The stone industry adopts a new sustainability standard.
By Meg Calkins, FASLA
In 14 Patterns of Biophilic Design, Bill Browning, an environmental designer and founder of Terrapin Bright Green, cites “material connection with nature” as a significant principle. In other words, materials from nature, with minimal processing, can be used to construct the built environment—reflecting the local geology and connecting people to a place and natural setting. More than any other material, stone fulfills this “pattern”—often seamlessly settling a built landscape into the larger natural context. Yet in some cases, heavy stone can travel thousands of miles between harvest and use—offering absolutely no connection to the local natural landscape and creating a substantial environmental footprint.
Stone holds great potential to be a highly sustainable construction material for use in paving, stairs, and walls. It can be extremely durable, with relatively low embodied energy (energy used to produce a material), and nontoxic. However, a study from the University of Tennessee estimates that more than half of all dimension stone—defined as any stone that has been cut or shaped for use in construction—is imported, primarily from China, India, and Brazil, owing to far lower labor costs and fewer worker safety regulations, which combine for a lower product cost. Some of this stone might have been harvested in the United States, sent overseas for processing, then returned as “imported stone.” Minimal records of stone harvest, sales, and processing make it challenging to track stone’s path to market. Additionally, environmental impacts from waste and water use in stone quarrying and manufacture are not insignificant. Fortunately, a new standard from the Natural Stone Council (NSC) and the American National Standards Institute (ANSI) offers criteria for reducing the environmental impacts of stone harvest and processing and requires a chain of custody for stone so consumers can know for sure the path their “local” stone has traveled.
The stone quarrying process is often lumped together with metal mining’s heavy blasting and toxic runoff, but Kathy Spanier, the marketing director at Coldspring in Minnesota and a participant in the development of the new stone standard, emphasizes that it is not similar at all. In metal mining, the stone is blasted apart to get at the metals. This can result in acid mine drainage from metals and toxic runoff from the blasting explosives. Conversely, the aim of stone quarrying is to gently lift large blocks of stone out of the quarry. Explosives are used, but minimally, and quarry stone does not usually contain toxic metals, so runoff is more benign.
As a consultant on the new NSF/ANSI standard, Jason McLennan, the board chair of the Living Future Institute, observed that habitat impacts of stone quarrying are a fraction of those in the logging industry, as they are not nearly so land consumptive. This is partially because stone deposits can be quite deep—granite deposits, for example, can extend down 300 feet—allowing for the harvest of large volumes of material in a relatively small surface area. That said, there are still habitat impacts from removal of vegetation and soil, air quality impacts from airborne particulates, and quarry restoration is still largely unregulated, meaning excavation sites are often simply abandoned.
Waste is a major environmental impact of the quarrying and fabrication process for dimension stone. For example, it is not uncommon for 30 feet of “overburden” (soil and loose stone) to be removed before limestone suitable for dimension stone use is harvested. A 2008 study by the U.S. Department of Transportation, a major consumer of stone waste, estimates that 175 million tons of quarrying waste is produced in the United States annually. Waste varies widely by stone type and deposit, and the University of Tennessee study estimates that between 3 percent and 93 percent of total quarry material is waste, and that between 6 percent and 69 percent of further waste is produced from fractured or damaged slabs during the fabrication phase.
The market for beneficial reuse of stone waste is quite strong, as it is used for aggregate applications such as road base, backfill, and in concrete and asphalt. Large blocks of stone that are inappropriate for dimension stone are used whole for benches, walls, and other monumental landscape applications.
After harvesting, there can be multiple steps to achieve dimension stone. In primary processing, the large blocks lifted from a quarry are cut into slabs using a variety of saw types. For rough-cut dimension stone, this may be the only step, and it often happens near the quarry. But for most applications, the next steps are finishing the stone to the required surface specification and exact dimensions. Some of this finishing is mechanical, but some is completed by hand, hence the need for skilled labor.
Some smaller quarry owners don’t engage in processing of their stone; instead they sell the large blocks to fabricators who may be located far from the quarry or even overseas. Where stone must be cut to very precise dimensions for applications with tight tolerances, it is more likely that it will be shipped overseas, where labor costs are low for skilled stone workers. This, combined with low shipping costs, makes economic if not environmental sense. From an environmental standpoint it can increase the embodied energy by fivefold. It can also be a social sustainability concern, as there may be human rights violations in the workers’ wages and safety conditions.
