## 2 Difference Between LCA of Buildings and LCA of Neighborhoods
### LCA of Neighborhoods  
Recently, the focus has been shifted in focus from the building to the entire urban area to understand the potential impacts of a population's activities. Sustainable practices can be implemented at the neighborhood level because neighborhoods offer a good balance in size. They are large enough to address broader issues that go beyond individual buildings yet small enough to allow practical actions to be taken and monitored effectively [29].  
The methodology of neighborhood LCAs involves analyzing not only the buildings within a neighborhood but also their interaction with each other and with surrounding components, such as public networks, public spaces, and the mobility sector [6; 28].  
Neighborhoods, being complex and dynamic systems, can present challenges in the environmental evaluation of their components. This is primarily due to variations in functional units and system boundaries (spatial aspects), as well as temporal variations within each neighborhood [30]. The system boundary significantly affects the results of LCAs on an urban scale, with implications for study outcomes [26].  
Two studies have specifically focused on the effect of road infrastructure on the environment [31; 32]. On the other hand, other researchers also consider the effect of mobility [29; 33]. For a comprehensive analysis of the urban scale, all the different components mentioned above must be included, which is the case in several studies [3; 34]. The aforementioned variables represent the spatial aspect of the study.  
Besides the system boundaries of the neighborhood, additional temporal and behavioral parameters can also affect the results of the study, increasing uncertainties, and thus must be considered. The most important factor that needs to be studied is the behavior of the residents of the neighborhood. Not all residents consume the same amount of energy and heat, nor do they all recycle with the same proportions or commute the same distances within the limits of a neighborhood [35; 36]. A second factor that should be studied is the difference in energy mixes and future emission intensity of electricity, which are expected to change and become more sustainable going forward [26]. Finally, the ever-increasing climate change and the variability in the climatic conditions will affect the heating and cooling demand of the population. A reduction in the heating demand is certain due to the forecasted increase in global temperature and consequently an increase in the cooling demand [26]. Usually, to analyze the effects of such parameters, sensitivity and contribution analyses are required and conducted because these factors are unpredictable and dynamic within a neighborhood.  
The life cycle assessment of neighborhoods has the advantage of being able to analyze the environmental impacts of various urban projects, such as the construction of new buildings, the demolition of existing lots, and the development of new urban areas [6; 20].  
However, comparing neighborhood life cycle assessment studies can be challenging due to the numerous factors that need to be considered. The different plans and structures of urban areas make it difficult to establish uniform working hypotheses. A calculation hypothesis that works in one region may not be applicable in another region [11]. Figure 1 illustrates the differences between the components of a building LCA and a neighborhood LCA.