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Concrete Masonry & Hardscape Products in LEED® 2009

  • August 2018

INTRODUCTION

Concrete masonry can make a significant contribution to meeting LEED Green Building certification. Leadership in Energy and Environmental Design (LEED) is a voluntary rating system developed by the United States Green Building Council (USGBC) to evaluate a building’s environmental impact and performance. LEED provides design guidelines and third-party certification for defining what constitutes a “green” building. LEED’s overall goals are to improve: occupant well-being, the environmental impacts and the economic return of new buildings. USGBC offers several green building certification programs, each tailored to a specific market or application.

LEED version 2.2 will remain in effect until LEED 2009 is completed, around September 2009. Once LEED 2009 is active, version 2.2 registered projects can continue to certification as version 2.2 projects. This TEK provides details on LEED for New Construction & Major Renovations 2009 (LEED NC 2009) (ref. 1).

The USGBC has incorporated several changes into LEED 2009. These major changes are:

  • Prerequisite and credit harmonization across rating systems (LEED Bookshelf). The intents and requirements for common prerequisites and credits among the various rating systems (i.e., New Construction, Schools, Retail, etc.) have been standardized to minimize differences or contradictions between rating systems. There are still unique prerequisites and credits in each rating system. In addition to harmonization, credit interpretation requests (CIR) that have set precedents or shown a need for clarification have been incorporated.
  • A set schedule for updating the rating systems is being established, similar to building code development schedules.
  • The quantity and distribution among the categories of points was changed to better reduce or improve a buildings environmental impact. These changes are most readily seen in the increase in the total number of points and in the allocation of points in each category. One of the major tools for weighting the categories was TRACI (Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts), established by the EPA.
  • The new Regional Priority category provides an opportunity for a project to achieve credit for addressing regional environmental concerns. The details on this category are still being finalized as the USGBC councils and chapters assemble and submit their requests to the USGBC.

LEED NC 2009 is comprised of seven categories each with its own prerequisites and credits. The prerequisites in all categories must be met to earn LEED certification. Using concrete masonry and concrete hardscape products can contribute to certification in the following LEED categories: Sustainable Sites, Energy & Atmosphere, Materials & Resources, Innovation and Design, and possibly Regional Priority*.

POINTS FOR CERTIFICATION

LEED NC 2009 provides a checklist of mandatory prerequisites as well as voluntary credits in seven basic categories: Sustainable Sites, Water Efficiency, Energy and Atmosphere, Materials and Resources, Indoor Environmental Quality, Innovation and Design Process, and Regional Priority Credits. Projects earn one or more credits by meeting or exceeding a checklist item’s technical requirements. Figure 1 illustrates the categories where concrete masonry products can contribute.

Points for voluntary credits add up to a final score which can earn the building one of four possible levels of certification. As shown in Figure 1, concrete masonry and hardscape products can make a significant contribution to LEED certification. A project must earn at least 40 points for LEED certification. Silver (50 pts), gold (60 pts), and platinum (80 pts) certification levels are also available. There are a total of 110 points available from the seven credit categories.

EARNING LEED POINTS

The following sections briefly describe how concrete masonry and hardscape products can contribute to earning points in each of the LEED credit categories.

Sustainable Site Prerequisite—Construction Activity Pollution Prevention

Reducing pollution due to construction activity is a prerequisite. Pollution includes soil erosion, waterway sedimentation and dust. Articulated concrete block (ACB) and open grid pavers can be used for soil erosion control and dust control. See References 3 and 4 for more information.

Sustainable Site Credit—Development Density

Developing an urban lot in lieu of an undeveloped “greenfield” area can earn a project one point towards certification. Concrete masonry and retaining walls enable designs that take advantage of small, irregularly shaped lots, where access and open area are often at a premium. Concrete masonry, because of its relatively small modular size does not require large equipment for delivery or placement, nor are large staging areas required for construction.

