Before you buy a Chicago 3-flat.

A 3-flat is three homes stacked on one foundation under one roof. The units drive rent. The shared parts (shell, porches, basement, mechanicals) drive the surprises. Walk the building with this list before your offer, and bring a flashlight.

1. The shared shell

• Roof: age, soft spots, flashing at parapets and chimneys, and stains on the top-floor ceilings.
• Masonry: cracked or missing mortar, bowed walls, cracked lintels above windows, and the parapet.
• Foundation and basement walls: cracks, water staining, efflorescence, and a musty smell.
• Windows: age, rot, and whether each unit's windows open and lock.
• Gutters, downspouts, and grading: water should move away from the building.
• Common stairs and halls: handrails, lighting, doors, and smoke detection.

2. Porches

• Rear porch structure: posts, footings, beams, joists, and connections to the building.
• Guards and handrails on every level, and stairs that don't flex.
• Rot, especially at post bases and where decking meets the building.
• Any sign of recent porch work, and whether it was permitted.

Why it matters: Chicago holds existing porches to its minimum standards no matter when they were built. Structural porch repairs always need a permit, and on a multi-story porch anything beyond a 25% repair needs architect or structural engineer drawings.

3. Unit by unit (×3)

• Heat: each unit's system, its age, and who pays for it.
• Water heater: age, venting, and whether each unit has its own.
• Electrical: panel per unit, service size, visible old wiring, and missing outlet covers.
• Plumbing: water pressure on the top floor, leaks under sinks, and drain speed.
• Kitchen and bath: condition, layout, and ventilation.
• Smoke alarms: in buildings built before 2018, within 15 feet of each sleeping room, one on every level including the basement, and one at the top of each shared stairway. Removable-battery alarms must be replaced by January 1, 2033.
• Carbon monoxide alarms within 15 feet of sleeping rooms and in the same room as each furnace, boiler, or water heater.
• Bedroom egress: windows that open and are big enough to get out of.

4. The basement

• Is there a basement or garden unit? Ask whether it's a legal unit, and get proof. If you plan to add one, check whether the building qualifies under Chicago's additional dwelling unit ordinance.
• Ceiling height, window sizes, and a second way out, if a unit is planned or already there.
• Shared mechanicals: boilers, meters, water service, and main drain.
• Water: sump pump, drain tile, backflow, and signs of past flooding.

5. Paperwork and permits

• Open building permits or violations on the property.
• Work that looks newer than the last permit, a sign of unpermitted renovation.
• Existing code problems: in Chicago, any permitted rehab must fix all readily apparent violations of the existing-building code, cited or not.
• If the building is vacant: Chicago requires registration within 30 days, renewed every six months ($300 per six-month period), plus securing and maintaining the building.
• Built before 1978: federal lead-based paint disclosure applies to the sale, and renovation that disturbs paint must be done by an EPA- or state-certified firm.
• Taxes after the rehab: the Cook County Assessor reviews building permits and may reassess a property after significant work.
• Current leases, rents, deposits, and which units are occupied at closing.

6. The numbers

• Current and after-rehab rent for each unit.
• Which utilities the owner pays.
• Your exit: flip, BRRRR, or hold.
• Rehab estimate built from this list, not a per-square-foot guess. How to estimate rehab costs before you buy.
• Holding costs for the length of the rehab.

Found something that worries you?

That's the point of the list. Send Mason the address and your notes, and we'll talk through what it means for the rehab before you make your offer. Under contract? Book a scope visit and choose Pre-Acquisition Walkthrough for an itemized number.