The Impact of Designer's Role in Involving Construction Personnel During the Design Phase on the Performance of Construction Project Schedule in IndonesiaThe study by The Business Roundtable's team in the US found that opportunities to reduce project costs and schedules by using existing and new construction technology are lost because construction too often is relegated to operate as a production function separated from financial planning, scheduling, and engineering or architectural design. Significant savings in both the costs and time required to complete the project can be accrued from careful interaction of planning, design, and engineering with construction into the creation of projects. The Construction Industry Institute's (CII) Task Force defines this term as Constructability, which is the optimum integration of construction knowledge and experience in planning, engineering, procurement, and field operations to achieve overall project objectives. By ignoring constructability in design, designer may be saddling the builder with possible construction problems that could lead to delays, inefficient use of resources, out of sequence work and others. This can be particularly troublesome which may have a devastating effect on project schedule and budget. Designer has an important role in building a receptive interface with construction personnel during the design phase. By communicating the design intent to the construction personnel, designer can gain the information he/she needs to improve the constructability of the project. This thesis study the role of designer in involving construction personnel during the design phase to improve the constructability of the project which leads to an improvement project time performance of construction project in Indonesia. A questionnaire survey was distributed to projects designers in Jakarta area. The data obtained was analyzed quantitatively to find the correlations and to make a regression between the role of designer in involving construction personnel during the design phase and the performance of construction project's schedule. The result of this research shows a positive, nonlinear correlation between the interface of designer with construction personnel during the design phase and schedule performance of the project. The main variables are: communicating the design intent to construction and the involving construction personnel from the construction contractor.