Removing Textures under buildings.

I wasn't able to come up with a satisfactory answer after searching the forums, so...

Anyone care to explain how to remove the texture under buildings. I've seen it done on various maps but alas, the answer escapes me :) . Whatever they did only takes effect after the game is loaded, not in the editor, so some guess can be made as to ho they did it.

Thanks in advance

Actually it is something done in the editor :)

Instead of using a building as a base unit, use a ward ^_^