Legal bedroom? - Chicago

[Kevin O'Brien]

Hi, I'm a newer investor hoping to get clarification on legal bedrooms in Chicago. Background: I'm negotiating on a multifamily in Chicago (3/1's on 1st & 2nd floors, 2/1 in garden). The tax docs list as a 2-unit but the owners + seller's agent insist they have zoning compliance paperwork that it's a 3-unit - our offer has a contingency on getting the zoning paperwork for a 3 unit.

My question is related to the garden unit - what constitutes a legal bedroom? The unit appears to be legal - 8' ceilings, kitchen, bathroom, living room and 2 bedrooms. There are 2 methods of egress directly to outside  - front door (in living room) and back door (in hallway/mudroom). 

However, the neither of the bedrooms have windows...are these bedrooms (and therefore, unit) legal?