I am not clear about your question but one think I can tell that you taken structural "Wall Foundation" which can be placed only by picking any wall, and it is very normal that "Wall Foundation" have no Avatar.
You said that "Foundation wall"- that means its a wall, but you taken "Wall Foundation", this is totally different. if you want to place the "Wall Foundation" then pick your desire wall, "Wall Foundation" will placed bottom of the desire wall.