Conducting life cycle assessments, or LCAs, involves many uncertainties, including those related to the factor of time. Time is very important in the environmental assessment of housing, because of the relatively long service life of houses. During a house’s service life many changes occur, which are not usually considered in today’s LCAs. Nevertheless this is of major importance in order to be able to make complete and accurate environmental assessments of housing. The aim of this article is to identify and classify the aspects belonging to the factor of time and to select solutions to handle these aspects in LCAs. On the one hand a difference is made between a static and a dynamic approach. On the other hand construction, demolition and frequency are distinguished. Six aspects of the factor of time resulted: design, production technology, re-design, waste treatment technology, technical service life and functional service life. So far only static factors are taken into account in LCAs, and only partly. To involve all the static aspects as well as to include the dynamic aspects, relationships between the six aspects of the factor of time have been defined and the most suitable solutions are assigned to the different groups of aspects, including scenarios, sensitivity analyses, turning points and potentials.
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