Abstract: A multi-story building is constructed by first erecting at least one modular stairwell tower on a concrete base pad. The tower includes a number of horizontally alternating precast concrete modular stairwell units arranged in a stack and corresponding to twice the number of floors in the building. Each stairwell unit includes a precast reinforced concrete tower section having opposite side walls and opposite end walls defining an open top and an open bottom and a height generally equal to one half the vertical distance between two adjacent floors. An inclined stairway and a horizontal landing platform are formed within each tower section and are rigidly connected to the walls. Anchor members are embedded in the base pad and in upper and lower portions of the walls of each tower section, and adjacent anchor members are connected by weld plates. Each stairwell unit has a handrail supported by the corresponding stairway.