I have seen many pictures on here of open beam ceilings. What is typically used then for the 2nd floor if the beams that become the joists are spaced much further apart then the typical 16" center joists and plywood for a floor??
T&G 2x6's are a common choice. They could span as much as 4' for a loft or bedroom, but closer beam spacing might be preferable for a real solid floor. We just used 2x8 framing lumber with splines between.