There may well be a permanent shift in demand, David, but even if there isn't, it's likely to take a decade or so just to work through the temporary backlog in rental demand. Most new households don't move directly into either owner-occupied housing or detached housing, they rent apartments first. Calvin estimates the number of "shadow households"--meaning households that would ordinarily have formed but have not since 2006--at about 4 million. Here's a link to his research paper from 2012 (when the number of shadow households was only about 3 million): http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2048815.