Due Diligence: Red Flags in a Building's History

Buying a building in New York City without doing a deep dive into its compliance history is like buying a used car without checking the Carfax—but with millions of dollars on the line. What looks like a pristine pre-war walk-up can actually be a ticking time bomb of unresolved violations, stalled permits, and impending local law fines.

Before closing on any commercial or multi-family property, engineers, architects, and expediters perform exhaustive due diligence. They dig through the Department of Buildings (DOB), Environmental Control Board (ECB), and Housing Preservation and Development (HPD) databases.

Here are the primary "red flags" professionals look for during that process, what they actually cost to fix, and how you can instantly uncover them using a Cornice PDF Compliance Report.

1. Open Class 1 (Immediately Hazardous) Violations

Open violations are common, but they are not all created equal. A minor HPD Class A violation for peeling paint in a hallway can be resolved by a handyman in an afternoon. A DOB Class 1 (Immediately Hazardous) violation, on the other hand, is a severe liability.

• The Risk: Class 1 violations carry base penalties starting around $2,500, but if the owner fails to certify correction (AEUHAZ), penalties compound quickly, sometimes reaching tens of thousands of dollars. They also halt any new permits from being issued for the building.
• What to look for: Unresolved ECB summonses with a "Class 1" or "Aggravated" status.

2. Stalled or "Signed Off" Missing Job Filings

A building's value is tied directly to its legal use. If the previous owner renovated the lobby or combined two apartments but never finalized the permits, the city considers that work illegal.

• The Risk: If work was completed but the job filing was never "Signed Off" (or never filed at all), you inherit the liability. When you apply for a new permit, the DOB inspector will spot the unpermitted work, issue a violation, and force you to legalize it (which often means ripping open walls) or revert it.
• What to look for: Jobs in the DOB system that have been in "Permit Issued" status for years without a "Sign-Off" or "Letter of Completion."

3. Active Neighbor Complaints (311)

The DOB relies heavily on public complaints to drive enforcement. A building with a high volume of active 311 complaints is a building with a target on its back.

• The Risk: Frequent complaints about illegal conversions (e.g., transient use/Airbnb), unpermitted construction, or falling debris often precede a surprise DOB audit. Once inspectors arrive, they can write violations for *anything* they see, not just the original complaint.
• What to look for: Multiple recent, active complaints in the BIS or DOB NOW systems regarding "Work Without a Permit" or "Illegal Conversion."

4. Local Law 97 Carbon Exposure

For buildings over 25,000 square feet, historical fines are only half the picture. The biggest financial liability may be sitting in the future.

• The Risk: Local Law 97 enforces strict carbon emissions caps starting in 2024, with limits dropping drastically in 2030. If the building has older, inefficient boiler systems or poor insulation, you could be inheriting six-figure annual tax penalties.
• What to look for: The building's LL84 energy benchmarking data, crossed against its upcoming 2030 emissions cap. If the penalty is high, you must factor the cost of a full HVAC retrofit into your purchase price.

5. Certificate of Occupancy Discrepancies

The Certificate of Occupancy (CofO) is the building's birth certificate. It dictates exactly how the building can be legally used.

• The Risk: If the ground floor is leased to a restaurant, but the CofO says "Manufacturing," the restaurant is operating illegally. A fire inspector or DOB agent can issue an immediate vacate order, destroying your rental income overnight. Furthermore, banks will rarely finance a building with a missing or conflicting CofO.
• What to look for: Ensure the existing CofO matches the actual, physical use of every floor of the building.