20-1/8" Subfloor Height - things aren't adding up!

[clbpdx]

I'm at that point in my HD education where I'm trying to make sense of the relationships between Terrain Subfloor Height, Room Structure elevations and relative heights.

The default 20-1/8" above Terrain for (top of) subfloor is supposed to be the sum of:

 - 6" from terrain surface to SWT, or the white object in my attached cut-section view.

 - Floor structure (dimension "L" in diagram), or the 12-5/8" tall blue object in my cut-section view.

 

These two things add up to 18-5/8".  In my cut-section view, what happened to the missing 1-1/2" from the top of my blue object (12-5/8"), to the 20/18" from terrain to subfloor (red object)?

 

Hopefully I won't feel too dumb when somebody explains this to me ;-)

Thanks!

 

[Rookie65]

my guess is it's the sill plate?

[clbpdx]

Keith,

You were right, and that makes sense with 1.5" sill being standard.  The only way I could see and confirm this was by looking at it using Framing Overview and drawing more colored cylinder shapes.  See the attached - the white cylinder is 6" from Terrain to SWT, Red is your 1.5" tall sill plate, and blue is the 12-5/8" tall floor structure on top of the sill plate that gets us up to the top of the subfloor.

 

Thanks much!!!