Cast Stone and the LEED® Certification Program
The U.S. Green Building Council (USGBC) developed the LEED rating system; LEED stands for Leadership in Energy and Environmental Design. A separate entity, the Green Building Certification Institute (GBCI) administers LEED project certification and professional credentialing programs. The LEED certification program was developed to provide a method to define and measure what are commonly called “green buildings”. From its inception as a pilot program for new buildings in 1998 to the present, the LEED certification program has expanded and grown dramatically. There are numerous LEED rating systems under development or in use corresponding to different types of construction, including Existing Buildings Operations & Maintenance, Commercial Interiors, Homes, Schools, and others. The most widely used rating system in the U.S. is currently LEED® for New Construction ∓ Major Renovations™ (LEED for New Construction). While each rating system is distinct, most of the topics covered can be grouped into the same general categories. This Bulletin examines the requirements of LEED for New Construction 2009 (LEED v.3) and its relevance to cast stone.
The Use of Cast Stone
The LEED® rating system
Figure 1: LEED for New Construction 2009 point distribution
Figure 2: LEED for New Construction 2009 certification levels
Earning LEED Points
Sustainable Sites (SS)
SS Credit 2 - Development Density (1 pt) – the intent of this credit is to encourage development in urban areas with existing infrastructure. Masonry materials are often used for urban infill development because of their appearance, size and scale, fire ratings, as well as for benefits in space required for construction. Cast stone masonry can often be installed without the use of a crane, thus helping to minimize the need for large equipment on site.
SS Credit 5.2 – Maximize Open Space (1pt) – the intent of this credit is to reduce the development footprint, including hardscape, parking, roads, etc. associated with the site. By building with materials such as cast stone, which do not require large open areas around the building perimeter during construction, the development footprint can be kept to a minimum and much of the surrounding land left undisturbed.
SS Credit 7.1 – Non-Roof Heat Island (1 pt)– the intent of this credit is to reduce the retention of heat due to dark colored surfaces by providing shade, using open grid pavement or using hardscape materials that have a solar reflectance index (SRI) of at least 29 for a minimum of 50% of the sites hardscape. Using cast stone hardscape as caps on landscaping walls, stair treads, and pavers that are light in color is one option for earning this point. New cast stone made with ordinary Portland cement has an SRI around 35. New cast stone made with white Portland cement generally has an SRI of 86.
SS Credit 7.2 – Roof Heat Island (1 pt) – the intent of this credit is the same as for Credit 7.1, but addresses roofs. This credit can be earned by utilizing reflective roofing materials for at least 75% of the roof’s surface or installing a vegetated roof over at least 50% of the roof or some combination of both. Cast stone pavers can provide access via a walking surface as part of a vegetated, solar or other roof, or they can be used on their own. Non-vegetated roofs with slopes equal to or less than 2:12 must have an SRI rating of 78 while roofs with slopes of greater than 2:12 must have an SRI of at least 29.
Energy & Atmosphere (EA)
EA Prerequisite 2 – minimum energy performance (0 pt) – as part of a masonry wall, cast stone can mitigate temperature swings and help achieve the require energy performance particularly when interior masonry is left exposed.
EA Credit 1 - Optimize energy performance (up to 19 pts) – as part of a masonry wall, cast stone can be used to help reduce the amount of energy consumed by the building. The benefit of thermal mass is best recognized when using an energy modeling tools such as BLAST or EnergyPlus.
Materials & Resources (MR)
MR Credit 1.1– Building Reuse – Maintain Existing Walls, and Roof (up to 3 pts) – Credit 1.2 – Building Reuse – Maintain Existing Interior Nonstructural Elements (1 pt) – The intent of these credits is to encourage the renovation and reuse of existing buildings and interiors. Credit 1.1 covers the reuse of a building’s structure and façade. Masonry buildings, many of which incorporate cast stone details, are good candidates for reuse. In addition, cast stone features on the building interior such as columns, fireplace mantels and surrounds, stair treads, etc. are good candidates for reuse as part of Credit 1.2.
