## 1 Introduction  
Despite the critical role of the design phase, it is often overlooked and underdeveloped in many construction projects [1]. This phase is frequently characterized by ineffective communication, insufficient or inadequate documentation, poor information management, and limited coordination among the disciplines involved [1, 2, 3]. Additionally, decision-making during this phase tends to be erratic, further exacerbating coordination and collaboration issues [1, 2, 3]. Most changes at this stage stem from a lack of communication between designers [4]. Furthermore, designers' inadequately conceptualizing the final product often leads to modifications during construction to meet client expectations, resulting in inefficiencies and increased costs [5]. Traditional project management techniques have proven ineffective in addressing the complexity inherent in design management, as they assume that work can be divided and managed independently [1]. In fact, addressing design and construction issues requires a team-based approach [6; 7; 8; 9]. Previous research suggests that adopting a collaborative approach in the early design stages can mitigate many problems by promoting greater professional integration from the project's inception [10; 11]. Therefore, it is crucial for stakeholders and designers to consider the impact of communication flow, trust in shared information, coordination, and effective collaboration among architects, contractors, and subcontractors [4]. Lean Construction was introduced in the Construction industry to improve workflows, meet client requirements, and eliminate waste with increasing global adoption [12]. Lean Construction maximizes client value by eliminating non-value-adding activities, creating a reliable workflow, and pursuing continuous improvement [4; 12]. Although Lean Construction originates from Lean Production, its application in construction has required significant adaptations [12], leading to the development of specific tools and strategies [13]. Within this adaptation, Lean Design emerged as an approach focused on eliminating waste and non-value-adding activities in design processes [14; 15]. To address the challenges of the design phase, Lean Design has proven to be a key methodology, facilitating early client involvement, maximizing value, and identifying stakeholder needs and objectives to minimize rework and unnecessary tasks [16]. Although Lean principles have been applied to design management since the late 1990s [17], many studies have only examined a subset of Lean practices without fully exploring their applications in building design [3]. While some research has documented the application of Lean management principles and specific tools in design management [18; 19], the interactions between Lean tools such as the Last Planner System, Target Value Design, Set-Based Design, and Building Information Modeling (BIM) [14; 20; 21] have not been thoroughly investigated, nor have their combined benefits been extensively analyzed [4]. Currently, no studies explicitly identify Lean Design tools in building projects, nor do they systematically examine the functionalities, benefits, and limitations of Lean tools specifically applied to design. While this study provides a comprehensive identification and analysis of Lean tools for building design, it is limited by the number of expert responses obtained and the focus on tools with available literature and expert consensus. These constraints may affect the generalizability of certain findings and are discussed further in the concluding section. Therefore, this research aims to identify Lean tools in the building design process, compare their functionalities, and recognize their benefits and limitations within this phase. Therefore, this study not only addresses an underexplored area, Lean Design in building projects, but also contributes a systematic and validated framework that identifies, categorizes, and analyzes Lean tools specifically for the design phase.