Coach House / Detached Garage Uses

[Brookes May]

I'm looking for input on what is legal for an existing coach house / detached garage within the city limits of Chicago. I've heard many differing viewpoints on how they can be used and Chicago building code seems to be vague on the subject. Specifically: 

1. Can tenants of the main building use the space for laundry and storage? 

2. Can there be running water or a sink or toilet? 

3. Can it be heated in the winter with a furnace? 

Basically, if nobody is LIVING in the space, can it be used for other, useful purposes that serve the occupants of the main building? 

Any advice here would be much-appreciated.