Precast LEEDs the way.
By Dean A. Frank, P.E.
What exactly is sustainable development – other than a construction industry buzz word? Merriam-Webster defines “sustainable” as: of, relating to, or being a method of harvesting or using a resource so that the resource is not depleted or permanently damaged. As such, sustainable development means building for today and in the future in a manner that does not deplete the resources needed for construction.
Why is sustainable development getting so much attention? Currently in the United States, new and existing buildings require significant amounts of energy and materials. U.S. buildings account for the following:
• 36 percent of total energy use, which includes 65 percent of electricity consumption
• 30 percent of greenhouse gas emissions
• 30 percent of raw materials
• 30 percent of waste output per 136 million tons annually
• 12 percent of potable water consumption
• 136 million tons of construction and demolition waste (approximately 2.8 pounds per person, per day)
Because of these facts, more emphasis is being placed on green building practices, which includes efficient use of energy, water and materials; limited impact on the outdoor environment; and a healthier indoor environment. The use of precast concrete contributes to reducing dependence on these resources, and precast is a sensible choice for sustainable development. Concrete is a very durable material, which is a significant sustainable attribute. It will not rust, rot or burn, and it will outlast most other building materials, including wood and steel. This results in less energy and resources over time to repair or replace a building or its components.
Also, insulated concrete buildings generally require less energy to heat and cool because they do not experience large daily interior temperature fluctuations. In addition, concrete often contains manufacturing byproducts such as fly ash and blast furnace slag that would otherwise find their way to a landfill. Precast concrete manufacturing typically produces few byproducts, and both the concrete itself and the steel reinforcement inside it are recyclable.
It’s important to point out that there is one misconception associated with the cement used in concrete. Although there is no question that the cement manufacturing process requires a significant amount of energy and results in carbon dioxide emissions, when compared to wood and steel, concrete is quite favorable.
According to the Department of Energy, U.S. cement production accounts for 0.33 percent of energy consumption. This is lower than for both wood production at 0.5 percent and steel production at 1.8 percent. The cement industry has reduced carbon dioxide emissions and energy usage by 33 percent since 1975 and is continually striving to make further reductions. In addition, acquiring the raw materials for concrete places less stress on the environment compared with steel or wood production.
In the past, green building techniques were rather loosely defined. So, in an effort to provide a standard of measurement, the Leadership in Energy and Environmental Design (LEED) Green Building Rating System was developed in 1998. It is a voluntary, consensus-based national standard for developing high-performance, sustainable buildings. This system is popular in both public and private construction specifications.
LEED credits fall into the following categories: Sustainable Sites; Water Efficiency, Energy & Atmosphere; Materials & Resources; Indoor Environmental Quality; and Innovation & Design Process. Within each of these six categories, between 5 and 17 credits can be earned with certain levels of compliance with the various subcategories. LEED certification can be garnered at four levels, as follows:
Certified: 26-32 points
Silver: 33-38 points
Gold: 39-51 points
Platinum: 52-69 points
Precast concrete products correlate directly with at least four LEED credits and a total of eight points in the following areas: Site Credit 6, Stormwater Management; Site Credit 7, Heat Island Reduction; Materials & Resources Credit 4, Recycled Content; and Materials and Resources Credit 5, Regional Materials. In addition, the use of precast concrete may contribute to LEED Innovation Points.
It has been known for a long time that building with concrete offers many benefits, including:
• Resistance to mold and moisture decay
• Energy savings associated with concrete’s thermal mass
• Fire resistance
• Noise reduction
• Low maintenance
Precast concrete is often preferred over cast-in-place construction because of precast’s many environmental attributes. Precast plants reuse formwork, in itself a conservationist move, and in doing so reduce construction waste that would otherwise be generated at a job site. Because precast concrete components are modular and standardized, they are installed in a quicker fashion and result in reduced construction times and energy usage and emissions from on-site equipment. These benefits have a secondary advantage in that they may help gain additional LEED points in the Material & Resources Credit 2, Construction Waste Management, and Credit 7, Certified Wood.
Precast concrete products are increasingly specified in building construction, used because of their inherent quality, value and permanence. For more information on precast concrete construction, please contact NPCA at (800) 366-7731.