## 2 Materials and Methods
### Cycle Analysis  
The life cycle analysis is an objective process that allows for an evaluation of the environmental quality of a product or service in a global way, focusing on studying the environmental aspects and potential impacts in the stages of its corresponding life cycle: the acquisition of raw materials, production, use, and final disposal [22]. It is a timely environmental tool to quantify the true impact of the construction of buildings since it is based on objectively studying the different environmental impacts and allows the use of software to evaluate and encompass all the different processes involved, analyzing in-depth the environmental behavior of the inputs (energy, raw materials, and water used) and outputs (general waste and emissions transmitted to the atmosphere) [23]. For the environmental impact assessment, a life cycle analysis (LCA) will be carried out based on the standards ISO 14040 [24] (\"Environmental management. Life cycle assessment. Principles and framework\") and ISO 14044 [25] (\"Environmental management. Life cycle assessment. Requirements and guidelines\"). In addition, it consists of 4 fundamental phases:  
* Definition of the Objective and Scope: The objectives were to quantify the environmental impacts associated with the production phase (which includes the supply of raw materials, transport, and manufacturing) and the construction phase (which includes transport and construction/installation processes) of a two-story single-family house with an area of 42 m\({}^{2}\) and identify the alternative (masonry with conventional and aerated autoclaved concrete blocks) that contributes to a lesser extent to the impact categories considered. The system's limits are defined in the EN 15804 standard [26]. The construction of the house comprises processes that consider all the elements, raw materials, and components that comprise it. Therefore, they are affected by the flows of matter and energy during their useful life. For the limits of the system that were considered in this project, two phases can be distinguished (Figure 6): the production phase and the construction phase. The first phase includes the supply of raw materials, transportation, and manufacturing; on the other hand, the construction phase includes transportation and the construction/installation process [27]. * Life Cycle Inventory Analysis: Databases provided by Ecoinvent 3.6 (Table 4) were used to establish input and output flows (Table 5), taking as reference the diagram of the system limits (Figure 6). Additionally, the database of a study carried out on the analysis of the life cycle of clinker, cement, and concrete in Ecuador, and of electricity, was used [28] (which includes all types of power plants that are in the country considering the national energy balance of 2018 [29]). The quantities and the transport to the construction site of the materials corresponding to the construction of the gray work of the structure (such as formwork, reinforcing steel, concrete, and blocks) were calculated. Other necessary data were taken from the available inventory, carried out in 2017, of the construction of a host located in Lima, Peru. In this analysis, it was assumed that 1.39 kWh/m\({}^{3}\) of diesel, 0.30 kWh/m\({}^{3}\) of electricity, [30] and 0.5 kL/m\({}^{2}\) of water [31] are necessary for the construction of a building. The data was recalculated for a construction area of 42 m\({}^{2}\) (Table 5).