Yes,the limit is 4 up and 4 down, but if you use the foundation tool as a basement, you can make it 5 down. There is a trick if you like to build where you can do so in such a way that it looks like it is a lot higher. There is a tutorial, but it's on a site with mods, but just google "sims 3 9 livable levels" and you will find it.
Norma