Constructability is a concept with relative and not absolute value to increase optimization capacity of resources such as workforce, time, cost, quality, and working environment conditions. Given the growing complexity of projects and the increased number of failed and abandoned projects, the necessity to implement constructability in projects has become more tangible. Although the effects of lack of quantitative definition of constructability role in the traditional construction approaches are evident and have led to lack of coordination in performance of construction projects, so far no comprehensive quantitative approach has been considered to analyze the obstacles to constructability implementation. This study aims to identify and categorize the obstacles to facilitating the presence of contractors in the early stages of planning and design to implement constructability. In this study a comprehensive list of obstacles to constructability implementation is developed as a questionnaire. This questionnaire was presented to the experts, active in the field of construction. Finally, its results were analyzed using exploratory factor analysis method. Totally, 63 obstacles were questioned, then they were categorized by some of the experts of this industry into five categories of macro factors, including contractual, environmental, managerial, technical, and organizational. The significance of this study is due to this fact that identifying and categorizing the key obstacles to constructability implementation provides a useful reference for managers and owners of the construction industry to identify and develop solutions to resolve them. Identifying the obstacles to the presence of contractors in the planning and design stage and having a quantitative view toward this issue affects project implementability. In this regard, one can present more effective solutions to facilitate the presence of contractors in the early stages of design and also improves the effectiveness of constructability.

In fact, constructability is facilitating the construction of a project through integrating knowledge and experience to achieve the overall and common objectives of the project in all stages of it, but practically there is still a significant gap between design, construction, and achieving the desired project objectives. Studies show that separating the design and construction processes and lack of presence of the contractor in the design stage, prevent the effective use of experiences and specialty of the contractor to improve and develop design processes. This issue results in increasing project time and cost, poor relationships, and also increasing project waste and duplication. The barriers to implementing this concept can have major differences with each other in different locations all over the world, due to the unity of the executive conditions in various countries. This paper evaluates the existing practical barriers to implementation of constructability in the construction industry. A comprehensive literature review has been performed by the authors through using the Meta-Synthesis method and findings were used to form research assumptions. Three case studies of Mass Housing project (MHP) in Tehran were instigated. Outputs taken from nine interviews with different experts in this industry working in diverse areas, including owners, consultants and contractors are then ranked after theoretical saturation compared using the NVIVO Software and through pattern and descriptive analyses. The concept of constructability is focused on the early presence of contractors in the initial stages of the project. So that, through integrating knowledge and experience, problems due to lack of their presence in the early stages of the project can be reduced. Comparing the existing barriers to implementing constructability in Iran with those of the wider world, presents some effective solutions to facilitate the presence of the construction contractors in the early stages of projects.

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Despite allocating huge budgets to civil engineering projects, detailed planning, and employing human resources, project managers still face time, cost, and quality constraints. Most of these challenges are due to a lack of integration of different project phases and the limitations of the presence of construction and maintenance contractors in the initial stages of the project. Considering the benefits of applying constructability, operability, and maintainability (COM) concepts, many problems caused by lack of coordination, or duplications and weakness in management, and also time and extra costs due to lack of presence of construction and maintenance contractors in the early stages of the project are resolvable. In this regard, various studies have investigated the benefits of applying these concepts; however, there has been no comprehensive analysis of the benefits of COM. As a result of focus on the benefits of implementation of these concepts and evaluating the effect of each of these strategies and benefits, from different perspectives during various time periods, managers can increase project efficiency and productivity, and improve their performance, through using concepts and strategies of their implementation. This research aims to evaluate the trend of studies on the benefits of implementing constructability, operability, and maintainability in the construction industry. For that, the in-depth literature review method is applied. For qualitative analysis of the obtained information, descriptive analysis has been used. Then, the data was coded, and classified using Excel Software for quantitative data analysis. Finally, the charts presented were evaluated according to the classified fields of study. The necessity of performing such a study is significant because of the fact that a large share of a project's problems, such as lack of plans' integration and weakness of administrative system, and increasing time and cost, are due to lack of exchange of information and ineffective relationship between the design people and the construction and maintenance stakeholders, and ignoring the effects of design decisions on constructability and operability and maintainability implementation.