The U.S. Green Building Council (USGBC) developed Leadership in Energy and Environmental Design (LEED) Green Building Rating systems to assist with market transformation to a more stable, efficient, and environmentally sound approach to design and construction. The LEED products are voluntary, consensus-based systems used as standards for certification and design guides for sustainable construction and operation.
LEED includes a growing portfolio of rating products serving specific market sectors:
- New Construction (LEED-NC)
- Existing Buildings (LEED-EB)
- Commercial Interiors (LEED-CI)
- Core & Shell (LEED-CS)
- Homes (LEED-H)
- Neighborhood Development (LEED-NH)
Note: With its rigorous metrics, LEED rating systems are emerging as a key means to measure sustainable design practice. Other paths include Green Globes and Energy Star.
The LEED-NC rating system assigns points to aspects of sustainable performance in six categories:
- Sustainable Sites
- Water Efficiency
- Energy and Atmosphere
- Materials and Resources
- Indoor Environmental Quality
- Innovation and Design
To achieve LEED certification, project teams must satisfactorily document achievement of all the LEED prerequisites and a minimum number of points. Project teams submit design concepts and plans to the USGBC, often assisted by a LEED Accredited Professional (LEED AP). USGBC assigns an expected rating to the project, and gives a formal rating after the team completes a construction submittal.
LEED-NC certifies buildings to four levels of increasing sustainable performance:
- Certified (26–32 points)
- Silver (33–38 points)
- Gold (39–51 points)
- Platinum (52–69 points)
- minimally disrupts the site (area and time)
- reduces damage to drainage paths and natural habitats
- increases open area when multi-level parking structures are used
- reduces the heat-island effect because of concrete's light color
- improves energy efficiency and thermal comfort
- reuses and recycles formwork, keeping materials out of the landfill
- uses recyclable concrete and steel
- can be reused or recycled
- can use waste and recycled materials such as slag, fly ash, and silica fume
- is generally made from materials that are extracted and manufactured regionally
- does not off-gas, and does not need to be sealed or painted
Precast concrete and other materials contribute to LEED points by providing performance and properties that are measured by the LEED program. At this time, PCI endorses potential precast concrete contributions for up to 20 LEED points (see LEED Project Checklist) and possibly more, depending on the project.
For a detailed discussion of precast concrete’s contributions to green building practices, including LEED points, please refer to "Achieving Sustainability with Precast Concrete" by Martha VanGeem, CTL Group, which was published in the January–February 2006 issue of the PCI Journal.
6. How can precast concrete reduce the heat-island effect described in the LEED Sustainable Sites credit (SSc7.1)?
Sustainable Sites credit 7.1 is intended to reduce heat islands, meaning the thermal gradient difference between developed and undeveloped areas. The heat-island effect is partially attributed to the dark surfaces of roofing and paving, and the additional heat in developed areas increases HVAC loads and contributes to the creation of smog. Reducing heat islands minimizes impact on microclimate and human and wildlife habitat.
Precast concrete parking structures that place at least 50% of the spaces under cover (for example, underground, under a building, or under a deck or roof) can reduce this effect. Any roof used to shade or cover parking must have a solar reflective index (SRI or albedo) of at least 29. In addition, high-albedo vertical precast concrete wall surfaces reduce the heat-island effect.
Yes, under the recycled content credit MR 4.1 and 4.2
8. Is the 500-mile-radius requirement for local-material content limited to the finished precast concrete product, or does it also apply to the raw materials?
Credit MR 5.1-5.2 applies to all materials extracted, processed, and manufactured within a 500-mile radius of the project site.
Projects earn Innovation and Design credits when they demonstrate exemplary performance in a recognized LEED credit area, or bring new approaches and technologies such as carbon-fiber reinforcing that reduce weight and embedded energy and advance sustainable design. Because of its significant contributions to LEED, and its inherent green characteristics, precast concrete offers an excellent platform on which creative project teams can base their sustainable design plans.
10. How does precast concrete contribute to the underlying sustainability concept of "Reduce, Reuse, Recycle"?
By reducing the amount of materials and the toxicity of waste materials. Precast concrete can be designed to optimize (lessen) the amount of concrete used in a structure or element. As one example, the use of carbon-fiber reinforcement or insulation can reduce:
- Amount of concrete needed in a precast concrete panel
- Weight of a precast concrete panel
- Transportation cost of precast concrete panel
- Amount of energy used to erect a precast concrete panel
Precast concrete generates low amounts of waste with low toxicity
- 2% of the concrete at a precast plant is waste
- 95% of the waste is used to manufacture new panels
- By reusing products and containers and repairing what can be reused
- Precast concrete panels can be reused when buildings are expanded or dismantled
- Concrete pieces from demolished structures can be reused to protect shorelines
- Wood or fiberglass formwork used to make precast concrete products is generally reused 40 or more times
- Concrete and steel have practically unlimited service lives
- By recycling as much as possible, including buying products with recycled content
- Industrial wastes (fly ash, slag, and silica fume) can be used as partial replacements for cement
- Wood and steel forms are recycled when they become worn or obsolete
- Virtually all reinforcing steel is made from recycled steel
- Insulation contains partially recycled material
- Concrete in most urban areas is recycled as fill or road base