21 foot Tip and Roll 3 row portable school bleachers are made to roll in place. As school events change tip and roll bleachers go where they are needed on commercial casters. At 21 feet wide x 3 rows of 2 x 10 Aluminum Planks, this bleacher seats 42 adults and is only 30 inches high. This light weight bolted aluminum frame provides strong joints that will not develop weld cracks. The Rise is 7 inches per row which is comfortable for adults and children. Comes with a set of four no marring 5 inch casters with brakes preventing any markings on the floor and includes a wood sill to protect floors. NOTE: Please check your local building codes to determine required specifics for portable bleachers. Guardrails and additional foot boards are available.