Process for splitting one lot into two lots

[Chris Scales]

I'm looking at a potential deal in Chicago for a 3 flat on an extra wide lot. Half of the lot is empty and the empty half alone measures approximately 25x125. Based on comparable properties in the area, it seems like the 3 flat  is listed fairly competitively and the extra large lot is essentially an added bonus. Although, this is a pretty appealing deal regardless, it becomes extra enticing if I was able to split the lot into two lots and build a 2 flat on the empty lot (based on a quick look at the zoning (RS3) for this area, I believe this is possible).

Does anyone have experience with costs/process/timeline associated with this?

Thanks in advance!