Sustainable Site Credit—Site Development

The overall goal of this credit is to preserve or restore natural habitats and to promote biodiversity. There are two parts to this credit, Protect or Restore Habitat and Maximize Open Space, each worth one LEED point.

On greenfield sites, segmental retaining walls and/or cantilever retaining walls can be used to limit cut and fill requirements. Reducing cut and fill operations preserves habitat and limits the disturbed area.

A second point can be earned by exceeding the local zoning requirement for open space by 25%. This 25% threshold can be met by reducing the site disturbance or by creating vegetated open space (the credit also provides requirements for projects where no local zoning requirement exists). Once again, retaining walls can limit site disturbance by reducing the amount of slope alteration.

For urban projects earning the Development Density credit, pedestrian hardscape areas, such as those provided by concrete pavers, can be counted as open space, although only 25% of the open space can be hardscape. Wetlands and ponds may count as open space if the side slope ratio does not exceed 1:4 and are vegetated. Articulated concrete block is well suited to wetland and pond construction.

Sustainable Site Credit—Stormwater Management

The intent of this credit is to limit disruption of natural hydrology by reducing stormwater runoff quantity and by improving the quality of stormwater runoff, through methods such as reducing impervious cover, increasing on-site infiltration, and managing stormwater runoff. One of the LEED-suggested strategies is to use permeable paving that promotes infiltration.

The requirement for controlling stormwater rate and quality is implemented either by limiting the post-development peak discharge rate or by implementing a plan that protects the receiving streams from excessive erosion.

An additional point may be earned by implementing Best Management Practices to capture and treat at least 90% of the average annual rainfall and removing 80% of the post development suspended solids.

Pavements are major contributors to stormwater runoff, and permeable pavements that directly pass water from the pavement surfaces to the underlying soil can help alleviate runoff. Benefits of permeable pavements include reduced stormwater runoff, direct recharge of underlying groundwater systems, partial treatment of pollutants in the runoff and increased usable space. Both permeable pavers and open-cell pavers (also known as turf stone or grid pavers) offer the option of replacing impermeable pavement with permeable pavement. These pavers can help earn one point each for reducing stormwater runoff and for treatment of stormwater. References 4, 5, and 6 provide more detailed design information for these pavements.

For the protection of receiving stream channels, ACB products can effectively reduce soil erosion and allow for a protected and
vegetated area.

Sustainable Site Credit—Heat Island Effect, Non-Roof

Urban heat islands are localized areas of high temperature, caused by the retention of solar energy on constructed dark surfaces. The effect is elevated temperatures in urban areas and a greater energy demand for cooling.

LEED offers one credit point for non-roof heat island reduction on projects if 50% or more of the site hardscape (including roads, sidewalks, courtyards and parking lots) are either shaded or use paving materials with Solar Reflectance Index of at least 29. Typical values for SRI are 35 for new gray concrete and 19 for weathered (unclean) concrete.

The SRI requirement can be met either by using light-colored concrete pavers in lieu of asphalt; or by using open-cell pavers, which can support grass or other plant materials in the pavers’ open grid areas. The open cell pavers must be considered at least 50% pervious.

Energy & Atmosphere Prerequisite—Minimum Energy Performance

This prerequisite requires a 10% improvement (for new construction) or a 5% improvement (for major renovations) over the ASHRAE 90.1 2007, Appendix G, Building Performance Rating Method (ref. 7). There are two other options for meeting this prerequisite: using the ASHRAE Advanced Energy Design Guide appropriate to the building type; and using the Advanced Buildings Core Performance Guide by the New Buildings Institute (NBI) (refs. 8, 9). These publications are prescriptive design guides that have specific building size and usage criteria.

