Intersection groups are simple index numbers stored with every joinable element (walls, roofs, …). Only elements that share this number are joined/intersected.
Kind of essential, actually, and still missing in VisualArq - should a roof or a beam join a wall? Should (overlapping) walls join?
I learned ArchiCAD recently, where this feature came in handy, simply and elegantly.
Btw.: ‘Intersection Groups’ are a per-layer-property there. Maybe better if they were a per-object-property.
We had this discussion before last year already. Time flies, and this project is still on the table, and that facade problem still lingers…