On the construction side
- two egress regardless of sqft due to height above grade
- Joist size will likely be your biggest cost factor. Older homes here typically have 2x6 or 2x8 attic floor joists. In a typical Chicago house these do NOT meet load requirements due to span. New 2x10,12 joists will be needed
- all light, vent, electrical, plumbing and heating requirements will need to be met for a legal unit
- Another significant factor to consider is how much actual floor space will remain after you meet kneewall height requirements. This tends to take away a lot of space.
You may want to consider hiring an inspector or architect to provide a feasibility report.
A few things that may come up:
1. Two methods of entry and egress.
2. Parking restrictions
3. Floor Area Ratio Requirements
4. Mechanical Systems Upgrade
5. Attic Floor Structure.
Best of Luck
Keller Williams CCG