The intent of these credits is to improve energy efficiency beyond ASHRAE 90.1-2007. Energy savings attributable to thermal mass inherent in concrete masonry construction contribute to this goal when used in conjunction with passive solar heating and/or ventilation cooling. Because concrete masonry has high thermal mass and specific heat, it provides very effective thermal storage. Masonry walls remain warm or cool long after the heat or air-conditioning has shut off. This, in turn, can effectively: reduce heating and cooling loads; improve occupant comfort by moderating indoor temperature swings; and shift peak heating and cooling loads to off-peak hours.

Using ASHRAE/IESNA Standard 90.1 Appendix G, Performance Rating Method, entails using a comprehensive, whole-building analysis software simulation program, capable of projecting the building’s energy consumption and associated costs based on an hour-by-hour simulation of a full year of weather data. Examples of such programs include DOE-2 and BLAST. These programs can accurately model concrete masonry’s thermal mass and predict the associated energy savings. These energy simulations have been used to demonstrate in many cases that, with all other variables kept the same, a high mass concrete masonry building can be heated and cooled using less energy than a similar frame building. See References 7 and 10 for more information.

Energy & Atmosphere Credit—Optimize Energy Performance

As many as 19 points can be achieved under this credit by incrementally increasing the energy efficiency of the building by 12 44% for new construction using Appendix G of ASHRAE 90.1-2007. One point is awarded for each 2% improvement. The Advanced Energy Design Guide and the Advanced Buildings Core Performance Guide can be used to achieve this credit. However, using these guides limits the potential points earned to 3.

Note that for the purposes of this credit, savings attributable to the building thermal envelope are cumulative, and so are added to savings from high efficiency HVAC, heat recovery equipment, daylighting, etc. Thus, all incremental improvements contribute toward project certification.

Materials & Resources Credit—Building Reuse

The building reuse credit is intended to extend the life of the existing building stock, thereby conserving resources, reducing waste and reducing the environmental impacts of new construction. Credits are earned when developers maintain the majority of an existing building’s structure and envelope. The building envelope is the exterior skin and framing excluding window assemblies and non structural roofing.

This credit is often obtainable when renovating buildings with exterior concrete masonry walls, because concrete masonry is an exceptionally durable material with a life cycle measurably longer than many other building envelope products. Concrete masonry construction provides the opportunity to refurbish the building should the building use or function change, rather than tearing down and starting anew.

Three points are available under this credit. These points are awarded based on the percentage of building reused. One point is awarded for 55% reuse, 2 points for 75% reuse, and 3 points for 95% reuse. An additional point is available if at least 50% of the interior, non-structural items remain. The percentages are based on the area of the completed building (existing and additions).

Materials & Resources Credit—Construction Waste Management

This item encourages contractors to divert demolition and landclearing debris from landfills and incinerators.

The construction waste management credit is awarded based on recycling or salvaging at least 50% of construction waste, based on either weight or volume. Because concrete masonry is a relatively heavy construction material and can be recycled into aggregate for road bases or other concrete products, pipe bedding or construction fill, this credit is obtainable either when buildings with concrete masonry are demolished or, in new construction when saw-cut scraps and broken pieces of concrete masonry are crushed and reused. In addition, intact and unused concrete masonry units can be redirected to other projects or donated to charitable organizations such as Habitat for Humanity.

This credit is worth 1 point if 50% of the construction, demolition and land clearing waste is recycled or salvaged and 2 points for 75%.

Materials & Resources Credit—Materials Reuse

This checklist item encourages the reuse of salvaged materials on the project, such as crushed concrete masonry, and it awards one point if the value of all reused materials is at least 5% of the total value of materials on the project. Two points are awarded at the 10% threshold. Note that the same materials cannot be claimed for both the construction waste management credit, above, and the materials reuse credit on the same project.

Materials & Resources Credit—Recycled Content

The use of building products with recycled content can earn the project one or two points. To earn the point(s), the project must meet the threshold percentage (10% for 1 point; 20% for 2 points) based on the total of all building materials used in the project.

