LEED^® Point Rating System

Building "Green" with Concrete

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 or site.  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 by the USGBC to develop a "consensus-based, market-driven rating system to accelerate the development and implementation of green building practices."

The LEED rating system has five main credit categories: sustainable sites, water efficiency, 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 processes is available on the USGBC website, www.usgbc.org.  The program outlines intent, requirements, technologies and strategies for meeting each credit.  Additional points can be earned for innovation and use of a LEED-accredited professional on the project team.

Using concrete can increase the number of points awarded to a building in the LEED system.  The potential available points that can be earned through the use of concrete range from 11 to 21.  A breakdown of the five major categories and how concrete can be used to obtain points in each of them is included below.  The following cities and states either provide tax credits and grants for green buildings or require public buildings to be LEED-certified: Massachusetts, New York, Chicago, Pennsylvania, Los Angeles, Portland, San Diego, San Jose and Seattle.  Conditions vary and the list is continually growing, so please contact your local jurisdiction for details!

Sustainable Sites Credit 6.1: Stormwater Management Rate & Quality

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 stormwater runoff because they increase infiltration of stormwater.  Pervious concrete contains coarse aggregate, little or no fine aggregate and just enough paste to coat the aggregate and bind them together.  It results in a concrete with  high volume of voids (15% to upwards of 30%) and a high permeability that allows water to flow through easily.  This credit is worth one point.

Materials Credit 2: Construction Waste Management

This credit is extended for diverting construction, demolition and land clearing waste from landfill disposal.  It is awarded based upon diverting at least 50% by weight of the above listed materials.  Since concrete is a relatively heavy construction material and is frequently crushed and recycled into aggregate for road bases or construction fill, this credit should be obtainable when concrete buildings/pavements are demolished.  This credit is worth one point if 50% of the waste is recycled or salvaged and two points for 75%.

For concrete, either the credit for building reuse or the credit for construction waste management can be applied for, but not both; this is because the concrete structure is either reused or recycled into another use.

Materials Credit 4: Recycled Content

The requirements for this credit state "use materials with recycled content such that post-consumer recycled content constitutes at least 5% of the total value of the materials in the project OR combined post-consumer and one-half of the post-industrial recycled content constitutes at least 10%."

This percentage is determined by multiplying the cost of an item by the percent of recycled materials (on a mass basis) that make up that item.  Supplementary cementitious materials such as fly ash, silica fume and slag cement are considered post-industrial.  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 one point for the quantities quoted above and two points for an additional 5% post-consumer recycled content OR an additional 10% combined post-consumer and one-half post-industrial recycled content.

Materials Credit 5: Local/Regional Materials

The requirements of this credit states "use a minimum of 20% of building materials that are manufactured regionally within a radius of 800 km (500 miles)."

This means that a ready mixed or precast concrete plant within 800 km (500 miles) of the building would qualify.  Concrete will usually qualify since ready mixed concrete plants are generally within 80 km (50 miles) of a jobsite.  The percentage of materials is calculated on a cost basis.  This credit is worth one point.

An additional point is earned if 50% of the regionally manufactured materials are extracted, harvested or recovered within 800 km (500 miles).  Ready mixed concrete plants in the Carolinas generally use aggregates, cements, supplementary cementitious materials and chemical admixtures all which are extracted and/or produced within 800 km (500 miles) of the plant.

Sustainable Sites Credit 7.1: Landscape & Exterior Design to Reduce Heat Islands

"...Use light-colored/high albedo materials (reflectance of at least 0.3) for 30% of the site's non-roof impervious surfaces."

This requirement can be met by using concrete rather than asphalt for 30% or greater of all sidewalks, parking lots, drives and other impervious surfaces.

Albedo, which in this context is synonymous with solar reflectance, is the ratio of the amount of solar radiation reflected from a material to the amount tat shines on the material.  Solar radiation includes the ultraviolet, as well as the visible, spectrum.  Generally, light-colored surfaces have a high albedo, but this is not always the case.  Surfaces with lower albedos 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 albedos will reduce the heat island effect - consequently saving energy by reducing the demand for air conditioning - and improve air quality.

Concrete generally has a reflectance of approximately 0.35, although it can vary.  Measured values are reported in the range of 0.4 to 0.5.  For "white" portland cement, values are reported in the range of 0.7 to 0.8.  New asphalt generally has a reflectance of approximately 0.05, and asphalt five or more years old has a reflectance of approximately 0.10 to 0.15.  This credit is worth one point.