That makes it 3 full foundations high instead of one and a half. That's a heck of a lot of vertical space. Most of my factories have 3.5 foundations in between the floor and the ceiling. That leaves absolutely no space for anything else, so it's just not a practical solution no matter how you look at it. Mind you, 3.5 is still quite tall compared to a lot of pictures that I've seen from other players. Most seem to go to the bare minimum of 2.5 foundations.