Green Homebuilding: A Comparison of LEED for Homes and NAHB's National Green Building Standard
The National Association of Home Builders (NAHB), in conjunction with the International Code Council (ICC), recently introduced changes to its green building standard. The new standard, known as the National Green Building Standard or ICC-700, was approved by the American National Standards Institute (ANSI) in late January 2009 and replaces NAHB's 2005 green building standard. Eleven months prior to this unveiling, the U.S. Green Building Council (USGBC) officially adopted its LEED (Leadership in Energy & Environmental Design) for Homes standard. The LEED for Homes program had been in its pilot phase for two years before its formal adoption. While there are some slight differences between these two third-party rating systems, both organizations seek to guide green homebuilding with similar processes and design objectives.
The LEED for Homes standard measures green homebuilding performance based on eight categories: site selection, water efficiency, materials and resources, energy and atmosphere, indoor environmental quality, location and linkages, awareness and education, and innovation. Within each of these areas, projects earn points toward certification in four ascending point accumulation levels: Certified, Silver, Gold, and Platinum, with Platinum representing the highest level of achievement. While the USGBC launched LEED v3 in April 2009, a comprehensive upgrade to its commercial and institutional LEED rating systems, the LEED for Homes rating system was not included in that overhaul. According to the USGBC, the next version of LEED for Homes is currently in development and is slated for release in 2011.
Like LEED for Homes, ICC-700 establishes a national rating system for residential green building. The NAHB and ICC standard applies to a variety of residential projects, including site development, multifamily housing projects, remodeling, single-family homes, and subdivisions. ICC-700 has four compliance levels: Bronze, Silver, Gold, and Emerald, with Emerald representing the highest level of achievement. The standard includes a list of mandatory measures, most of which correspond to various minimum code requirements. Developers accrue points by incorporating features in six areas: lot design and development, water efficiency, energy conservation, resource conservation, indoor environmental quality, and homeowner education. A seventh category, site design and development, applies to residential subdivisions, mixed-use developments, and master planned communities. Similar to the LEED structure, the more points a project accumulates under the ICC-700 standard, the higher the certification it earns. An added consideration under ICC-700 is that houses over 4,000 square feet will need more points for a given certification level than smaller houses.
Both LEED for Homes and ICC-700 set forth a variety of goals for residential projects, such as promoting energy efficiency, providing healthy indoor air quality, reusing and recycling materials and resources, incorporating water efficiency techniques, and adopting site selection and development strategies that minimize the impact to the site and the surrounding area. While the majority of these goals are measured evenly nationwide, several depend on regional factors, such as climate zones, precipitation figures, radon potential, and termite infestation probability. As an example, many of the energy efficiency components of the standards depend largely on climate zone. Achieving a particular level of energy efficiency may yield more points in one climate zone than in another. Maryland and Washington, D.C. are located in Climate Zone 4. Incorporating energy efficient HVAC equipment into a project in Maryland or D.C. (Climate Zone 4) will yield more points for that project than the same equipment would yield for a project in South Carolina (Climate Zone 3), simply because of the differentiation in climate zones.
A cursory review of both standards reveals that many of the goals and strategies are similar, if not identical. Upon closer examination, however, some slight differences surface. Under ICC-700, energy efficiency is demonstrated by percentage reduction in use, using a home that minimally complies with the 2006 International Energy Conservation Code (IECC) as the baseline. The LEED for Homes standard uses a similar methodology for demonstrating energy efficiency, except that it uses the 2004 IECC as the baseline. Another noteworthy distinction is the online scoring tool provided by the NAHB Research Center under ICC-700. The tool is free and is aimed at simplifying implementation. The tool provides a preliminary score for a project to give the developer an approximation of the level for which the project will qualify. Developers can then make adjustments to the project, as necessary. LEED for Homes does not have a comparable measuring feature that applicants can use in planning
their projects.
As both of the green home standards are relatively new, energy consultants have not yet determined how they compare in terms of overall cost and efficiency. Some estimate, however, that the basic ICC-700 standard house will be very close to a LEED for Homes Certified house. Representatives from both the USGBC and NAHB assert that, while the standards differ in their approach, they share a common goal of providing a mechanism for recognizing high-performance green homes. What is clear at this point is that developers now have some flexibility to choose a green home standard that appropriately fits their projects.