Concrete masonry can potentially incorporate recycled materials, with due consideration to ensure that the use of these materials does not adversely affect the quality of the masonry units or construction. Recycled materials can be used as a partial replacement for cement, or as aggregate.

A full discussion, including calculation methods for recycled content, is discussed in TEK 06-06B, Determining the Recycled Content of Concrete Masonry Products (ref. 11).

Materials & Resources Credit—Regional Materials

Using materials and products that are locally extracted and manufactured supports the use of indigenous resources and reduces environmental impacts of transportation. Concrete masonry materials are most commonly extracted and manufactured close to the jobsite, thus helping to fulfill this LEED credit.

The LEED requirement is to “specify that a minimum of 10% of building materials be extracted, processed & manufactured within a radius of 500 miles.” Concrete masonry usually qualifies, since block plants are often within 50 mi (80 km) of a job site. The percentage of materials is calculated on a cost basis. If only a fraction of a product or material is extracted/harvested/recovered and manufactured within the region, then only that percentage (by weight) contributes to the regional value.

Innovation and Design Process

The intent of this item is to provide design teams with an incentive to go beyond the LEED requirements and/or to award points for innovative strategies not specifically addressed in the LEED rating system. Examples that may qualify are: substantially exceeding the building energy performance criteria (Energy & Atmosphere Credit 1), or including characteristics not directly referenced by LEED, such as acoustic performance and life cycle analysis of materials used.

Potential strategies for achieving Innovation & Design points with concrete masonry and hardscape products include:

  • Show concrete masonry’s advantage in life cycle environmental impact over other building materials such as steel and aluminum due to its durability, low maintenance, and low embodied energy.
  • Address indoor air quality issues, by eliminating the need for paints with exposed concrete masonry walls, thereby reducing the potential for VOC (volatile organic compounds) emissions.
  • Improve indoor air quality using concrete masonry due to the reduced potential for mold growth ( concrete masonry is not a food source food for mold) and concrete masonry’s ability to be cleaned instead of being replaced in the event of a mold incident.
  • Show concrete masonry’s material usage efficiency by incorporating partial grouting and prestressed masonry design techniques.
  • Demonstrate concrete masonry’s intrinsic acoustical characteristics. See Reference 12 for further information.
  • Make a case for concrete masonry’s superior fire resistance and fire containment qualities. See Reference 13 for further information.

Regional Priority

These credits provide a means for addressing local environmental priorities. There are six credits, but no more than four can be earned per project. These credits will pertain only to certain geographic locals, and the projects must be located within the relevant region to be eligible. Details on these credits will be available on the USGBC web site, www.usgbc.com.

REFERENCES

  1. LEED 2009 New Construction for Member Ballot. U.S. Green Building Council, 2008.
  2. LEED-NC for New Construction v2.2 Reference Guide. First Edition, U. S. Green Building Council, October 2005.
  3. Articulated Concrete Block for Erosion Control, ACB-TEC-001-14 Concrete Masonry & Hardscapes Association, 2014.
  4. Construction of Permeable Interlocking Concrete Pavement Systems, PAV-TEC-018-22, Concrete Masonry & Hardscapes Association, 2022.
  5. Concrete Grid Pavements, PAV-TEC-008-21, Concrete Masonry & Hardscapes Association, 2021.
  6. Achieving LEED Credits with Segmental Concrete Pavements, PAV-TEC-016-016, Concrete Masonry & Hardscapes Association, 2016.
  7. Energy Standard for Buildings Except Low-Rise Residential Buildings, ANSI/ASHRAE/IESNA Standard 90.1-2007. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 2007.
  8. Advanced Energy Design Guides. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. Available for free download from: http://www.ashrae.org/technology/page/938.
  9. Advanced Buildings Core Performance Guide. New Buildings Institute, 2007.
  10. Standard 90.1-2007 User’s Manual. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 2008.
  11. Determining the Recycled Content of Concrete Masonry Products, TEK 06-06B, Concrete Masonry & Hardscapes Association, 2009.
  12. Sound Transmission Class Rating for Concrete Masonry Walls, TEK 13-01D Concrete Masonry & Hardscapes Association, 2012.
  13. Fire Resistance Rating of Concrete Masonry Assemblies, TEK 07-01D Concrete Masonry & Hardscapes Association, 2018.

