There has been significant moisture intrusion around windows and thru roof leaks.

With an older building you may also want to assess risks of water intrusion in the basement, old wiring, old water mains, and old sewer lines.   

The problem persisted, so we  pressure tested all the lines in the house (found two leaky valves - under 100 PSI - but nothing to explain the increased water consumption).Then we found the cause - a disgruntled tenant (who was moving at the end of his lease) who would come home in the evening and leave the bathtub spigot running for an extended period of time (another tenant ratted him out as they were tired of all our intrusions while looking for the problem).  

I had a couple minor bowing of old brick foundations and some minor water intrusion also.  

There had been water intrusion through the walls which resulted in a variety of molds.  

;)https://homes.yahoo.com/news/experts-rent-control-causes-more-problems-solves-181219436.htmlRising rents nationwide are causing rent control to gain traction — but not among economists, real estate analysts and other housing experts.A whopping 63 percent of experts surveyed for the Zillow Home Price Expectations Survey (ZHPE) said rent control ordinances are “government intrusions into the marketplace that, however well-intentioned, always create more problems than they solve.”It’s unusual for such a large group to agree on a single answer, according to Terry Loebs, founder of Pulsenomics LLC, which developed the Zillow-sponsored survey.

One issue is that the hearing impaired gentleman can come off as intrusive and has been too forward in trying to get female tenants attention.

I don't look at doing these things as intrusive at all; it's my investment and I'm entitled to protect it, plus my lease spells out that I will be doing so.

The interlocking type can be taken up and moved if necessary, so if there was water intrusion at some point or a need to get to the subfloor if would be fairly easy to do so.

Look out for water intrusion in the basements which can be an issue in much of the midwest.