November 3, 2016
by Stephanie Vierra, Assoc. AIA, LEED AP
Sustainable, high-performance building continues to be the desired model for design, construction, and operations in both the public and private sector. Initially, the movement was a response to the 2005 Energy Policy Act, which set the standards to mean “a building that integrates and optimizes all major high-performance building attributes, including energy efficiency, durability, life cycle performance, and occupant productivity.” Materials and systems choices can also have an impact on the aesthetics, accessibility, and security of a project, while simultaneously affecting long-term maintenance and operating costs.
High-performance design carefully looks at all these issues through an integrated process and over the life cycle for which the buildings are designed and intended to perform. Measurement and verification of the established performance criteria is essential—monitoring and managing a building’s performance over time helps ensure its long-term success, value, and return on investment (ROI).
Like a domino effect, one change or refinement can trigger multiple savings or benefits. More design professionals and building owners have begun to understand the positive impacts that high-performance projects have on the environment, the economy, and society because they are balanced, integrated, and built to last. So how does natural stone fit into this model?
Natural stone and high-performance design
Designers, contractors, owners, and building managers have an opportunity to seek out materials to meet their design and sustainability objectives and support the long-term performance of their projects. While the market is flooded with many new material and product choices that have green attributes, stone has been used for centuries.
Natural stone can be an excellent material choice because of its durability, low maintenance, recyclability, and natural aesthetic features that can be incorporated into any masonry projects easily and effectively. Through the ages, granite, marble, limestone, sandstone, travertine, slate, and many other stones have been chosen for their wide range of color, grain, texture, and material properties for use in landscaping, sculpture, structure, cladding, flooring, and countertops.
Outlining key performance goals early ensures the most appropriate stone is chosen and considered through operations and maintenance (and even eventual reuse). This goes beyond selecting the material itself, to considering how it will be quarried, finished, installed, and maintained. It also involves considering which other materials will interact with the stone, and how they will all meet the same performance goals. To ensure the best result, the implementation of green building and performance requirements and standards must be communicated and coordinated with the entire project team, including the stone supplier, fabricator, and installer.
The natural stone industry is advancing the use of best practices to refine the art and craft of stone masonry and improve the efficiency of the quarrying, fabrication, and installation processes. Finishes for stone abound (e.g. honed, polished, water-jet, brushed, flamed or thermal, antiqued, and tumbled); they allow designers and contractors to extend the life of the material, resist weathering, and improve performance, while also reducing waste, water, and resources during the process. (For example, computer numerically controlled [CNC] machinery can be used to apply a finish to stone with recycled water more precisely, and in less time, than with traditional hand methods.)
Using multiple finishes on one stone can also create completely different looks or serve different purposes. For example, a high-polished finish on marble lobby walls creates a sense of style and brings out the richest and deepest colors of the stone. However, combining it with a thermal finish to achieve slip-resistance on the flooring will meet accessibility requirements. Talking with the quarrier, fabricator, and installer helps design/construction professionals understand how to select the best finish options for their particular project, saving time and resources along the way.
The new version of the U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design program, LEED v4, is beginning to move in the direction of life cycle assessments (LCAs), shining a brighter light on stone and its full potential and offering more options to explore when seeking LEED points.
An LCA is a process to assess the environmental impacts associated with all the stages of a product’s life from cradle to grave—that is, from raw material extraction through materials processing, manufacture, distribution, use, repair and maintenance, and disposal or recycling. Interpreting the results of an LCA helps designers and contractors make more informed decisions when selecting and specifying materials for green projects. Thus far, the natural stone industry has conducted lifecycle inventory studies for granite, limestone, sandstone, and slate. (These studies can be accessed through the Natural Stone Council’s website at naturalstonecouncil.org/education-training/stone-sustainability. They can be utilized for green building project data and documentation.)
Major corporations all over the world are undertaking LCAs in-house or commissioning studies, while governments support the development of national databases to support LCA. There is growing use of LCA for ISO Type III labels called environmental product declarations (EPDs), which are defined as “quantified environmental data for a product with pre-set categories of parameters based on the ISO 14040 series of standards, but not excluding additional environmental information.”
Third-party-certified LCA-based labels provide an increasingly important basis for assessing the relative environmental merits of competing products. Third-party certification plays a major role in today’s green building industry. Independent certification can show a company’s dedication to safer and environmentally friendly products to customers, clients, and building owners.