Determining the Recycled Content of Concrete Masonry Products

  • August 2018

INTRODUCTION

Sustainable development has been defined as development that meets the needs of the present without compromising the ability of future generations to meet their own needs (ref.1). This is often expressed as a holistic approach to building design, with the goal of optimizing environmental, economic and social impacts, from site selection through building operation and maintenance. A sustainable building optimizes resource management and operational performance, while minimizing risks to human health and the environment. As such, providing a sustainable building project encompasses far-reaching design decisions, and recognizes the interrelationships between virtually all elements and phases of the project.

A range of products and programs has been developed to help designers achieve a more sustainable built environment. Whether in the form of design guidelines for particular building types, or rating systems that step the design team through a series of design considerations, all aim to provide practical guidance for achieving the almost overwhelming goal of sustainability.

Referenced and in some cases mandated by some branches of the Federal government, as well as many state and local governments, the United States Green Building Council’s (USGBC) Leadership in Energy and Environmental Design (LEED®) has become perhaps the most widely used of these programs in recent years. LEED is a voluntary rating system designed to provide guidance as well as national third-party certification for defining what constitutes a “green” building.

Concrete masonry building and hardscape products can make a significant contribution to meeting LEED certification. This contribution is augmented by the recycled content potential of the companion products necessary for a concrete masonry wall, such as grout, mortar and reinforcement products.

Concrete masonry building and hardscape materials can contribute to earning credits in several LEED categories, including Sustainable Sites, Energy and Atmosphere, Materials and Resources and Innovation in Design. More detail on LEED strategies incorporating concrete masonry and hardscape materials is available in TEK 06 09C, Concrete Masonry and Hardscape Products in LEED 2009 and PAV-TEC-016-16, Achieving LEED Credits with Segmental Concrete Pavement (refs. 2, 3).

LEED includes specific rating systems for various applications. The information in this TEK is applicable to LEED for new construction, school, retail, and core and shell development (refs. 4-7).

For these LEED programs, Materials and Resources Credit 4: Recycled Content allows up to two LEED certification points for using materials with recycled content. The inert nature of concrete masonry lends itself well to incorporating recycled materials as cement replacements, as aggregates and as other constituents in the concrete mix. This TEK provides guidance on determining the recycled content of concrete masonry products for the purpose of earning LEED credit under the new construction, school, retail, and core and shell development LEED programs.

The LEED for Homes (ref. 8) recycled content credit differs from these other programs. Concrete masonry walls are eligible for recycled content credit under the LEED for Homes Materials and Resources Credit 2: Environmentally Preferable Products, provided the masonry contains at least 25% recycled content (post-consumer plus one-half pre-consumer, as described in the following sections). Note, however, that the National Association of Home Builders with the International Code Council has developed their own green building standard that has similar requirements (ref. 9). See www.nahbgreen.org for more information.

USE OF RECYCLED MATERIALS IN CONCRETE MASONRY AND HARDSCAPE UNITS

When concrete masonry products incorporate recycled materials, due consideration must be given to ensure that the use of these materials does not adversely affect the quality or safety of the units or construction. Note that some recycled materials may only be regionally available. Designers should work closely with concrete masonry manufacturers to substantiate recycled content.

Unit Specifications

Whether produced using recycled or virgin materials, concrete masonry products are required to meet the applicable ASTM unit specification (see Table 1). These standards contain minimum requirements that assure properties necessary for quality performance. For example, many concrete masonry units are required to conform to ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units (ref. 11). ASTM C90 requirements include material requirements for aggregates, cementitious materials, and other constituent materials, physical requirements, finish and appearance requirements, and permissible variations in dimensions.

