But why....?

[BucklesTrespen]

Anyone got tips for splitting the large house upstairs rooms into two rooms (or more) that doesn't involve bringing in the outer, windowed wall via partitions?

[ManuelBravo]

Not really, look around other homes and see what they did to give you ideas is the best advice I can suggest. You can be creative, however it really depends on what you have to work with.

[Claviusnex]

If you are looking to partition the room with doors your choices are limited to styles that probably won't match. Otherwise gaps between the partitions and/or using three with one screening the gap are the only ways I am aware of partitioning a room and accessing the partitioned area.

[Kittypryde]

On that wall, leave middle open with two pillars on sides of entrance. And blank walls on sides of pillars and open entrance to second room.

[Leloa]

I just placed one half partition in middle, bed on other side and "office" desk and room on the other. I did have the same problem so just did that...

[AriesMouse]

Pillars always make things look a little better, imo. If you line them up with the ceiling beams (at the cross section), it helps to keep everything looking lined up and neat, and they can often act as a guide for blocking out the space.