Hi, I have a question about a 2nd story I am adding. The house is currently one story. In the pictures, everything above the red lines on the left side, living room side, do not currently exist (yellow circle does not currently exist). I.e. currently all 4 red lines are the same height. I want to know about what happens to an interior wall (blue line) that becomes an exterior wall (yellow circle) on the second floor once I add it. Does the bottom floor wall that is 4.5" thick need to be thickened to support it? I plan to use siding and not rock for the exterior of the 2nd floor. The Red lines are extior walls, and the yellow circle is the 2nd floor of the interior wall that will be exterior at that height. Note that the room on the other side of that yellow circle wall is 17' ceilings, and there is no actual 2nd floor there.

If the answer is "yes, you must thicken the bottom part of the wall to hold the thicker top", How thick does that first floor interior wall (blue line) need to be?

Separate question, how thick does the second story wall need to be, from the outside to the inside?