Chicago RS-3 Zoning question

[Dhru Das]

Hello all,

I am looking to purchase a 2 unit building in Chicago. The building seems to have an in-law garden unit with around 6.6 ft ceiling height. There is also an unfinished large attic area.

I have an option to dig down the ground and bring basement ceiling height to 7'6" and duplex down from 1st floor for large unit 1 and then duplex up for a large unit 2.

I have another option to try changing zoning from current RS3 to may be RT-4 or something so I can make the basement as legal after I dig the ground so building can be legal 3 unit.

The building is surrounded by B1-2 zoned building and it seems weird that only this building is RS-3. Does that help to try changing zoning for it or is it still very difficult to change zoning from RS-3 to a 3 unit building like RT4? Please see picture with the marker..Thanks!!