In the Wall Settings you can choose a different line type for your wall but you can't have that just apply to a structural drawing.
You could make Detail around the whole floor plan, then in the detail, treat it as a 2D background. Layout the Background seperate from but right on top of the Structrual Info in Plotmaker. Not ideal but...
There might a trick of putting the parts you want to show dashed on a false story below and having it show one story up.
HTH
David Pacifico, RA
AC27 iMac i9, 32 gig Ram, 8 gig video Ram