## 2 Research Method
### Identifying Lean Tools in the Building Project Design Process  
To identify Lean Construction tools applied during the design phase of building projects, a systematic literature review was conducted, following a methodological procedure structured in three main stages: search, filtering, and validation. First, an exhaustive search was carried out in the Scopus database, selected for its international recognition  
Figure 1: Research method. and broad coverage in engineering and technology [22]. The search was guided by the keywords \"Lean Construction\" and \"Tools\", resulting in a preliminary sample of 49 documents. Subsequently, two inclusion/exclusion criteria were applied. The first criterion consisted of a temporal filter, considering only documents published between 2013 and 2023, which reduced the sample to 43 articles. The second criterion involved a manual screening process, selecting only those documents that included explicit tables or listings of Lean tools applied to design. This stage narrowed the sample down to four articles. As a complement, conference papers from the International Group for Lean Construction (IGLC) were reviewed using the same filters, yielding one additional document. Lastly, the academic thesis titled \"Integration of Overlapped Design and Construction Stages Through Location-Based Planning Tools\" was incorporated, resulting in a final sample of six documents for in-depth analysis. This sample served as the foundation for identifying Lean Construction tools used during the design phase and evaluating their functionalities and limitations in the context of building projects. In the second stage, the application of these tools according to project type was analyzed. A complementary literature search was performed using the Scopus, Web of Science, and IGLC databases, selected for their relevance to natural sciences, engineering, and English-language scholarly publications [23]. The search was guided by the equation \"Lean tools design and 'n'\", where 'n' corresponds to the iteration of each previously identified Lean design tool (see Figure 2). The final selection of documents was based on two inclusion criteria: (1) a ten-year publication window and (2) a manual review to identify studies that demonstrated practical applications or explicitly suggested the implementation of Lean tools in design processes. This search yielded a final sample of 26 documents for detailed analysis. Finally, an expert validation process was conducted to corroborate the relevance of the identified tools. A five-question survey was designed and distributed to 37 international experts in Lean Construction and building design. Given their geographical distribution, the validation was carried out online in two language versions: Spanish and English. The process was implemented in two phases: an initial pilot with three experts, followed by a broader application to 34 additional experts selected from the authors identified during the second literature review. As a result, 16 complete and valid responses were obtained and used to confirm the applicability of the Lean tools within the context of building design (see Table 1). Figure 2: Complementary literature search flow. The five validation questions were designed to address aspects ranging from general to specific, aiming to assess the experts' level of knowledge and experience regarding Lean tools. These questions sought to determine the following: (i) The general knowledge experts had about the tool. (ii) Have they previously read about the tool? (iii) Did they know of any case studies where the tool had been applied? (iv) Have they implemented the tool in any building design process? (v) The extent to which they would recommend using the tool. Additionally, experts were asked to propose other Lean tools that could be applied to the building design process. Only tools suggested by at least two experts were considered, and four additional tools beyond those found in the literature review were identified.