Teh roof on # 4 was damaged March 15,2011 at 6:00 AM their time; http://www.tepco.co.jp/en/press/corp-com/release/11031504-e.html
As of this post it is March 16 7:17 AM their time, a whole day later.
The roof of the reactor is what they are talking about not the roof of the housing.