NAHB and LEED for Homes Equivalent Except on Energy, Says Report
The Cincinnati chapter of The American Institute of Architects (AIA) has published the first comprehensive comparison of the two largest, nationwide green building rating systems for homes. The report looks at the U.S. Green Building Council’s LEED for Homes rating system and the National Green Building Standard (NGBS), developed by the National Association of Home Builders (NAHB), and finds them to be largely similar but with key differences on energy performance.
As the report attests, LEED for Homes requires site-tested minimum energy performance, while NGBS does not. At the same time, the report notes that NGBS is less expensive (by about $800) than LEED for Homes and certification generally takes less time. However, the report notes that to make the systems roughly equivalent on energy, you would have to add Energy Star certification to NGBS—and that eats into the cost difference. Ann Edminster, a residential architect and the principal author of LEED for Homes, told EBN, “In effect, the cost difference is tied to the performance differences, which makes perfect sense. Set a higher bar and it will cost more, both to achieve it and to verify it.”
The report also found that some points available in NGBS were awarded for practices that are required by building code in Ohio—and likely also in other states. According to the authors, this “tends to minimize the strength of the environmental intent of the NGBS Rating System and leans toward an easy rating system versus a rigorous rating system.” However, NGBS requires that buildings pursue extra points in all categories to achieve a higher level of certification, while LEED for Homes simply requires more points overall for higher levels.
Both systems penalize large homes but in slightly different ways. LEED for Homes adjusts the points necessary for each tier of certification based on house size and number of bedrooms. Under this system, an “average” home (one that is neither penalized nor rewarded) ranges from a 900 ft2 (83 m2), one-bedroom house to a 2,850 ft2 (265 m2), five-bedroom house. A 4,030 ft2 (370 m2) house with five bedrooms would need to earn nine more points than an “average” house to earn the same level of certification—a significant handicap in the 100-point system. By contrast, NGBS awards points to all houses smaller than 2,500 ft2 (230 m2), regardless of the number of bedrooms, and penalizes homes over 4,000 ft2 (370 m2).
Carl Seville, a builder and consultant familiar with both systems, told EBN that beyond those differences, the systems also share some weaknesses. “Both programs provide opportunities to game the system by essentially buying points to reach a level of certification.” LEED for Homes, he continued, has fewer available points that NGBS, so “there are some serious imbalances” where actions that require drastically different amounts of time, money, and effort are worth the same amount in points. Seville noted that a project can obtain a point in LEED for Homes either by putting a timer on a bath fan, for example, or by having the entire duct system tested and balanced—a task likely to be both more expensive and more beneficial.
As for the experience of certifying a building in each system, Seville told EBN, “NAHB has much less required documentation, and the requirements are more vague than LEED,” leading, he says, to “a potentially less rigorous certification process.” By comparison, Seville finds LEED “overly administratively heavy” but has fewer concerns about rigor.
The City of Cincinnati commissioned the report to assess whether NGBS could make homes eligible for tax benefits already given to homes certified through LEED. AIA Cincinnati recommends in its report that NGBS can be used to qualify homes for the tax benefits but with added provisions to ensure energy performance: an added Energy Star certification for new homes and a minimum HERS Index for renovations (since Energy Star doesn’t have a certification for renovations).
For more information:
Comparison of LEED for Homes and National Green Building Standard