Windowsills can be added to existing windows in the drawing. Once the window is in place, follow these steps:

1. Go to the Wall Drawing tab and pick the Windowsill tool:
   
   
   
   
2. Move the cursor to an existing window in the drawing area. The sill snaps to the window.
3. Click the sill to attach it.
   
   

After you have placed a windowsill, you can still change its length, depth and other values by selecting it in the drawing and changing settings in the quick properties box that appears.

You can remove a windowsill by clicking the yellow, cone-shaped snap point shown at the component’s top edge in 3D view.