how far apart should joists be on a deck?
The maximum distance a deck joist can span between supports is determined by the joist's dimensions and species, as well as the spacing between joists. The closer the joists are to each other, the greater the distance they're able to span safely. Two-by-twelve Douglas Fir joists spaced 12 inches apart on center, for example, can span 20 feet, 7 inches, but the same joists spaced 24 inches part can only span 14 feet, 7 inches. Cantilever.