One thing that helped me on 2 story structures was having a central firepit on the first floor with stone columns at each corner. These stone columns continued straight up through the second floor as well, so there was a central point that counted as "blue" stability (like the ground) all the way up.

Central firepits were an actual historic thing vikings did anyways.

The first floor has stone columns, and wood crossbracing near the ceiling that's so strong, the second floor was able to support another hearth in the center as well. So both rooms have a central firepits.