Are you running joists at 12ft length rather than 18ft? You'd end up using a lot more joists that way.
*A larger number of joists, not necessarily more wood, which could drive up the number of screws?
Good point. My napkin sketch has them at 12ft lengths, only because that feels right to me. 18ft lengths would (again, only in my mind) need more noggins, so could end up requiring more timber.
Are you running joists at 12ft length rather than 18ft? You'd end up using a lot more joists that way.
*A larger number of joists, not necessarily more wood, which could drive up the number of screws?