half wall underneath doorway

[JoAnn]

You really should take a look at at all the help offered at HomeDesignerSoftware.com

Listed under support/help database. In particular under categories/DOORS/Placing a Railing in a Doorway.
A railing made solid is merely a half wall.
This is your solution.

The sample pic you showed is a very poor example by homedesigner. It only tells how to create the wall, and then does NOT explain how to place it in a doorway, as they show.