Life Cycle Assessment
On this Project:
Can Aktas
PhD
Residential building lifetime data that presents existing trends in the U.S. was analyzed. Results indicate that residential building lifetime in the U.S. is currently 61 years. Existing LCAs rely heavily on estimates for residential building lifetime, and choices are usually made arbitrarily. This study is the first time mean residential building lifetime has been calculated from a large, reliable sample and used in LCA.
Lifetime of buildings and products presented in the current study should not be taken as static values. Future trends, occupant behavior, population demographics, regulatory policies, or development of new technologies have the potential to alter both lifetime and emissions of buildings and building products. The increasing trend in the age of demolished residential buildings was demonstrated in the current study. Ranges of values supported by statistical analysis were used throughout the study to compensate for some of the uncertainties associated with variables. The use of distributions that are based on past reported values, instead of deterministic values chosen arbitrarily for lifetime of buildings and building products improves the objectivity of a life cycle study that assumes average conditions when project specific data are not available. More data on environmental emissions of interior finishes is also a necessary step towards more robust results.
Interior renovation energy consumption for the residential model that was developed by using average U.S. conditions was found to have a mean of 220 GJ over the life cycle of the model. Using published data on energy consumption during pre-use and use phase of residential buildings enabled comparisons to be made among interior renovation impacts and other life cycle phases. Ratio of interior renovation to pre-use energy consumption was calculated to have a mean of 34% for a model regular home and 22% for a low-energy home. Ratio of interior renovation to life cycle energy consumption of residential buildings was calculated to have a mean of 3.9% for a model regular home and 7.6% for a low-energy home.
Life cycle impacts of regular buildings are dominated by use phase emissions. However, this is likely to change as buildings become more energy efficient during their use phase. An increase in the number of low-energy buildings would decrease the use phase emissions of residential buildings, increasing the relative importance of interior renovation over the life cycle of a residential building. Such an increase would necessitate more focus on interior finishes in a building LCA.
Due to its influence on product lifetime and emissions, the effects of consumer behavior related to interior finishes needs to be better quantified in order to improve accuracy of residential building LCA. Since lifetime information plays an important role in life cycle studies, and since consumer behavior can greatly influence product lifetime, developing a model that can accurately predict product lifetime by including the effects of technical factors as well as consumer behavior becomes a necessity. Such a tool would not only improve the accuracy of building LCA studies, but also of product comparison studies as well.
Without fully understanding and quantifying the underlying problems, it is not possible to develop effective environmental impact reducing strategies for the built environment. While collecting data for product lifetime, it was noticed that a product’s actual lifetime was usually different than what the product was designed for, and was determined by the effects of consumer behavior. Therefore, studying the supply chain from the initial design phase down to individual consumer preferences could open new opportunities to reduce the environmental footprint of products and still maintain economy.
Aktas, C.B., Bilec, M.M.* (2012). “Service Life Predication of Residential Interior Finishes for Life Cycle Assessment.” International Journal of Life Cycle Assessment, 17(3), 362-371. https://doi.org/10.1007/s11367-011-0367-6
Aktas, C.B., Bilec, M.M.* (2012). “Impact of Lifetime on U.S. Residential Building LCA Results.” International Journal of Life Cycle Assessment, 17(3), 337-349. https://doi.org/10.1007/s11367-011-0363-x