Precast producers can produce modular precast concrete units that include a roof, floor, front and back walls, and two side walls if desired. The modules' key benefit, in addition to the speed with which these “building blocks” can be erected on site, comes from the precast producer being able to outfit and finish the modules at the plant so they arrive at the site nearly complete.

Originally used for prison cells for many years, their use has been expanded for school classrooms, hotel and motel rooms, and other applications where relatively small, repetitive rooms are needed on a rapid schedule. Prison cell modules are the predominant method used for constructing justice facilities that include prisons and jails. These structures can be single or multi-level structures as high as 10 to 12 stories.