A home in climate zone 2’s window-to-floor area ratio increases from 10% to 30%. What is necessary to qualify for the Energy and Atmosphere Credit…

The LEED for Homes rating system provides prescriptive pathways for credits, including the Energy and Atmosphere (EA) credit for high-performance windows. The requirements are based on the project's climate zone and its window-to-floor area ratio (WFR). As the WFR increases, the building is more susceptible to heat loss and gain through the glazing. To compensate for this larger glazed area and maintain a high level of energy performance, LEED mandates windows with superior insulating properties. For Climate Zone 2, the LEED v4 and v4.1 reference guides show that as the WFR increases beyond the 15% threshold, the maximum allowable U-factor decreases, indicating a more stringent requirement for insulation.

A. A less stringent U-factor would allow more heat transfer, which is counterproductive to energy efficiency, especially with a larger window area.

C. A less stringent solar heat gain coefficient (SHGC) would increase cooling loads in a hot climate (Zone 2), which is contrary to the credit's intent.

D. While a low SHGC is required in Climate Zone 2, the LEED prescriptive tables for this specific zone do not make the SHGC requirement more stringent as WFR increases; it remains constant.

1. U.S. Green Building Council. (2016). LEED v4 for Homes Design and Construction. Washington, DC: USGBC. Page 93, EA Credit: Windows, Table 1 "Prescriptive Window Performance." The table specifies for Climate Zone 2 that as the WFR increases from the "≤15%" category to the ">22%" category, the required U-factor becomes more stringent (decreasing from ≤0.40 to ≤0.32), while the SHGC requirement remains constant at ≤0.25.

2. U.S. Green Building Council. (2021). LEED v4.1 Residential Single Family. Washington, DC: USGBC. Page 101, EA Credit: High-Performance Windows, Table 1 "Prescriptive window performance." This updated guide shows for Climate Zone 2, as WFR increases from "≤15%" to ">15%", the U-factor requirement becomes more stringent (≤0.30 to ≤0.27), while the SHGC requirement stays at ≤0.25.