Chicago Rear Addition (RS3 Zoning)

[Darius Hoffman]

Hello - I am seeking some input on building a fairly simple rear addition on a prospective SFH and long-term hold. I want to ensure I'm not overlooking anything prior to making an offer. Most likely it would be an expanded living room + 1 bedroom & no plumbing involved.

The existing house is RS-3 Zoned on a standard 25' x 125' lot and the home's current length is about 50' offering about ~800 sq/ft on the main level.  That does not include the attic or basement. My understanding is that the Rear Setback = 50ft or 28% (35 ft) // Rear Yard Min = 225 sq (25' x 9 ').

Is there anything else I should know about this kind of project? I do plan to do the work permitted with the city and utilize an architect.  Assuming the size is 20' x 25' is 50-80K a reasonable ball park estimate?

I'd also be open to any local referrals or recommendations via DM

Thank You