A couple of years ago when I was building my deck, I soon realized that 16’ 5/4 boards don’t lay down anywhere near straight over that long a run.
My fix was to make an oak wedge about 2’ long and secure a pipe clamp to the rafter about two inches away from the 5/4 and stick the wedge in the gap and hammer it until the 5/4 board was straight.
How do you all lay those boards?
-- Mom always said, "you can do anything you put your mind to." The older I get the more I realize she was right.