Walls and Curtain Walls - Autodesk Revit Architecture 2015 Essentials - page 39

Options Bar setting is correct for Top or Base. Now select the wall
with the profile that you just edited. This attaches the top of the
thicker wall to the underside of the upper wall, as shown on the right
side of the figure.
FigUre 2.14 Attach Top/Base setting
The great thing about this technique is that the relationships
between the two walls are maintained if you edit the elevation profile
of the upper wall. Performing these steps is a lot faster than hav-
ing to edit the elevation profile of both walls! If you should need to
detach the lower wall, follow the remaining steps in this exercise.
4. Select Generic 12″ Masonry and click Detach Top/Base on the
ribbon.
5. Click the Generic 8″ wall above, or click Detach All on the ribbon to
reset the wall back to the original 2′-0″ unconnected height.