Aggregates, including recycled aggregates, for concrete masonry units are required to meet ASTM C33, Standard Specification for Concrete Aggregates, or C331, Standard Specification for Lightweight Aggregates for Concrete Masonry Units (refs. 19, 20), except that grading requirements do not have to be met. Aggregate characteristics governed include limits on deleterious substances and aggregate soundness.

Cements are required to meet ASTM C150 and supplemental cementitious materials such as fly ash must meet ASTM C618 (refs. 27, 28). In addition to cementitious materials and aggregates, the ASTM unit specifications also allow for the inclusion of “Other Constituents,” such as pigments, integral water repellents and finely ground silica. For a material to qualify for inclusion in a concrete masonry product under this provision, the material:

  • must have been previously established as suitable for use in the product, and
  • must either conform to applicable ASTM standards or be shown, via test or experience, not to be detrimental to the durability of the units or other masonry materials.

Fire Resistance Ratings

For construction requiring a fire resistance rating, the use of recycled aggregates may impact the method used to determine the hourly rating, because concrete masonry fire resistance ratings vary with the aggregate type(s) used to manufacture the units. Concrete masonry fire ratings can be determined by: model building code prescriptive tables (ref. 21), a standard calculation method as provided in Section 721 of the International Building Code (IBC) (ref. 21) and the ACI/TMS 216 (ref. 22); testing in accordance with ASTM E 119, Standard Test Methods for Fire Tests of Building Construction and Materials (ref. 23); commercial listing services; and deemed-to comply assemblies included in some building codes. These tools also include ways to increase a wall system’s fire resistance rating through careful placement of additional materials.

Currently, the standard calculation procedure applies to the following aggregate types: expanded slag, pumice, expanded clay, expanded shale, expanded slate, limestone, cinders, aircooled slag, calcareous gravel, and siliceous gravel. When units are made with a combination of these aggregates, the fire rating is determined by interpolation (see ref. 23 for more detail). When aggregate types other than those listed above are used, the fire resistance rating is determined using a method other than the standard calculation procedure.

TEK 07-01D, Fire Resistance Rating of Concrete Masonry Assemblies (ref. 24) contains a detailed discussion of concrete masonry fire ratings. Additional considerations for recycled aggregates which are not listed in the standard calculation procedure are their stability, safety and load-carrying ability when subjected to fire.

LEED MATERIALS & RESOURCES CREDIT 4: RECYCLED CONTENT

By increasing the demand for products that incorporate recycled materials, the Recycled Content credits are intended to reduce the environmental and societal impacts associated with extracting and processing virgin materials.

LEED awards 1 point to projects that demonstrate that the total amount of a project’s recycled content exceeds 10% based on both weight and the total building product costs. An additional point is awarded if the recycled content reaches 20%. Also, if the recycled content reaches 30%, a third point can be earned as an Innovation & Design credit.

LEED refers to the International Organization for Standardization (ISO) for the definition of what constitutes recycled content, and for the basis of determining the percentage – i.e., weight (ref. 25). Recycled materials are those materials diverted from the solid waste stream, either during the manufacturing process (pre-consumer) or after their intended use (post-consumer). The recycled content for LEED credit is determined as the sum of all post-consumer recycled content plus one-half of the pre-consumer recycled content.

To claim this credit, the LEED NC Reference Guide suggests establishing a project goal for recycled content materials, and dentifying product suppliers who can achieve this goal. The following sections describe how concrete masonry and hardscape products can contribute to recycled content goals.