Aside from LCAs, EPDs, and the related material ingredient reporting, the main areas of change within LEED v4 are:
Each of these aspects can have an impact on the selection, sourcing, and applications of stone. Understanding the associated challenges, the Natural Stone Council (NSC) has created sustainability standards for natural dimension stone. The American National Standards Institute/Natural Stone Council (ANSI/NSC) 373, Sustainable Production of Natural Dimension Stone, along with NSC’s chain-of-custody (COC) standard, helps designers identify stones in the marketplace that have been quarried and processed or fabricated at the highest levels of practice.
ANSI/NSC 373 sustainability assessment
ANSI/NSC 373 establishes criteria for the natural stone industry to measure the extent to which natural stone is produced sustainably. Developed by the Natural Stone Council in association with NSF through the National Center for Sustainability Standards (NCSS), the standard establishes a set of well-defined environmental, ecological, social responsibility, and human health requirements for stone quarries and processors.
With the development of NSC 373, facility operators can apply the standard to quarry operations, stone fabrication, or both for full certification. Businesses can also consider COC compliance through their entire supply chain. If a company is engaged in both quarrying and stone fabricating, it can elect to certify either the quarry or fabrication operations, or both, but each will be evaluated separately for conformance to the standard. By achieving certification to NSC 373, quarries and processors can meet green building industry demands for more sustainably produced stone products. (For more information on the NSC 373 standard or certification, e-mail email@example.com or visit NSC’s website at www.naturalstonecouncil.org/education-training/nsc-initiatives/dimensional-stone-standard.)
For example, a quarrier must take inventory of its water use, earning additional points toward the NSC 373 certification by demonstrating it is also capturing and recycling water in quarrying or processing operations. The quarrier can also earn points by reducing energy use onsite, as well as implementing renewable energy sources.
Across the building products spectrum, many architectural firms, owners, and contractors understand the importance of sustainability standards. In the broader sense, certification for stone provides that industry with a competitive edge when competing for green building projects and helps designers select the material that best serves the project.
The International Living Future Institute has already approved the use of the ANSI/NSC 373 in its Living Building Challenge Version 3.1 program within the “Material” petal under “Responsible Industry.” Project teams must advocate to quarries and/or manufacturers of all dimension stone products used within the project for certification under the NSC/373 standard.
Sustainable characteristics of stone (and LEED points to consider)
Stone can also contribute to LEED points in several different credits including Sustainable Sites (SS), Energy and Atmosphere (EA), Materials and Resources (MR), Integrative Process (IP), and Innovation (IN). Testing and documentation are required as part of the certification process.
One should explore the use of stone early in the design process to ensure the material’s role in high-performance design is understood and valued by all team members. This also allows time for any required testing or documentation to be requested and submitted to earn those valuable points.
For SS Credit 5, Heat Island Reduction (Option 1: Non-roof Measures), light-colored natural stone, with the required solar-reflective index (SRI), can be used on such features as landscaping walls, stair treads, and pavement. (This is done per ASTM E1980, Standard Practice for Calculating Solar Reflectance Index of Horizontal and Low-sloped Opaque Surfaces.) If the SRI test has not already be done by a fabricator or stone supplier, designers may request it to determine whether the stone they are interested in using on a project would qualify.
Energy and Atmosphere
Stone can play a role in achieving EA Credit 2, Optimize Energy Performance (Option 1: Whole-building energy simulation and Option 2: Prescriptive compliance). The material has the ability to store heat and slowly release it. This inherent thermal mass property has a positive impact on indoor ambient air temperature and, as a result, energy efficiency.
Materials and Resources
Due to the durability, recyclability, and regional availability of stone, the material’s use can potentially contribute to the earning of several credits in the Materials and Resources category. They include:
Applying the integrative process to a project where stone supports the reduction of energy and water use may be an option for IP Credit 1, Energy-related Systems and Water-related Systems.
Use of natural stone may contribute to exceptional performance in areas such as life cycle cost and durability, mold resistance, and improved indoor air quality (IAQ).
Seeking multiple solutions and benefits using stone
High-performance buildings are often expected to last 50 to 100 years (or longer), remaining aesthetically pleasing over time. Natural stone has long been chosen for its wide range of aesthetics due to color, pattern, grain, texture, and other natural variations. With new options for fabricating and finishing, and new stone choices in the marketplace, the visual options have been greatly expanded; they can be applied to any type of project of any scope, scale, or location.
Stone improves overs time and its aged patina resonates with aesthetic values that have no expiration. However, a client or designer’s aesthetic values can also have an impact on the environmental aspects of a project. For instance, if only a portion of a stone block’s grain, texture, or color is considered desirable, the remaining stone can end up as waste. By finding creative uses for that remaining material, or expanding the aesthetic range of the stone that is acceptable for the project, waste can be reduced or even eliminated.
