Using concrete can facilitate the process of obtaining LEED™ Green Building certification. Leadership in Energy and Environmental Design (LEED) is a point rating system devised by the United States Green Building Council (USGBC) to evaluate the environmental performance of a building and encourage market transformation towards sustainable design. The system is credit-based, allowing projects to earn points for environmentally friendly actions taken during construction and use of a building. LEED was launched in an effort to develop a “consensus-based, market-driven rating system to accelerate the development and implementation of green building practices.” The program is not rigidly structured; not every project must meet identical requirements to qualify.
Three LEED products are currently available:
LEED – NC v2.2 for New Construction and Major Renovations
LEED - CS v1.0 for Core and Shell
LEED – EB v1.0 for Existing Buildings
LEED – CI v1.0 for Commercial Interiors
LEED Canada – NC v1.0 is also available.
The LEED rating system has five main credit categories:
Energy and atmosphere
Materials and resources, and
Indoor environmental quality.
Each category is divided into credits. Detailed information on the LEED program and project certification process is available from USGBC at www.usgbc.org. The program outlines the intent, requirements, technologies, and strategies for meeting each credit. Credits are broken down into individual points. Additional points can be earned for innovation, exceptional environmental performance, and use of a LEED accredited professional on the project team.
Points for Certification for LEED-NC v2.2
A building requires at least 26 points for certification. Silver, gold, and platinum levels are also available.
Credit Category Points Available
Energy and Atmosphere
Materials and Resources
Indoor Environmental Quality
Total Core Points 64
Innovation and Design Process 5
LEED Certification Levels
Certified 26 - 32 Points
Silver 33 - 38 Points
Gold 39 - 51 Points
Platinum 52 - 69 Points
Concrete and LEED
Using concrete can increase the number of points awarded to a building in the LEED system. The following are suggestions for earning LEED-NC v2.2 points through the use of cement and concrete products. The paragraph headings below correspond to the credit categories and the credit numbers in the LEED rating system. Points must be documented according to LEED procedures in order to be earned. The USGBC website, www.usgbc.org, contains a downloadable “letter template” that greatly simplifies the documentation requirements for LEED v2.2. The potential available points that can be earned through the use of concrete range from 19 to 28.
Brownfield Redevelopment (Sustainable Sites Credit 3).
Cement can be used to solidify and stabilize contaminated soils and reduce leaching concentrations to below regulatory levels. Documentation is required indicating the site was contaminated and the remediation performed. This credit is worth 1 point.
Site Development: Protect or Restore Habitat
(Sustainable Sites Credit 5.1).
Concrete parking garages within buildings can be used to limit site disturbance, including earthwork and clearing vegetation. For example, one LEED criterion is to limit site disturbance to 12 m (40 ft) beyond the building perimeter. Parking garages within buildings help maintain existing natural areas that would be consumed by paved parking. This credit is worth 1 point.
Site Development: Maximize Open Space (Sustainable Sites Credit 5.2).
Concrete parking garages on the lower floors of a building can be used to help reduce the footprint of the development. In this context the building footprint includes the building, access roads, and parking. Parking garages within buildings reduce the building footprint by reducing paved parking areas. This requirement can be met by exceeding the local zoning’s open space requirement for the site by 25%. This credit is worth 1 point.
Stormwater Design: Quantity Control (Sustainable Sites Credit 6.1).
The intent of this credit is to limit disruption and pollution of natural water flows by managing stormwater runoff. Using pervious concrete pavements will reduce the rate and quantity of storm water runoff because they increase infiltration of stormwater. Pervious concrete contains coarse aggregate, little or no fine aggregate, and insufficient cement paste to fill the voids between the coarse aggregate. It results in concrete with a high volume of voids (20% to 35%) and a high permeability that allows water to flow through easily. Similar results can be achieved by using concrete grid pavers that have large voids where vegetation can grow. On building sites where the existing imperviousness is greater then 50%, this credit requires reducing the rate and quantity of stormwater runoff by 25%. On building sites where the existing imperviousness is less than 50%, the requirement specifies that the post-development discharge rate and quantity from the site shall not exceed the pre-development rate and quantity. This credit is worth 1 point
|Sustainable Sites Credit 6.1. Water flows freely through a section of pervious pavement.|
Stormwater Design: Quality Control (Sustainable Sites Credit 6.2).
