Improving labor productivity of in situ reinforced concrete construction is necessary because of the importance of this material to the industry. Several factors influence labor productivity, but buildability is among the most important. Despite the plethora of research into construction productivity reported over the years, a thorough examination of the literature revealed a dearth of research into the effects of buildability factors on the efficiency of the concreting operation. Because concreting is an integral, labor intensive, trade of in situ reinforced concrete construction, the objective of this research is to explore the influence of primary buildability factors on concreting labor productivity. In achieving this objective, a sufficiently large volume of productivity data was collected and analyzed by using the categorical-regression method. As a result, the effects and relative influence of: (1) concrete workability; (2) reinforcing steel congestion; (3) volume of pours; and (4) height relative to ground level, on labor productivity of skipped and pumped placement methods are determined and quantified. The findings show significant impacts of factors investigated on the efficiency of the concreting operation, which can provide designers with feedback on how well their designs consider the requirements of the buildability concept, and the tangible consequences of their decisions on the productivity of the operatives. Practical recommendations, moreover, are presented, which upon implementations, may improve the buildability level of this trade, thus translate into higher labor productivity and lower labor cost. On the other hand, the depicted patterns of results can provide guidance to construction managers for effective planning and efficient labor and plant utilization. - See more at: http://ascelibrary.org/doi/abs/10.1061/(ASCE)CO.1943-7862.0000404#sthash.tMVx7R55.dpuf