**1. Introduction**

From the 1970s, a general awareness had been created with regard to environmental problems. The first oil crises, the end of the Thirty Glorious Years and the emergence of mass unemployment were highlights that questioned the idealistic aspect of a "model society", which had been in force since the end of the Second World War in Western countries. People were beginning to notice the incompatibility between the well-being of the productivity system, which is infinite growth, and the survival of the ecosystem as we knew it then. Thus, many people had come to believe that it would be beneficial for everyone to change the way our society operated [1]. Between 1960 and 1971, two large non-governmental organizations had emerged to fight for the protection of nature—Greenpeace and the World Wildlife Fund (WWF). The following year, that is, in 1972, the Club of Rome published its report under the tutelage of the globally respected Massachusetts Institute of Technology. They warned that the frenetic development of major industrialized nations would lead to the depletion of the world's reserves of non-renewable resources. Many environmental disasters that were publicized a lot more played an important role in this awareness [2]. The oil spills, Chernobyl, hurricane Katrina, or the heat

wave of 2003, which caused the death of 15,000 people in France, made their mark. At the beginning of the twenty-first century, a leap was made regarding the international awareness of environmental problems. The Communiqués of the United Nations Intergovernmental Panel on Climate Change (IPCC) were significant in making this happen [3].

These communiqués claim that humans are 90% responsible for the worsening of the greenhouse effect and that this could lead to a rise in water levels of more than 40 cm [4,5]. They point to the economic, environmental and social risks that global warming could create [6]. Even the Catholic Church has reacted by defining a new sin, the sin of pollution. Targets are set at the European level to address environmental issues. The 2030 Package fixed by all the member countries of the European Union revealed at least a 40% cut in greenhouse gas emissions (from 1990 levels); at least a 32% share in renewable energy; and at least a 32.5% improvement in energy efficiency. This objective can be reached if all these countries work in collaboration.

In industrialized countries, the construction sector is responsible for 42% of the final energy consumption [7,8], 35% of greenhouse gas emissions [9] and 50% of greenhouse gas emissions from extractions, from all the materials combined [6]. In addition, the urban sprawl is increasing land use, and between 1980 and 2000, the built space in Europe has increased by 20% [10]. Buildings are responsible for different types of soil consumption: a so-called primary consumption, that is to say, their building footprint; and also a secondary consumption, that is, the extraction, production, transportation and end-of-life treatment of construction products [11]. This type of impact is minimally considered in most studies, if at all considered. However, the life cycle analysis also studies the environment around the built area [12]. The culmination of all thermal and energy regulations is the European Zero Energy Building (nZEB) goal [13]. It aims to ensure that all new buildings have a neutral annual energy consumption; that is, they produce as much energy locally as they consume over the course of a year. This concept can be extended to the neighborhood scale to target the zero-energy level at the community scale [14].

A life cycle assessment is a method, an engineering tool, initially developed for industry. It aims to quantify the environmental impact generated by a product, a system or an activity. This requires an analysis of material consumptions, energy and emissions in the environment, throughout the life cycle [15]. An environmental impact is considered to be any potential effect on the natural environment, human health or the depletion of natural resources [1,16]. Thus, LCA is an objective process that allows for the establishment of various means to ensure increased respect for the environment [17]. Nowadays, a life cycle assessment (LCA) is the most reliable method for assessing environmental impacts associated with buildings and materials.

In 2002, Guinee et al. [18] stated that one of the first (unpublished) LCA studies on the analysis of aluminum cans was conducted by the Midwest Research Institute (MRI) for the Coca-Cola Company. Buyle et al. [19] showed that the first LCA in the construction sector was performed in the 1970s. In the early 1980s, life-cycle analysis widened its interest to the field of construction. Different studies used different methods, approaches and terminologies. There was a clear lack of scientific discussion and consultation on this subject [19]. In the 1990s, we saw many more multi-criteria approaches, such as environmental audits and assessments that studied the entire life cycle of products. These methods were beginning to get standardized; conferences were organized, and many more scientific publications were produced on the subject. From 1994, the International Organization for Standardization (ISO) was also involved in the field of life cycle analysis and in 1997 published, for the first time, its ISO 14040 and 14044 standards on the harmonization of procedures [20,21].

