesn’t adequately test initial offgassing, and VOC content is currently the only widely available proxy.

Brent Ehrlich
Products Editor

Tradical Hemcrete is a non-structural, rigid, insulating, composite wall fill comprised (by weight) of about 38% hemp and 62% lime-based binder. The dried stems of hemp are mixed with the lime-based binder and the mix is placed into removable wall forms. Suitable for moderate climates, the walls insulate at R-2.3 per inch, according to the manufacturer, and are typically 12-inches thick, so they provide about R-28. The Hemcrete walls are finished on the exterior with lime stucco and on the interior with lime plaster. The Tradical lime binder is manufactured in the U.K. by Lime Technology, Ltd. and the industrial hemp is sourced from England, where it can be grown legally. (It is illegal to grow hemp in the U.S., but American Lime Technology is working to find a more local source in Canada.)

Read more on this product in "BuildingGreen's Product of the Week"

Concrete is an integral component of our buildings and infrastructure but production of its key ingredient, portland cement, is a major source of the world’s anthropogenic carbon dioxide emissions and can also lead to emissions other hazardous byproducts such as mercury and nitrogen oxides.

The environmental footprint and performance of concrete can be improved by replacing a portion of the portland cement with fly ash, ground granulated blast furnace slag, silica fume, rice husks, or other supplementary cementitious materials. Recycled concrete, glass, and slag can be used to reduce the impact of mining of virgin aggregate and the amount of construction material sent to landfills. Lightweight aggregate can lower the weight of the structure and some can provide thermal insulation.

Products listed by GreenSpec incorporate recycled content, have improved durability, provide insulation, or have other innovative environmental qualities.

Earthern unit masonry, including adobe bricks and compressed earth blocks (CEBs). can offer a variety of advantages over more mainstream construction techniques, such as timber frame or concrete. For one, it is commonly made onsite from readily available materials.

Adobe is a natural building material common to the American Southwest. It can be very durable if protected from erosion; many Native American adobe structures built hundreds of years ago are still standing. Made from soil that has suitable sand and clay content and then air-dried in the sun, adobe bricks typically have extremely low greenhouse gas emissions and embodied energy. Walls made of adobe bricks are most often protected from the weather with a parge coat of stucco or plaster, or large overhangs.

While adobe bricks are commonly made onsite without stabilizers, most commercially available adobe bricks are “stabilized” with portland cement or asphalt additives, adding to their expense, and depending on the proportion of stabilizer, adding significantly to their embodied carbon.

CEBs are a mixture of sand, silt, clay, and organic material, and can usually be made from soil at or near the building site. The addition of portland cement or another stabilizer may be recommended based on soil characteristics and performance needs, but this will add to the embodied impacts of the blocks.

Soil is loaded into CEB machines, which can typically press several thousand blocks per day. In addition to avoiding the impact of shipping materials to the site, this systems provides cost advantages, with avoiding purchasing and shipping costs.

The state of New Mexico developed a code regulating standard practices for CEB construction. The code technically only regulates construction in New Mexico, but is being used in other regions. When considering CEB construction, be sure to review the code and understand the important concepts, such as the difference between stabilized and unstabilized CEB, and when each are appropriate.

Due to the relatively low impact of these materials and construction methods, GreenSpec lists adobe blocks and related products, as well as CEB presses.

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.

LEED Credits

EAc1: Optimize Energy Performance

EAp2: Minimum Energy Performance

MRc6: Rapidly Renewable Materials

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