James has the right of it.  These spacings - including 12" - get used for a
variety of things.  16" happens to yield a solid enough structure while
still maintaining 8' spaces.  In floor framing I've had to deal with 12",
16", 19.2" and 24".  In roof framing I've also dealt with 48" and 96".

-Ken

On Thursday, April 17, 2014, James Thompson  wrote:

>
> On Apr 17, 2014, at 4:55 AM, Scott Garrison wrote:
> >
> > But never having thought about it  - only built many structures to this
> > requirement - it begs the question where did 16" come from? Why not 12"?
> I
> > understand that railroad tracks in 2014 are sized to Roman chariots of
> > likely 500 BC - so that's where that standard came from. But if we framed
> > to 12, 18, or 24 inch all engineered beams and calculations would have
> > easily accommodated - spans et al would simply be different and plywood
> > might be sized differently though 48 x 96 is still easily and completely
> > divisible by all but 18.
> >
> > Completely useless question but I find myself intrigued nonetheless by
> the
> > answer. And it isn't just "Because"
>
> My thinking is that sheet goods are made 4 feet wide, and 3 times 16 is
> 48. Thus the sheet goods do not require trimming to fit framing on 16"
> centers.
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