How Far Can A 12x12 Beam Span. A double 2x12 beam can span 12 feet; For instance, joists that are placed 24 inches apart must be wider than joists placed 16 inches apart.
The width of a joist/beam is not nearly as important as the depth. Much of what the width is doing is keeping the beam from rolling sideways (why a 2x12 that is only 1.5 wide can span 16'). Half way down the 16' wall i would triple 2x12's again across the 18' direction and then using simpson hangers set my 2x12 joists perpendicular to the tripled 2x12's.
When supporting joists that span 12 feet with no overhang beyond the beam, a double ply beam can span in feet a value equal to its depth in inches.
This is where i have my open span. Beam span calculator grayson county residential wood deck construction strategies for safe affordable decks jlc deck. I had planned to triple 2x12's (rather than 6x's for ease of handling) for my header across this span. On longer spans the beam may require much more bearing space as indicated by this table.
