Environmental Impacts over the Life Cycle of Residential Buildings Using Different Exterior Wall Systems

This study analyzed the environmental impacts of a single-story residential building using different exterior wall systems. The environmental impacts over the complete life cycle of the residential buildings were determined and compared using the following indicators: air pollution index, energy consumption (embodied and operational), global warming potential, resource use, solid waste emissions, and water pollution index. The exterior wall systems analyzed were concrete block, poured in-place concrete, insulated concrete, traditional $0.05\text{m}\times 0.1\text{m}$ by 0.4 m ( $2\text{in}\text{.}\times 4\text{in}\text{.}$ by 16 in.) on center wood frame, traditional $0.05\text{m}\times 0.15\text{m}$ by 0.6 m ( $2\text{in}\text{.}\times 6\text{in}\text{.}$ by 24 in.) on center wood frame, and steel stud framing. Additionally, structural insulated panels were modeled for the operational energy of the building. For each scenario, the designs were based on the minimum $R$ value required by the International Building Code. ATHENA, a life-cycle assessment software tool, and eQuest, an energy usage modeling software tool that calculated the operational energy of the building, were used to evaluate the environmental impacts of the building, during the construction, use, and end of life phases, for each scenario. The results show that in the preuse phase, the insulated concrete buildings produce the greatest impact on the environment followed by the concrete block, poured in-place concrete, and steel stud buildings. Traditional wood frames had the fewest environmental impacts when considering only the preuse phase. In the use phase, the insulated concrete buildings had the lowest impacts to the environment because they required less operational energy, whereas concrete block, poured in-place concrete, traditional $0.05\text{m}\times 0.15\text{m}$ by 0.6 m ( $2\text{in}\text{.}\times 6\text{in}\text{.}$ by 24 in.) on center wood frame, traditional $0.05\text{m}\times 0.1\text{m}$ by 0.4 m ( $2\text{in}\text{.}\times 4\text{in}\text{.}$ by 16 in.) on center wood frame, and steel stud framing had progressively larger environmental impacts. The end of life phase was negligible with respect to the other phases. In the complete life-cycle assessment (LCA), 50-year life span, insulated concrete exterior walls used around 700 GJ (5%) less energy than traditional wood $0.05\text{m}\times 0.15\text{m}$ by 0.6 m ( $2\text{in}\text{.}\times 6\text{in}\text{.}$ by 24 in.) on center wall systems. The results also indicate the importance of exterior wall’s thermal mass for the energy performance of a building, especially for a city located in a hot climate zone such as Phoenix, Arizona, and the importance of a holistic approach, such as LCA, to properly assess the negative environmental impact of different technologies.