Does a sub need to be on the floor?

I live on the top floor of a small apartment building.  A sub on the floor would be tough on my neighbors but no one lives above us.  Do people put subs on shelves? 

I don't listen to music all that loud.  Usually the loudest thing I listen to is TV/Entertainment.

And I'm not a huge bass head so I can't imagine ever even wanting a large sub.  Maybe a small 8" one.

I don't have new mains yet - I'm still shopping and so far and like the small bookshelf models (so far without subs) such as Sierra 2's.

Thx