Setback Encroachment & Rennovation

[Noah Lomax]

Hey Chicagoland BP-ers!

I'm currently working with a realtor to purchase a property that is completely distressed and will need significant rennovations inside (almost an entire gut; but not quite). Based on the property line, the existing structure is 10' over the setback line in the front. 

Before we purchase the property, I'd like to understand: when we pull permits for the rennovation, would we be required to demolish the front section to bring it into conformity on the setback line or does that typically get grandfathered in? None of our renovations would be changing exterior walls. The ony exterior change we are considering is potentially getting a permit to put a deck on the rear garage.

Thank you in advance for your help!