While teaching an ADT class today, I was asked what is the best way to draw spread footings using ADT. My first thought was to use slabs, and size them accordingly. But after looking at it more closely when I got back to my hotel, I believe the easiest way to draw spread footings is with the wall command.
There are several wall styles that ship with ADT that indicate a footing below the baseline of the wall. They are located in the wall style drawings in the content folder. The settings are able to be edited through style manager. You can adjust the components to the desired widths and use the offset options to reach the required depth. The styles that ship with ADT have a component that is called footing, that has the concrete material applied to it, and it is drawn on a footing layer that has a hidden linetype. This is a quick and easy way to indicate footings below structural walls.
Below is a CMU-12 Concrete-12x24-footing wall style that shows the footing below as a hidden line. The components do show up well when you cut a section through it. If you simply need a footing without a wall, you can copy the wall style and delete the cmu component in style manager. This should help when you are trying to indicate footings below walls.