Article No: 239
Sustainable Concrete Solutions Contribute to LEED for Homes Certification: Part II
By: Donn C. Thompson AIA, LEED AP
In Part I we identified the overall objectives the U.S. Green Building Council hopes to achieve through the release of LEED for Homes (LEED-H), its first single-family residential green building program. The potential compliance benefits that may be available from concrete technologies was identified for the following LEED-H Resource Categories: Innovation and Design Process, Location and Linkages, and Sustainable Sites.
In Part II we focus on the additional solutions concrete home-building systems can have in helping project earn points under the remaining applicable LEED-H categories. Less complicated compliance with a variety of conformance criteria identified under Water Efficiency, Energy and Atmosphere, Material and Resources, and Indoor Environmental Quality are outlined in detail below and summarized in Table 2b.
WE – WATER EFFICIENCY
WE 1.1 Rainwater Harvesting System and/or WE 1.2 Graywater Reuse System: Waste water that is not clean, but not heavily polluted, like water from laundry or bathing is called graywater. The capture and control of graywater and rainwater can greatly reduce water usage requirements for a home and site. Concrete cisterns are an excellent choice for non-potable harvesting of such runoff. A home can qualify for 4 points when an exterior collection system is large enough to hold runoff of at least 75 percent of the roof area of the house from a 1-inch rainwater event. The home qualifies for an additional point if graywater is harvested on site and reused within the house.
EA – ENERGY AND ATMOSPHERE
EA-1.1 Optimize Energy Performance: At a minimum, LEED-H requires houses to meet the requirements of an Energy Star home, 15 percent more energy efficient than a home built to the requirements of the 2004 International Energy Conservation Code (IECC). To earn Energy and Atmosphere credits, a home must exceed these minimum requirements. Between 2 and 34 LEED-H points can be awarded based on the demonstrated energy efficiency of the house by building to exceed Energy Star performance requirements or by following prescriptive requirements of the various EA subcategories pertaining to energy performance.
Concrete home-building systems are energy efficient because of their unique ability to combine high R-values, very low air infiltration, and thermal mass benefits in the exterior walls. To fully capture these benefits designers and builders should follow the LEED-H performance requirements with a modeling program that will adequately measure and credit thermal mass benefits. Unlike wood or steel frame systems, concrete construction is largely continuous, with far fewer joints and seams, resulting in tighter construction. Finally, the concrete itself absorbs and stores heat energy, delaying the impact of exterior temperatures on the interior environment, which reduces heating and cooling loads.
EA 2.0 Insulation and EA 3.0 Air Infiltration: With wood and steel framing, careful attention must be paid to the elaborate installation of insulation, air barriers, and their placement behind tubs, showers, fireplaces, and staircases. With the inherent continuity of insulation and air barrier in concrete wall systems, these time-consuming difficulties are eliminated. The on-site detailing is simpler, requiring less skilled labor than with stick built construction. Required LEED-H inspection procedures become less demanding with concrete wall systems as well.
MR – MATERIAL AND RESOURCES
MR 1.5.B Off-Site Fabrication: To reduce construction waste, LEED-H provides credits for panelized construction as an alternative to on-site framing. Four points are awarded for the use of modular, prefabricated construction systems for all principal building sections. Panelized concrete wall, floor, and roof systems can all be manufactured off site, then shipped to the job and craned into place quickly, with minimal site disturbance, and no waste. Other site-built concrete systems can be effectively managed during installation to greatly reduce the amount of debris generated in contrast to conventional frame construction. Points for these site-built systems can be obtained by submitting a credit interpretation to USGBC demonstrating the comparative amounts of framing materials saved, the reduced number and size of thermal breaks, and the increased amounts of insulation.
MR 2.2 Environmentally Preferable Materials: The combination of recycled content, low emissions, and locally derived materials available with many concrete products can contribute to multiple points for a typical LEED-H project. The rating system outlines where suitable environmentally preferable products can be used within a LEED home. In order to contribute, concrete used in exterior walls and foundations must contain at least 30 percent industrial byproducts such as fly ash or slag cement. Fiber cement siding, concrete masonry, patios, countertops, and roof tiles containing recycled materials all garner points as well as the use of sealed concrete floors. All of the above concrete technologies can also apply toward additional credit if they meet the LEED for Homes requirements for locally derived materials.
MR 3.2 Construction Waste Reduction: Debris from a variety of concrete products used in construction can be diverted from landfills and recycled. Concrete products and ready-mix concrete are delivered to the site in the quantity needed, resulting in less site waste than frame construction. Any excess concrete is frequently collected, crushed and used as base material or fill. The foam from insulating concrete form systems can be collected and reground and reused in new foam applications. By reducing the amount of wasted materials, these systems will contribute to up to 3 points available for this category.
EQ – INDOOR ENVIRONMENTAL QUALITY
EQ 1.0 Energy Star with Indoor Air Package: A concrete home-building project can receive 13 LEED-H credits by complying with the various requirements of the Environmental Protection Agency’s (EPA), Indoor Air Package. These requirements include a durable exterior envelope, one with strength, longevity, and effective interior and exterior moisture control capability and resistance. Previously discussed benefits like control of air infiltration, non-toxic pest control measures, and low VOC finishes like sealed concrete floors are all critical components to improved indoor air quality as well.
By using concrete systems and finishes, homebuilders and designers can more easily achieve LEED-H certification for their homes. Whether through contribution based on the resource categories outlined in these two articles, or through accepted submissions for sustainable innovation credits, a concrete home provides the long term, high quality residential performance the USGBC is striving to encourage with LEED for Homes.
The information presented in this article is intended to highlight and summarize the ways in which concrete can contribute to the ability of a home to qualify for points under LEED for Homes. The reader should consult the latest version of LEED-H directly for specific compliance requirements. More detail can be found at the U.S. Green Building Council web site, usgbc.org. For more information on cement and sustainability visit the Concrete Thinker site at concretethinker.com.