Hi!
I have a situation where I have a foundation slab that sits in the same level as the floor (it is for some machines). There is a structural column that has a base level 150mm lower than the top of the foundation, and the foundation drops down and attaches to the bottom of the column. I can`t seem to get rid of this, neither with detatch nor unjoin. The foundation is a family that I have created myself, and I have even made it with no geometry "touching" the column.