A stair assembly includes at least one joist comprising an upper wall, a first lateral wall extending from the upper wall, and a second lateral wall extending from the upper wall. At least one stair step support bracket includes a tray support wall, a first side wall extending from the tray support wall, and a second side wall extending from the tray support wall. The first and second side walls define a pair of first front aligned positioning holes configured to receive a first set pin and a pair of first rear aligned positioning holes configured to receive a second set pin. The pairs of first front and rear aligned positioning holes disposed such that when the first and second set pins received therethrough contact the upper wall of the at least one joist, the tray support wall is positioned at a first rise dimension.