The intent of this credit is similar to that of the one above. Credit is provided if the stormwater management plan captures and treats 90% of the average annual rainfall, and if 80% of the post development total suspended solids (TSS) are removed. Using pervious pavement or grid pavers can contribute to earning this credit, worth 1 point.
Heat Island Effect: Non-Roof (Sustainable Sites Credit 7.1).
This credit requires high reflectance materials (Solar Reflectance Index (SRI) of at least 29) and/or open grid pavement for at least 50% of the site’s non-roof impervious surfaces (hardscape) such as sidewalks, courtyards, parking lots, driveways, and access roads. This requirement can be met by using concrete, high-reflectance pavers, or open-grid pavers rather than asphalt for at least 50% of the impervious surfaces. Another option is to place a minimum of 50% of parking spaces under cover such as underground, under deck, under roof, or under a building. Any roof used to shade or cover parking must have an SRI of at least 29. The SRI is calculated from solar reflectance and emissivity. Solar reflectance is the ratio of the amount of solar radiation reflected from a material to the amount that shines on the material. Solar radiation includes the infrared and ultraviolet as well as the visible spectrum. Generally, light-colored surfaces have a high reflectance, but this is not always the case. Surfaces with lower reflectance absorb more solar radiation. The absorbed radiation is converted into heat and the surface gets hotter. Where paved surfaces are required, using materials with higher reflectance will reduce the heat island effect—consequently saving energy by reducing the demand for air conditioning—and improve air quality. As the temperature of urban areas increases, so does the probability of smog and pollution. Smog episodes rarely occur when the temperature is below 21°C (70°F).
Concrete constructed using ordinary portland cement generally has an SRI of approximately 35, although it can vary. New concrete made with “white” portland cement generally has an SRI of 86. New asphalt generally has an SRI of 0, and weathered asphalt has an SRI of approximately 6. This credit is worth 1 point.
Heat Island Effect: Roof (Sustainable Sites Credit 7.2).
One method of obtaining credit is to install a vegetated roof for at least 50% of the roof area. Concrete roof decks are often needed to provide structural support for the heavy, moist soil in a vegetated roof. Lightweight concrete topping can be used to create a sloping deck to provide drainage for the system. More information on vegetated or green roofs is available at www.greenroofs.org. This credit is worth 1 point.
Minimum Energy Performance (Energy and Atmosphere Prerequisite 2).
All buildings must comply with certain sections on building energy efficiency and performance as required by the ANSI/ASHRAE/IESNA 90.1-2004, Energy Standard for Buildings Except Low-Rise Residential Buildings. In certain cases, local energy codes can be used for compliance if they have been shown to be equivalent or exceed the ASHRAE standard. The requirements of the ASHRAE standard are cost-effective and not particularly stringent for concrete. Insulating to meet or exceed the requirements of the standard is generally a wise business choice. Determining compliance for the envelope components is relatively straightforward using the tables in Chapter 5 of the ASHRAE standard. Minimum requirements are provided for mass and non-mass components such as walls and floors. Components constructed of concrete generally are considered ”mass.“ This means the components have enough heat-storage capacity to moderate daily temperature swings. Buildings constructed of cast-in-place, tilt-up, precast concrete, insulating concrete forms (ICF), or masonry possess thermal mass to help moderate indoor temperature extremes and reduces peak heating and cooling loads. In many climates, these buildings use less energy than non-massive buildings with walls of similar thermal resistance. When buildings are properly designed and optimized, incorporating thermal mass can lead to a reduction in heating, ventilating, and air-conditioning equipment capacity. Reduced equipment capacity can represent energy and construction cost savings. This item is required and is not worth any points.
Optimize Energy Performance (Energy and Atmosphere Credit 1).