Pre-Consumer Recycled Content

Pre-consumer (post-industrial) content as defined by the LEED v2.2 reference manual is “material diverted from the waste stream during the manufacturing process. Excluded is reutilization of materials such as rework, regrind or scrap generated in a process and capable of being reclaimed within the same process that generated it (Source ISO 14021). Examples in the pre-consumer category include planer shavings, plytrim, sawdust, chips, bagasse, sunflower seed hulls, walnut shells, culls, trimmed materials, print overruns, over-issue publications, and obsolete inventories.” (refs. 4, 25) It is important for the producer to work with the material suppliers to determine which materials can be considered recycled and which cannot. It is important for the producer to have documentation from the material supplier stating that a material is considered recycled for the purposes of contributing to LEED certification.

Post-Consumer Recycled Content

Post-consumer recycled content is consumer waste that can no longer be used for its intended purpose. The official LEED definition of a post-consumer material is “material generated by households or by commercial, industrial and institutional facilities in their role as end users of the product which can no longer be used for its intended purpose. This includes returns of materials from the distribution chain (ref. 26). Examples of materials in this category include construction and demolition debris, materials collected through curbside and drop off recycling programs, broken pallets (if from a pallet refurbishing company, not a pallet-making company), discarded products (e.g. furniture, cabinetry and decking) and urban maintenance waste (leaves, grass clippings, tree trimmings, etc.) (refs. 4, 25).

As with pre-consumer materials, a producer should work with the material supplier to document that the materials being used are specifically documented as post-consumer recycled material for the purposes of contributing to LEED certification.

DETERMINING RECYCLED CONTENT

The LEED recycled content credit(s) is based on the recycled content percentages, based on the total value of all permanently installed materials on the project. Note that mechanical, electrical and plumbing components are excluded from this total, as are specialty items such as elevators. In determining the percentages of recycled content, the contribution from concrete masonry and hardscape products is added to the contribution from other building components.

The following sections describe the procedure for determining the recycled content of a particular product, then combining all such data to determine the overall recycled content percentage for the project. The percentages are based on both weight and cost, as described below.

For a Product

The producer is responsible for reporting the percentages of reconsumer and post-consumer recycled content for each product sold. If the producer supplies other products in addition to block such as reinforcement, mortar, etc., the producer should also document the recycled percentages in each of these products and report them to the contractor who purchased them.

The percentages are based on weight, as follows:

As an aid to the producer, CMHA has developed a simple spreadsheet to calculate these percentages (see Figure 1). Figure 1 illustrates the process of determining the weights of all constituent materials; determining the total weight; then determining the percent by weight of each recycled material. The total pre-consumer and post consumer percentages are simply the sum of the individual material percentages in each category.

Note that Figure 1 includes an alternate calculation, applicable to concrete products only. This alternate calculation is described below.

For a Product: Alternate Calculation per LEED for New Construction and Major Renovations

LEED for New Construction and Major Renovations, Version 2.2 and the LEED Reference Guide for Green Building Design and Construction, 2009 Edition (ref. 5, 26) provide an alternate method to calculate and report the recycled content for concrete products that use supplementary cementitious materials (SCMs), such as fly ash or ground blast furnace slag cement. This alternate method allows the recycled content calculation to be based on only the cementitious materials, rather than on all materials in the concrete mix. This alternate method helps offset the fact that the recycled content calculation is based on weight, and SCMs are typically very low in weight. For concrete mixes with SCMs as the only recycled content, this alternate method will result in a higher recycled content value than the conventional approach. For concrete mixes that incorporate both SCMs and other recycled materials, the manufacturer may want to evaluate the percent recycled content using both methods to determine which method yields the best result.

The basic calculation is the same as that described in the previous section, except:

  • when determining the percent post-consumer and percent pre consumer recycled content, divide by the total weight of the cementitious materials only, and
  • when determining the recycled content value, multiply the percent recycled content by the total value of the cementitious materials only.

Use of the alternative calculation method requires that the value of the cementitious materials be used in place of the total value of the product when the LEED project team determines the value of the recycled content. The producer would likely benefit from describing this value as a percentage of the value of the whole product and not as a monetary figure. When requested, the producer should report this value to the direct customer and not to a third party.