Stone does not off-gas and is mold-resistant, contributing to IAQ levels for healthy, productive environments. In many cases, natural stone can be sourced or found locally, reducing carbon emissions from transporting materials from greater distances. It is important to weigh the decision to use local materials over the long term. Research has shown the largest impacts during the life cycle of stone do not occur during the transportation stage, but during the processing stage (Figure 1). If the design life of the building is 75 to 100 years, then the transportation impacts only occur once during that period, compared to a material needing replacement every seven to 10 years.
Stone can also be reused or recycled, minimizing the need for raw or virgin materials and reducing material replacement costs over a longer period. Mark Biedron, the founder of The Willow School (Gladstone, New Jersey) understood this concept well. The project’s team chose to incorporate several sources of local, recycled stone into the school to achieve LEED credits while also establishing a 150-year life cycle for the building. The classrooms used the remains of two barns and a house from Eastern Pennsylvania dating to the 19th century—a 75 percent hand-cut limestone and 25 percent sandstone mixture. This stone had already served for 100 years in the barns, but was expected to last another 150 in the school—a testimony to the material’s endurance.
The project requirements also stipulated the following:
The design called for the stone to be used as part of the façade and cavity walls in 200-mm (8-in.) sizes. At the foundation, the stone was specified at 100 mm (4 in.) and had to be solidly mortared to the foundation. The stone was also used for the lintels. All these approaches supported the goals of meeting the 150-year life cycle with durable materials and installations. Due to the unique nature of the project, the stone detailing had to be specified onsite.
A different approach to sustainability and performance was taken by architect David Hughes for the creation of a train drivers’ facility in Ireland. The project was designed to meet Passivhaus requirements, which attempt to strike a balance between the heat losses (e.g. through the building fabric and ventilation) with the heat gains (e.g. from people, appliances, lighting, and solar gains in the winter). The project was also designed for deconstruction in mind.
Granite was selected to address both goals, and can be used in another application in the future. This was achieved by designing the stone units to be the same size, except at the corners and details to windows, which made the ordering and processing of the stone more efficient. This also makes the stone’s reuse much easier due to the consistent dimension. The stone is dry-mounted on a stainless steel hanging system that uses the dead weight of the units (and some concealed dowels) to fix the stone on an independent self-supporting fixing system.
No silicone sealant was used in the joints for several reasons. First, from a deconstruction point of view, the material remains close to pristine. Technically, the joints allow for the pressure equalization of the ventilated air layer behind the stone. Aesthetically, omitting silicone avoids staining the edge of the stone, which can often be seen when silicone is used to seal the stone joints.
With many light-colored stones available, landscape design or site elements are enhanced by including stone as paving, stairs, railings, and walls to reduce the absorption, retention, and emittance of solar heat, contributing to reductions in heat island effect. Understanding the thermal properties of natural stone will encourage designers to incorporate it into the building envelope design for energy reduction strategies. Maintenance costs of natural stone are also minimal, contributing to reduced operations and maintenance costs over time. However, coordination with the operations and maintenance crews is essential to ensure sustainable cleaning methods are implemented.
Use of the most appropriate treatment and cleaning products is important to extend the life of the stone. Strong acidic cleaners can destroy stone, especially limestone and sandstone. If joint sealants are utilized, they need to be replaced every 10 to 15 years, depending on the type of sealant. If mortar is used, tuckpointing may be required during the life of the cladding.
There are many different approaches to creating a high-performance building project using natural stone. By understanding the drivers in the sustainability and high-performance building movement, including advancements in the natural stone industry, one will be equipped with the knowledge of how to select, source, and install the best stone for the project. This leads to a building that performs well and makes an excellent ROI over a long period.
Stephanie Vierra, Assoc. AIA, LEED AP BD+C, is the president of Vierra Design & Education Services LLC. With almost 30 years of experience in architectural associations, practice, and research, she has developed, managed, and taught programs that support an interdisciplinary and integrated approach to a variety of design and technical topics. Vierra has actively developed education and outreach programs on sustainability for the natural stone industry for the last decade, teaching and writing extensively on the material. She served on the NSC 373 green standard and Chain of Custody standard committees for the natural stone industry, and is a technical editor for the National Institute of Building Sciences (NIBS) Whole Building Design Guide (WBDG) portal. Vierra can be reached at firstname.lastname@example.org.
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