To combine panels in a curtain wall, remove curtain grid segments. 
 Video: Place Curtain Grids
 Video: Place Curtain Grids 
-  Create a curtain wall with grids. 
- Select a curtain grid. 
- Click Modify | Curtain Wall Grids tab Curtain Grid panel Curtain Grid panel Add/Remove Segments. Add/Remove Segments.
- Click on a curtain grid segment to remove it. 
  As you remove segments, adjacent panels join. 
   
- Click in white space in the drawing area.