This project was carried out because of a need for increasing the production efficiency at SKANSKA Byggsystem. The current production takt is 20 modules per week which at first step should become 24 modules per week and in a second stage, 28 modules per week. In this regard, the lean approach is applied to modify the procedures the production processes are based on. Value Stream Mapping is used as one of the lean tools to illustrate the total image of the operations and lead times. Although it is essential to consider both the production and administrative procedures in analysis and implementing Lean tools, in this project the focus is on production operations and material flow rather than the information flow. In the empirical study, different production areas in the factory are considered and the material flow is described from storage of raw material until storage of finished modules. The empirical study has resulted in a description of the current situation of the factory and current value Stream Map is drawn based on that. In the analysis part, different areas of waste in the production stages are defined and modifications for eliminating waste and increasing efficiency are suggested; having the main criterion of enabling the production to produce 28 modules per week, these changes have resulted in a future state Value Stream Map of the factory. In addition, modifications regarding the factory layout and outsourcing strategy are described as well. Finally, it is discussed that with minor changes it is possible to produce 24 modules per week. It is shown that by keeping the same resources and production methods, it is impossible to have 28 modules per week, although, outsourcing the bathroom module results in a great improvement, however this is not enough for providing required extra capacity. The most applicable approach is to implement the changes and improve the production procedures to get to the maximum available capacity and add extra resources to provide the required capacity of 28 modules per week.