Rats end up gnawing on the insulation of older homes.In this property class, it's vacancy and turnover that will kill you.

Cost will depend on a lot of factors: size of the units, how many head units are needed, how well air sealed and insulated they are, window placement and efficiency, difficulty of electrical and running the lines.

See: https://www.cookcountyil.gov/content/just-housing-amendment-human-rights-ordinance- Schedule your free ComEd energy assessment and get free areators, insulation, smart power strips, water saving showheads, etc.

Needs new elec, plumbing, HVAC, siding, windows, insulation/Sheetrock/Trim, Kitchen/Bathroom remodel.

The basement has already been sectioned off and with a little drywall and insulation, this will make a nice family-room.

Replaced everything, tore out the 1960's insulation (rockwool not asbestos), drywalled, and replaced and refinished the floor.

get good sound insulation

But if it's not working in tandem with the insulation, you'll find yourselves spending a ton on utilities during the hot and cold seasons.EDIT- oh, also- congrats on getting under contract. :-). 

You better hope you get really good insulation or you will be hearing everything the person does in the ADU. 

If you need more protection then you should consider adding entities to insulate each asset.