To avoid getting burned in a dispute over slab tolerances, engineers and contractors need to know how design and construction decisions affect variations in slab dimensions and locations. The contractor is usually responsible for controlling deflections of formwork and shoring that occur during concrete placement. Many designers believe that cambering the beams is the key to achieving a nearly level floor. While this sounds easy, the trick is to determine the amount of beam camber (upward deflection) that will offset the deflection from the dead weight of the concrete slab. In spite of the inaccuracy of deflection estimates, engineers sometimes specify beam camber to accommodate part or all of the dead load deflection plus part of the live load deflection.
Even if the engineer doesn't specify a camber, it's possible for supporting beams to have a camber. Besides fabrication tolerances, there are other sources of unintentional camber. The afternoon sun has been known to camber both steel and concrete members as much as 1 inch. Because of the amount of planning, the construction delays, and the cost of shoring, most designers prefer to use unshored construction if possible. A shoring system, though, controls deflection more accurately than cambering does. Shoring makes sense when excessive deflection requires enough extra concrete to substantially increase material costs.