From the beginning of the twenty-first century, interest in LCA and reflections on the complete life cycle are increasing. Many more scientific studies are being published. Today, LCA is recognized as the most successful and objective multi-criteria assessment tool for environmental impacts, on the entire building scale [22,23]. In Belgium and several European countries, most of the studies on LCA in the construction sector concentrate on the building level [23–25].

In the literature, it is important to note that many studies on LCA have several limitations: some use a single scale when analyzing the reduction of the environmental footprint in the construction sector; others use only one indicator (energy demand) to conduct a study within a building; while others focus on a single stage of the life cycle (the occupation stage). To deepen this study, we carried out this work by pushing the reflection further. Thus, we will no longer work on the scale of a single building, such as many studies, but on the neighborhood scale. We will not study a single indicator, but more than ten. We will not focus on one step, but we will study the whole life cycle.

In Belgium, the first thermal regulation was born in Wallonia in 1985. The EPB Directive—European Directive "Energy Performance of Building Directive" (EPBD) (European Parliament, 2002) —has been applied in Belgium since 2008 and was regularly reinforced in the years that followed. It is important to note that European regulations have the merit of reducing the energy consumption of buildings during their occupation phase. However, they focus only on this phase. All other phases of the life cycle—the extraction of raw materials, production, choice of building materials, their transportation and even their recycling at the end of their life cycle—are not taken into account. Furthermore, the there is a lack of integration and following of different requirements, which is responsible for an asymmetry of compliance in the member countries of the EU.

Thus, our study has a goal to go beyond the occupation phase and take into account the complete life cycle. In addition, these regulations are interested in only one aspect, which is the consumption of energy. We want to study the set of different environmental impacts that are significant and known. Finally, the current studies on which the energy standards are based are often carried out only at the scale of the building. We want to broaden the reflection at the neighborhood level, as it is clear to us that the environmental issues of tomorrow will be resolved at the urban scale. We believe that this type of approach is the logical continuation of the current regulations and that it is important to take the plunge. It is thanks to this type of analysis, from the cradle to the grave, that one can judge the real and lasting aspect of a construction. Indeed, we can expect that the environmental cost of energy will decrease as well as the consumption in the building sector. As a result, the relative share of non-occupancy phases in the overall environmental balance will continue to increase.

This research proposes a more efficient method for analyzing the life cycle at the scale of a neighborhood, and compares the results obtained with those of other existing research. The design and analysis of several scenarios allow us to assess several important characteristics of the LCA applied to an eco-neighborhood.

### **2. A Review on Current Researches Regarding Life Cycle Analysis in the Building Sector**

The life cycle assessment (LCA) method is a clearly validated scientific method and is even standardized at the European level [20,21]. The LCA allows one to carry out different types of comparative studies [23], for example: (i) comparison of two entire systems or part of their life cycle; (ii) comparison between different phases of the cycle life; (iii) comparison of two different versions of the same system; and (iv) comparison of a system with a reference. The method also makes it possible to quantify an environmental impact on the complete life cycle of a product or only on one stage of the cycle without necessarily making a comparison. Thus, it is a tool that can not only serve as a decision aid, but also allows targeting of the phases of the life cycle of a product, which would need to be reworked with attention paid to the environment. The normative framework of the LCA [20,21] defines four different steps to follow: (1) the definition of the objective of the study; (2) the "Life Cycle Inventory" (LCI); (3) the "Life Cycle Impact Assessment" (LCIA); and (4) the interpretation of results—all these phases are organized independently and iteratively.

Specific standards were established for the LCA of the building sector by the European Committee for Standardization (CEN) in 2011: EN 15978 [26] and EN 15643-2 [27]. These standards are increasingly used to define and/or reduce the impacts of buildings on the environment. It is currently the only scientifically sound approach to carry out an environmental assessment at the building scale. It allows a quantitative study of the construction over their entire life cycle. However, its use at the urban or

neighborhood scale is recent [28,29]. Despite the novelty of the LCA application at the neighborhood level, it is considered the most reliable method. It is a challenge and a fascinating research topic to test the application of the LCA method to an eco-neighborhood, especially since no other study to our knowledge has focused on the comparison of so many parameters and environmental indicators at the community level. Note also that many sustainable building certification schemes are based on the LCAs of the building materials [30], such as BREEAM, DGNB and Valid in Belgium.
