I have a 10ft wall that spans only a third of the width of the house but is perpendicular to the 20' long 2x10s below it. One end of the wall could transfer load to the foundational wall but the rest is out over the joists with no columns or supports below. This 20' span has a beam 3' from the foundational wall and spans 15' to the next carry beam. Functionally, this wall could offer support for the floor (2x10 joists as well) of the dormer above but it only spans 2/3 the width of said dormer. It has no wall below nor directly above and the studs do not line up with any of the joists below. There's nothing special about the framing either, no double plates or studs. Any insight?
Yes, the new plan really helps. Let’s call North going up. So, I see the basement bearing walls/beams run East-West and is on the South side of the stairs.
So, 2x10 joists at 16” on center will support say live load (people and furniture) of 40 lbs. per square foot plus a dead load (framing, ducts, etc.) of 10 - 14 lbs. per square foot, depending on the species and grade of lumber. This is perfect for current Code compliance.
However, the joists in the 2nd floor sitting room appears to span much further than that if you remove the wall between the kitchen and dining room.
The risk to removing this wall is that the floor will sag and crack the ceiling in the kitchen and dining room...or worse, the 2x10’s are spliced over this wall and they will fail.
So, you’ll need to do a little more investigation. On the 2nd floor, what is the distance from the South wall of the stair to the South exterior wall?