A new report from the nonprofit Urban Green Council, the New York chapter of the USGBC, is the latest from the local group of developers, architects, and contractors pushing for better-performing envelopes in New York City and elsewhere. Titled “High Cholesterol Buildings” and targeting glass-clad structures, the report claims that because a building’s envelope is likely to outlast its mechanical systems, the continued use of traditionally inefficient cladding, such as glass, could stymie the progressive, positive environmental impact of the rest of the structure.
The report calls out an option in the city’s construction codes, which follow the International Building Code, for design teams to choose either a prescriptive-based or a flexible performance-based compliance track. According to the report, teams that choose the latter path could trade an envelope with less transparent-glass area for one with sweeping views to the outside, supplementing the resulting solar-heat gain with better-performing mechanical systems.
Urban Green uses the report to plug a recommendation—iterated in February 2010 with the NYC Green Codes Task Force report and again in October 2013 with the group’s Building Resiliency Task Force report—proposing a whole-building U-value applied to projects using energy modeling through the performance path. The Wall Street Journal reports that the city’s construction code requires the use of the performance path for projects whose envelopes are more than 40-percent glass but that the envelopes of some of the latest glass towers to rise in the city contain up to 70-percent glazing.
“The sensible theory behind our dual-track energy code—that what matters is achieving the energy performance goal, not how one gets there—would say that the envelope-mechanical system tradeoff doesn’t matter,” the report states. “But there are unintended consequences.”
As other building systems are upgraded the envelope risks becoming stagnant and, as a result, accounting for a greater share of the structure’s energy consumption. The report suggests strategic use of spandrel glass; education for trades on air-sealing and eliminating thermal breaks; improved reflectivity and visible light transmittance of glass; the incorporation of low, interior window sills to break up glass expanses without sacrificing views; and the passage of “greener” codes as ways to bring the envelope up to speed.