I'm planning a replacement for my deck and ran into a question that I cannot find an answer to anywhere. Why does everyone place deck joists at either 16" or 24" OC (or sometimes 12"), but not 18" or 20" or 16.75" centers?
In my case, I have a setup where 24" centers would be within code, but I don't like the feeling of decking with joists that far apart. 16" centers are what I'm after, more or less, but that would leave me with a final space of about 4". Why not just space out the rest of the joists to 16 1/2" spacing and save a joist? I could leave a 20" space at the end, but again, why not space all of the boards evenly?
I can see why you wouldn't want to do this in an enclosed floor or wall inside a house, but for something like a deck where the framing is actually visible between the decking boards, why does it matter? Or does it matter?
To state the question(s) clearly: Are atypical, but regular, joist spacings within code? If so, why are they not used? If not, why not?