MR Credits 2.1 and 2.2 – Construction Waste Management (1pt each) – The intent of these credits is to eliminate construction waste from landfills. Up to two points can be earned for recycling or salvaging specified amounts of construction waste. On-site waste from cast stone elements is limited primarily to packaging materials. Cast stone elements are carefully detailed and exact amounts are delivered to the site so that waste stone is nearly eliminated. However, this credit is not presently structured to account for materials that do not have any or little on-site waste. It may be possible to meet the intent of this credit or an Innovation and Design credit for utilizing materials such as cast stone that have little on-site waste. The use of Innovation and Design credits are discussed later in this Bulletin. Any waste cast stone elements that are present can be crushed and used as aggregate or fill.
MR Credits 3.1 and 3.2 – Materials Reuse (up to 2 pt) – These credits award points for the use of salvaged materials at a specified amount. Salvaged cast stone elements can be reused to help earn this credit. Anchoring details that allow for disassembly can facilitate this. Larger elements not set in mortar are especially suited for salvaging. In addition, cast stone can be repaired to conceal damage that may occur during disassembly and removal.
MR Credits 4.1 and 4.2 – Recycled Content (up to 2 pt) – Points can be earned if the value of the recycled content of materials on a project is a least 10% for one point or 20% for two points. The recycled content of all building materials on the project must be determined to earn this credit. Cast stone elements can help earn this credit when they incorporate recycled materials into their mix, most often as aggregates or supplementary cementitious materials. Pre-consumer (post-industrial) recycled materials that may be incorporated into cast stone include recycled aggregate, or slag that can be used as an aggregate, and supplementary cementitious materials like fly ash. Color may be affected by incorporation of certain recycled materials, so contacting the cast stone manufacturer is recommended. (You may want to point out that you only get ½ the % for pre-consumer recycled content vs. post consumer.)
MR Credits 5.1 and 5.2 – Regional Materials (up to 2 pt) – The intent of these credits is to encourage use of materials that are extracted and manufactured within a region. One point is awarded if 10% of the total value of construction materials comes from regional sources and two points if that value is 20%. Raw materials used in the manufacture of cast stone include the constituent materials such as cement, aggregate and water; wood, fiberglass, rubber and other materials used for forms; and steel, plastic and foam packaging materials. Most cast stone is locally produced and many raw materials are extracted or harvested within 500 miles of a project site. Exceptions to this may be cement and other materials used in the molding or packaging process.
Indoor Environmental Quality (IEQ)
IEQ Credit 4 – Low-Emitting Materials (up to 4 pt) – IEQ Credit 4 covers emissions from four subcategories of Low-Emitting Materials; Adhesives and Sealants, Paints and Coatings, Flooring Systems and Composite Wood and Agrifiber Products. Each subcategory is worth one point. While all of these subcategories are structured to keep the measured amount of VOCs of a building product below a specified limit using industry standards for measurement and specification, the intent of each is to reduce the amount of VOCs in the building interior. In this way, cast stone, like other masonry materials that do not contain any VOCs, meets the intent of eliminating VOC’s from the indoor environment when used on exposed interior walls or floors.
Innovation & Design Process (IDP)
Designers utilizing the LEED for New Construction rating system are encouraged to look for opportunities and the synergy that can occur when cast stone is chosen for use on a project.
1 Certified wood is the only product that can earn 1 point through its use under Materials & Resources Credit 7.
Ms. Subasic has been a member of The Masonry Society (TMS) since 1992 and a member of the Board of Directors since 2002. She serves on the Architectural Practices committee, the Design Practices committee, and is a founding member of the Sustainability Committee. Ms. Subasic also represents TMS on the U.S. Green Building Council and is a member of the Green Globes ANSI Standard Development Committee.
This Technical Bulletin is provided by the Cast Stone Institute®, and is intended for guidance only. Specific details should be obtained from the manufacturer or supplier of the Cast Stone units.