This credit is awarded if energy cost savings can be shown compared to a base building that meets the requirements of ASHRAE 90.1-2004. The method of determining energy cost savings must meet the requirements of Appendix G, “Performance Rating Method.” Many engineering consulting firms have the capability to perform whole building energy simulations to determine energy savings as required using a computer based program such as DOE2 or EnergyPlus. When concrete is considered, it is important to use a program like these that calculate yearly energy use on an hourly basis. Such programs are needed to capture the beneficial thermal mass effects of concrete. Insulated concrete systems, used in conjunction with other energy savings measures, will most likely be eligible for points. The number of points awarded will depend on the building, climate, fuel costs, and minimum requirements of the standard. From 1 to 10 points are awarded for energy cost savings of 10.5% to 42% for new buildings and 3.5% to 35% for existing buildings. A small office building under 20,000 sq ft complying with the ASHRAE Advanced Energy Design Guide For Small Office Buildings 2004 (www.ashrae.org
) can achieve 4 points, and a building complying with E-Benchmark v1.1 (www.NewBuildings.org
) can achieve 1 point. Studies show that using concrete walls that are insulated to exceed minimum code requirements by a modest amount (about the same as minimum requirements for frame walls) can contribute to earning 1 to 3 points, depending on the building type, orientation, and climate. Building Reuse (Materials and Resources Credit 1).
The purpose of this credit is to leave the main portion of the building structure and shell in place when renovating. The building shell includes the exterior walls, roof, and framing but excludes window assemblies, interior partition walls, floor coverings, nonstructural roofing material, and ceiling systems. This credit should be obtainable when renovating buildings with concrete walls, since concrete in buildings generally has a long life. This is worth 1 point if 75% of the existing building structure/shell is left in place and 2 points if 95% is left in place.
Construction Waste Management (Materials and Resources Credit 2).
This credit is received for diverting construction and demolition debris from landfill disposal. It is awarded based on diverting at least 50% by weight or volume of the above listed materials. Since concrete is a massive construction material and is frequently crushed and recycled into aggregate for road bases or construction fill, this credit should be obtainable when concrete buildings are demolished. This credit is worth 1 point if 50% of the construction and demolition debris is recycled or salvaged and 2 points for 75%.
|Materials and Resources Credit 2. The picture shows machinery taking portions of concrete walls, columns, and floors and crushing them to be used as fill material.|
(Materials and Resources Credit 4).
The requirements of this credit are for using materials with recycled content. One point is awarded if the sum of the post-consumer recycled content plus one-half of the pre-consumer recycled content constitutes at least 10% (based on cost) of the total value of the materials in the project. The value of the recycled content of a material is the weight of the recycled content in the item divided by the weight of all materials in that item, and then multiplied by the total cost of the item. Supplementary cementitious materials, such as fly ash, silica fume, and slag cement are considered pre-consumer. LEED-NC v2.2 allows the recycled content of concrete to be based on the recycled content of the cementitious materials. An example calculation is provided in the LEED-NC v2.2 Reference Guide. Furthermore, using recycled concrete or slag as aggregate instead of extracted aggregates would qualify as post-consumer. Although most reinforcing bars are manufactured from recycled steel, in LEED, reinforcing is not considered part of concrete. Reinforcing material should be considered as a separate item. This credit is worth 1 point for the quantities quoted above and 2 points if the quantities are doubled to 20%.
Regional Materials (Materials and Resources Credit 5).
This credit supports the use of indigenous (local) materials and reduced transportation distances. The requirements of this credit state: ” Use building materials or products that have been extracted, harvested or recovered, as well as manufactured, within 500 miles (800 km) of the project site for a minimum of 10% (based on cost) of the total materials value.” Concrete will qualify if ready-mix and precast plants are within 800 km (500 miles) of a job site, and if the materials to make the concrete were extracted within 800 km (500 miles). Aggregates (sand and gravel) are usually extracted within this distance, and cement and supplementary cementitious materials are usually manufactured within this distance. Calculations can also include concrete either manufactured or extracted locally. This credit is worth 1 point for the quantities quoted above, and 2 points for double the amount, or 20%.
Low-Emitting Materials: Paints & Coatings
(Indoor Environmental Quality Credit 4.2)
This credit reduces indoor air contaminants that are odorous, irritating and/or harmful to the comfort and well-being of installers and occupants. Although it specifies low VOC coatings for use on the interior of a building, concrete walls and ceilings with no coatings also contribute to this credit. The credit is worth 1 point if paints and coatings meet the specified criteria.
