A modular system has been developed for construction of buildings using four components that may be either site-cast or factory precast. Assembly can be accomplished with a minimum amount of labor after proper but brief instruction. Buildings of 30 stories may be built with elements of standard design, but with slight modifications buildings of at least 50 stories could be built. The system is proposed for use in constructing offices, hospitals, apartments, hotels, schools, museums or warehouses. Four components are required, any of which can be varied to meet the building requirements. Service modules- these boxlike vertical loadbearing members are used to enclose kitchens, toilets, stairs, and mechanical systems risers. Beams- beams are of standard design and dimensions but length and depth can be adjusted to the requirements of the individual structure. Floor-roof members- T-sections, concrete plank or other components may be used, depending on performance requirements and economy or on plant precast types available. Wall panels- nonloadbearing precast concrete panels or panels or glass or other suitable material are used as enclosures. To make best use of the system ordinarily requires a building of at least 100,000 square feet or, if components are site-cast, possibly even more. The contractor can make his own forms. The system is sufficiently simple to be adaptable to local construction techniques and varying labor practices. The erection crew is made up of a crane operator and four men to position the components. Service modules are first set in place. A typical module for an apartment building is eight feet square and weighs 22,000 pounds. Notches in the side of the module fit over the edges of the panel to provide alignment. Floor members are finally positioned to compete each story.