A joist is supported at either end by either a beam, wall, or other framing member. They may also require additional supports, known as intermediate supports, along their length. Joist span is the distance between the beams, walls, or other structures that support a joist along its length.The total joist span is the distance from one end of the joist to the other. When sizing a joist or determining its span, builders must examine the design span rather than the total span.hey may also require additional supports, known as intermediate supports, along their length. Joist span is the distance between the beams, walls, or other structures that support a joist along its length. The total joist span is the distance from one end of the joist to the other.