From FreeCAD Documentation
- Create a normal Arch Wall, either by clicking two points of from an existing linear object
- Select the base object of the newly created arch wall
- Press the CurtainWall button, or press the C then W keys to create a curtain wall from the same baseline as the wall
- Make sure both the wall and curtain wall have the same Height
- Set the number of horizontal sections of the curtain wall to zero if you wish only vertical frames
- Set the desired horizontal mullion width and horizontal mullion height (or use a mullion profile)
- Prepare two (or more) materials, one for the panels, one for the void where the frame will be
- Make one multi-material, using one layer of the panel material, one layer of the void material with a negative width value (which will make it not drawn) corresponding to the vertical mullion height of the curtain wall, and another layer of panel material
- Attribute the multi-material to the wall
- Set the Host property of the curtain wall to the wall we created in first point