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Upper Floors Upper floors are different. They are not on the ground. They must be held up by the structure. Often, they are made of wood or concrete. For a wooden floor, builders use joists. Joists are long wooden beams. They go from one wall to another, or from one beam to another. Workers put floorboards or sheets of wood on top of the joists. For concrete floors, they pour concrete onto a metal deck, with steel rebar inside for strength. CONVERSATION 2: Walking Upstairs Two workers are