As part of Building America (BA) research for developing and implementing zero-energy homes on a widespread basis, IBACOS has conducted very detailed modeling to determine the comfort implications of different high-performance exterior wall and window assemblies at this level of construction. IBACOS used TRNSYS software to build a representative two-story house design located in cold, mixed-humid, and hot-dry climate zones. Using the house design, information was obtained on temperature and humidity conditions, which was used to produce comfort indices for each room and determine space-conditioning energy usage. Altogether, 15 wall assemblies were modeled, including double-wall, 2 in. × 8 in. wood-framed, and structural insulated panels (SIPs). The modeled windows feature many of the highest-performance varieties available in the domestic marketplace.

Research results indicate that the comfort benefits for upgrading from standard to higher-performance wall construction are greater in a cold climate zone. In each of the climate zones studied, three wall types equally exhibited the best comfort situations. These walls have a minimum of 2 in. (51 mm) of exterior insulating sheathing, a minimum of 2 in. × 6 in. (38 mm × 140 mm) wood framing, and a nominal thermal performance of at least 41 h·ft²·°F/Btu (7.2 m²·K/W).

Windows with triple glazing, a U-factor of 0.19 Btu/h·°F·ft2 (1.1 W/m²·K) or less, and a solar heat gain coefficient of 0.22 or less provided the best comfort situations in all three climate zones. However, even with these windows, discomfort from overheating occurred in south-facing bedrooms in the hot-dry climate zone, reinforcing the value of exterior and permanent shading devices. Using high solar heat gain windows in the cold climate zone resulted in overheating and discomfort during the shoulder seasons.