Low-Emitting Materials (Indoor Environmental Quality Credit 4.3)
This credit also reduces indoor air contaminants that are odorous, irritating and/or harmful to the comfort and well-being of installers and occupants. Although the intent is for low VOC carpet, USGBC has indicated that flooring surfaces other than carpet that can demonstrate equivalent performance to the Carpet & Rug Institute Green Label Program may be substituted as an alternative compliance path to achieve this credit. This credit is worth 1 point.
Concrete can also be used to obtain points indirectly. For example, concrete can be used as cisterns to collect rainwater or greywater for Water Efficiency Credit 1: Water Efficient Landscaping. Concrete can be used as tanks for rainwater, greywater, or sewage for Water Efficiency Credit 2: Innovative Wastewater Technologies. Bio-based form-release agents are available that can contribute to Materials and Resources Credit 6: Rapidly Renewable Materials. The thermal mass of concrete contributes to Indoor Environmental Quality Credit 7: Thermal Comfort.
In addition to the points discussed above, 4 points are available as Innovation in Design (ID) Credits. These points can be applied for if an innovative green design strategy is used that does not fit into the point structure of the five LEED categories or if it goes significantly beyond a credit requirement and demonstrates exceptional environmental performance. For example, the USGBC has indicated that the durability credit (MR 8) allowed in LEED Canada-NC v1.0 can be used as an ID credit in LEED-NC v2.2. USGBC has also indicated that an ID credit may be allowed for concrete walls and ceilings with no paints or coatings on the interior. In addition, one point is also provided if a principal participant of the project team is a LEED Accredited Professional. The concrete industry has LEED-experienced professionals available to help maximize the points for concrete.
Benefits of LEED Certification
LEED is a voluntary program; however, obtaining a LEED certification projects a positive environmental image to the community. Additionally, meeting many of the green building practices can result in energy and cost savings over the life of the structure. Other advantages include better indoor air quality and plenty of daylight.
Studies have shown that workers in these environments have increased labor productivity, job retention, and days worked. These benefits contribute directly to a company’s profits because salaries—which are about ten times higher than rent, utilities, and maintenance combined—are the largest expense for most companies occupying office space. In addition, students in these environments have higher test scores and lower absenteeism. Retail sales are higher in daylit buildings.
Many cities and states either provide tax credits or grants for green buildings, or require green building certification for public buildings. The U.S. government is adopting green building programs similar to LEED through the General Services Administration (which owns or leases over 8300 buildings), the U.S. Army, the Department of State, the Department of Energy (DOE), and the Environmental Protection Agency (EPA). Eight states including California, New York, Oregon, and Washington have adopted its use for public buildings. Many agencies are requiring LEED silver certification as a minimum. Thirteen countries have expressed interest in LEED including China and India; these countries have exceptionally high new building construction. Conditions vary and the list is growing, so please contact local jurisdictions or USGBC for details. Support for green buildings has increased rapidly each year over the last five years.
The LEED Green Building Rating System for New Construction, Version 2.2, promotes environmentally sustainable buildings for the improvement of outdoor and indoor building quality, the conservation of resources, and the reduction of waste during the building process. Concrete can be used in conjunction with the LEED program to earn a LEED certification.
LEED– New Construction (NC) v2.2 - Project Checklist
How Concrete Can Contribute to Points
†Up to 2 additional points can be earned, must be submitted and approved (not included in total)
||Site Development, Protect or Restore Habitat
||Site Development, Maximize Open Space
||Stormwater Design, Quantity Control
||Stormwater Design, Quality Control
||Heat Island Effect, Non-roof
|Energy and Atmosphere|
||Minimum Energy Performance
||Optimize Energy Performance
||1 - 10|
|Materials and Resources|
||Building Reuse, Maintain 75% of Existing Walls, Floors, and Roof
||Building Reuse, Maintain 95% of Existing Walls, Floors, and Roof
||Construction Waste Management, Divert 50%
||Construction Waste Management, Divert 75%
||Recycled Content, 10% (post-consumer plus ½ pre-consumer)
||Recycled Content, 20% (post-consumer plus ½ pre-consumer)
||Regional Materials, 10%
||Regional Materials, 20%
|Innovation and Design Process|
||Concrete walls and ceiling with no coating
|Credit 1.3 - 1.4
||Apply for other credits demonstrating exceptional performance
||LEED Accredited Professional
||19 - 28|