In the last two decades, buffer-driven production strategies have been an emerging issue among lean construction researchers and practitioners alike. However, an in-depth understanding about the extent to which buffers impact system performance is still limited in construction, reducing the potential of using them to improve performance. To overcome this, the relationship between task-level labor productivity and buffer levels in a repetitive building project is investigated. In this research, a specific kind of inventory buffer is studied: work-in-process (WIP). A specific process was selected and analyzed in-detail as a case study to understand this relationship. The main result of this research indicates, through a linear regression, that an improvement in task-level labor productivity may be achieved when WIP buffer sizes greater than the size proposed by the lean ideal or the industry practice. However, this suggests a more in-depth investigation about the mechanisms operating in theory and practice in managing buffers in construction. Further research should focus on improving the analytical description of the relationship productivity/buffer on-site, as well as the understanding of the mechanisms at task and multiple task levels working in this relationship, and developing practical ways of using buffers to improve project-level performance.