Then there's your HVAC ductwork that's been contaminated, circulating that crap. 

Crawlspace completely covered in water, couldn’t see past the opening without crawling inside as there was plastic hanging down, structural supports not properly installed, ductwork not attached to the HVAC system literally laying in the water, the roof is literally not even attached at one of the joists where it should be attached to the house, and wiring chewed through in the attic of the garageI feel those are items worth negotiating on right?

It was close to 2 years before they installed duct work to the vents and a year before a AC UNIT was installed.

I want to separate the utilities so they're paid by the tenants each month, I've gotten quotes to separate the existing furnace from the ductwork and add in a second furnace (10K).

The only way to control each apt is to have controlled dampeners in the ductwork .

I'm also experimenting on a build right now and exposing the ceiling joists on the first level as well as the ductwork.

If it's on the duct work typically people just encapsulate it so that it can't be disturbed and it's the most cost-effective and easy method.

No ductwork needed, and it supplies heat and AC.  

Central air/heat duct-work.

[It is currently empty] Both units have a space for a small stackable washer/dryer BUT there are no dryer ducts/exhausts/vent AND in the upstairs unit the plug would need replaced [it doesn't work and the inspector doesn't know why]I don't plan to buy washer and dryer because of the other expenses we already have [new flooring, plug for downstairs stove, need downstairs appliances] putting us near the top of what we can spend right now, but if I put in the new plug and ductwork, they could potentially buy their own.This is not a high rent area [think 05, 09, 13], but what do you think the positive/negative impact on rents would be to either: a) not repairing plug or adding vent and saying, "Sorry, no washer/dryer" or b) repairing it so they have the option if THEY want to spend the money.I would love to do it just to make my units nicer, but I have to be cognizant of what I'm currently spending.