Molly Bourne, ASLA, a principal at MNLA (formerly Mathews Nielsen Landscape Architects), is aware of the environmental impacts of imported stone. “We are not interested in stone that has made a large loop around the world, so we try to write our specs so that stone from overseas doesn’t get used,” says Bourne. On public bid jobs, they try to thoroughly describe stone qualities, such as density and appearance, that they know will result in the use of local or regional stone. Bourne adds that it can be very challenging to work with stone cut in China when some dimensions or field conditions are not quite right. Very few contractors have the skills to adjust the fine cuts on site, so it has to be installed as is or reordered, which can slow construction substantially.
Computer numerical control (CNC) stone fabrication is starting to bring dimension stone processing back to the United States as the price of CNC technology and equipment comes down. CNC technologies are used for cutting, edging, polishing, grooving, and carving dimension stone. Martina Diamantini of Citco in Milan, producers of Zaha Hadid’s 2012 sculptural stone panels, says that CNC milling is the most common method used by their firm for three-dimensional stone works, and CNC water jets are used for two-dimensional stone carving.
Custom fabrication can be simplified using CNC technologies, and more complex forms can be produced. Along with reduced equipment costs, CAM software, which interfaces with the equipment, has become more user friendly, resulting in ease of use for even the novice. This won’t necessarily bring the price down, but eventually it could mean that stone is fabricated closer to the site rather than overseas, and it could allow smaller fabricating companies to compete with larger international outfits.
A new app called the Stones of North America Stone Selector was created by the Natural Stone Institute to assist designers in locating locally quarried and fabricated stone. It is a searchable database where users can input a zip code and search for quarries within a certain distance. It is still possible, however, that the stone could be harvested near a project site but sent elsewhere for processing.
The NSC and ANSI have recently released a quarry certification standard called ANSI/NSC 373-2013 Sustainable Production of Natural Dimension Stone. Coldspring’s Kathy Spanier was one of the founders of the standard along with a multidisciplinary group including academics, green building consultants, and stone industry businesses. Work on the standard began 12 years ago when the NSC recognized that stone was being left out of the sustainable materials conversation despite its obvious potential as a green material.
The multiattribute standard is designed to encourage sustainability practices in the natural dimension stone industry. It offers a series of environmental, social, and human health metrics for stone quarries and fabricators to improve their practices. Certification under the standard is third-party verified by NSF International, and quarries must periodically recertify to maintain their status.
A chain of custody is also required for certification under the standard. Much like a lumber chain of custody, this requires documentation of the stone at every phase of its journey to the project site, providing assurance to the consumer that the stone has not been sent overseas or across the country for processing without their knowledge.
To date, five companies with multiple quarries are certified under the standard: TexaStone Quarries, Coldspring, Northern Stone Supply, Stony Creek Quarry, and Michels Stone. Some of these companies operate multiple quarries, and not all of each company’s quarries are certified. For instance, Coldspring has certified its main facility in Cold Spring, Minnesota, and plans to certify quarries in California next. Spanier believes the growing adoption of Leadership in Energy and Environmental Design (LEED) v4 and the Sustainable Sites InitiativeTM (SITES®) should encourage more stone quarries and fabricators to engage in stone certification, as certified stone can contribute to achievement of credits.
Given that durability is one of stone’s most significant attributes, the importance of detailing stone structures for deconstruction and reuse should not be ignored, as stone can be used over and over again. Designing stone structures for deconstruction can contribute to SITES and LEED v4 credits. Ronald “Chip” Trageser, FASLA, a managing principal with OJB Landscape Architecture, set large blocks of stone paving at Enterprise Plaza in Houston directly on paver pedestals, holding them in place with nothing but gravity and the weight of the stone. There has been no movement in the 10 years the plaza has been in place, but the stone will be easily removed when the time comes. Trageser also used Z clips to attach stone veneer to plaza walls. These stainless steel clips minimize or eliminate the need for mortar, which will also facilitate deconstruction.
Taken together, the new standards, innovations in stone-working technology, and greater transparency in the stone industry will contribute to the sustainability performance of stone. Additionally, capitalizing on the natural durability of stone through detailing for longevity of structures, deconstruction, and reuse can put stone front and center in the sustainability conversation.
Meg Calkins, FASLA, is a professor in the Department of Landscape Architecture at Ball State University. She is the author of Materials for Sustainable Sites and the editor of The Sustainable Sites Handbook.
An earlier version of this article was updated to provide a revised link to the Stones of North America reference website; it is now hosted by the Natural Stone Institute, which was created by a recent merger of the Building Stone Institute and the Marble Institute of America.