So if you put in an outlet so you can weld in your basement, it's now a multi-family?

The concrete slab will move and shift over time - concrete actually expands and contracts with temperature while porcelain and ceramic tile do not. 

I have (for our system) water and antifreeze temperature logger data collected every hour for the past several years.

The temperature in the Portland area in my opinion is that many people are trying to adjust but validate.

The hot water temperature was 140 degrees F at the time of testing.

Fall & Spring HVAC Service Target Date: April and October This service can aid in early detection of costly problems and save the cost of expensive, emergency service.A/C Service Includes: Check condenser coil, adjust operating pressures, monitor safety controls and starter capabilities, clean or replace filter, adjust blower components, calibrate thermostat, measure for proper temperature differences, clean condensate drain, tighten electrical connections, measure voltage and amperage on motors, lubricate moving parts.

Another solution may be to vent the attic space, if it is getting to hot up there and cool downstairs, that will cause humidity at the ceiling and  while your at it check the insulation in the attic, make sure there is enough to keep the temperature difference between the cooled space and the hot attic. hope one of these helps you.

You can add temperature and moisture sensors too. 

When I do call them my first idea is to call and assume they got my postcard (use this as a temperature gauge if they did/care), see if they have seen the property lately if they're not owner occupied, if they are ask how they've liked lately and then transition into seeing if they're open to selling it, what they expect for pricing and if it's within 10-15% of the price I'm willing to buy at then put in an offer, inspect it, tear it apart and then renegotiate at the number I'm comfortable at. 

It would work fine as adu the financing is the biggest thing, I personally have shipping containers as storage and with adding roofs and welding the containers to the foundation and adding perm electrical they still consider personal property.