For the Project as a Whole

Based on information from the product suppliers, the design team determines the recycled content value for the project as a whole as follows:

  1. For each product, the percent recycled content is determined as the percent post-consumer (reported by the supplier) plus one-half of the percent pre-consumer. For the example in Figure 1, the percent recycled content for the concrete masonry units is 17.9% + 1/2(37.1%) = 36.5%
  2. For each product, the recycled content value is determined as the percent recycled content multiplied by the total product cost for the project. For the hypothetical project referenced in Figure 1, if the total cost of the concrete masonry units is $90,000, the recycled content value of the concrete masonry units is 0.365($90,000) = $32,805. It is important to note that the cost used in this calculation is the amount paid to the producer or the contractor for the product. It is not the cost of the individual materials that constitute the concrete masonry or hardscape product. The product cost should be supplied by the contractor. It is the contractor’s responsibility to separate their labor charges from the material charges.
  3. For the project as a whole, the recycled content percentage is determined as the sum of the recycled content values of each product, divided by the total cost of all of these products. If this total recycled content percentage is 10% or higher, the project earns one LEED point; if it is 20% or higher the project earns two LEED points. Projects with recycled content percentages of 30% or more may be eligible for an additional Innovation in Design point.

CONCRETE MASONRY UNITS RETURNED FROM A JOB SITE

Unused concrete masonry units returned to the manufacturer from a job site are considered under Materials and Resources Credit 2: Construction Waste Management. Under Credit 2, the building project with unused materials can earn LEED point(s) for returning those materials, and hence diverting them from a landfill. If subsequently used on another project, the recycled content of the units as manufactured is reported to the contractor or design team, as for unused concrete masonry products.

REFERENCES

  1. Standard Terminology for Sustainability Relative to the Performance of Buildings, ASTM E2114-06a. ASTM International, Inc., 2006.
  2. Concrete Masonry and Hardscape Products in LEED 2009, TEK 06-09C, Concrete Masonry & Hardscapes Association, 2009.
  3. Achieving LEED Credits with Segmental Concrete Pavement, PAV TEC-016-16, Concrete Masonry & Hardscapes Association, 2016.
  4. LEED for New Construction and Major Renovations, Version 2.2, 3rd ed. U. S. Green Building Council, 2005.
  5. LEED for Schools for New Construction and Major Renovations, Version 2007. U. S. Green Building Council, 2007.
  6. LEED for Retail: New Construction and Major Renovations, Version 3. U. S. Green Building Council, 2008.
  7. LEED Green Building Rating System for Core and Shell Development, Version 2.0. U. S. Green Building Council, 2006.
  8. LEED for Homes Rating System. U. S. Green Building Council, 2008.
  9. NAHB Model Green Home Building Guidelines. National Association of Home Builders, 2006.
  10. Standard Specification for Concrete Brick, ASTM C55-06e1. ASTM International, 2006.
  11. Standard Specification for Loadbearing Concrete Masonry Units, ASTM C90-06b. ASTM International, Inc., 2006.
  12. Standard Specification for Nonloadbearing Concrete Masonry Units, ASTM C129-06. ASTM International, 2006.
  13. Standard Specification for Prefaced Concrete and Calcium Silicate Masonry Units, ASTM C744-05. ASTM International, 2005.
  14. Standard Specification for Concrete Facing Brick, ASTM C1634-06. ASTM International, 2006.
  15. Standard Specification for Solid Concrete Interlocking Paving Units, ASTM C936-08. ASTM International, 2008.
  16. Standard Specification for Concrete Grid Paving Units, ASTM C1319-01(2006). ASTM International, 2006.
  17. Standard Specification for Dry-Cast Segmental Retaining Wall Units, ASTM C1372-04e2. ASTM International, 2002.
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