Schedule compression or acceleration is a common problem for specialty contractors. Schedule acceleration is often the result of late start, delays and/or added work. Generally, a contractor has three options in accelerating a construction schedule; scheduled overtime, increasing the number of workers, or creating an additional shift of workers. There has been a significant amount of research conducted on scheduled overtime on construction labor productivity. However, little information has been found in the literature addressing the cost implications or labor inefficiency associated with working a second shift. This paper quantifies the relationship between the length of shift work and labor efficiency. The results of the research show that shift work has the potential to be both beneficial and detrimental to the productivity of construction labor. The productivity loss obtained from the quantification model developed through this study range from -11% to 17% depending on the length of shift work used.