Should a 20- by 20-foot garage floor slab be jointed? Many recommendations for contraction joints allow spacings of 15 to 25 feet.
The thin slabs commonly used in residential garage floors are likely to crack if not jointed at small intervals of about 10 feet. Whenever possible the joints should be located to produce panels that are square or nearly so. In this case the floor should obviously have one joint across the floor in each direction to produce four 10-foot-square panels. It is quite possible that without jointing the floor will remain intact for about a year but will finally crack.