QUOTE (dwb @ Mar 10 2010, 02:14 PM) Does anyone have any experience with hiring contractors to lower the basement floor (via jackhammers) to allow the basement of a rental building to be renovated (and thus rented for extra income)? Any feedback would be appreciated, just trying to get an idea...

Sounds like this person is trespassing. You could threaten to call police and have him charged with said offense if he does not leave immediately.