NYC Due Diligence: Websites to Check Before You Buy

Most buyers stop at ACRIS. That’s understandable; ACRIS is the pillar page in this conversation, and it’s where deeds, mortgages, and liens are stored. But ACRIS tells you who owns the building and what they owe on it. It doesn’t tell you if the radiator has been broken since March. It also doesn’t say if the “junior 4” was legally meant to be a one-bedroom.

That’s a different set of records, run by different agencies, none of which talk to each other. Welcome to New York.

What should I actually check before making an offer?

Beyond ACRIS, run the building and the unit through these five places. Each one takes a few minutes and has, at some point, saved a buyer from a bad closing.

• DOB BIS (Building Information System): open and past Department of Buildings violations, permits, and complaints, going back to the 1980s. Free, no login.
• HPD Online: Housing Preservation and Development violations (Class A, B, C by severity), plus any housing court cases against the landlord or building.
• DOB NOW: where you pull the current Certificate of Occupancy to check whether the unit’s actual layout matches what the city has on file.
• ZoLa, the Department of City Planning’s zoning map, confirms the zoning district, commercial overlays, and whether anything unusual is going on with the lot.
• FloodHelpNY or the FEMA Flood Map Service Center tells you if the building sits in a Special Flood Hazard Area, which can mean mandatory flood insurance on top of your regular policy.
• Discover NYC Landmarks, the Landmarks Preservation Commission’s map of all 141 historic districts: if the building’s in one, your future renovation plans need LPC approval, not just a contractor.
• StreetEasy’s Past Sales tab on the building page shows what other units actually closed for, not just what they were listed for. StreetEasy explains how to find it here and links directly to the ACRIS-recorded closing for each sale.

How do I check a building’s DOB violations?

Go to DOB BIS and pull up “Property Profile Overview” for the address. Open, active violations are the ones that matter most, since they can hold up your closing until they’re resolved.

Every violation gets adjudicated at OATH, the city’s Office of Administrative Trials and Hearings, where you can see whether it’s pending, upheld, dismissed, or in default. A pile of defaulted violations is a landlord who ignores the city, which tells you something about how they’ll treat your maintenance requests too.

Real estate attorney Peter Zinkovetsky’s due diligence checklist puts violation searches across DOB, FDNY, and OATH/ECB records near the top, right alongside verifying the Certificate of Occupancy actually matches how the building is being used.

What does HPD Online actually show me?

HPD Online is where you check the landlord’s track record, not just the building’s. Search the address, and you’ll see registration data, violations, and any housing court litigation against the owner.

Class C violations are the ones to worry about; they’re classified as immediately hazardous with a 24-hour cure window. A building with a stack of unresolved Class C violations, or a landlord who’s shown up in housing court repeatedly, is a pattern, not a coincidence.

As Brick Underground’s guide to HPD Online puts it, the complaints tab lets you see if other residents have already flagged the exact problem you’re worried about.

How do I know if the unit was illegally converted?

Pull the Certificate of Occupancy through DOB NOW for newer filings, or the legacy BIS system for older buildings. Then compare it to what you’re actually being shown.

If the listing says three bedrooms and the C of O says two, someone put up a wall without a permit. That’s not a quirky layout; it’s an illegal conversion, and the NYC Department of Buildings runs entire campaigns warning buyers about exactly this. Lenders won’t finance a purchase if the certificate doesn’t match the building’s actual use, so this can kill your closing outright, not just your resale value.

Does it matter if the building is in a flood zone?

Yes, and it’s an easy thing to miss if you’re apartment hunting in a neighborhood that doesn’t scream “waterfront.” Check FloodHelpNY or the FEMA Map Service Center by address.

If the building is located in a Special Flood Hazard Area (zones starting with A or V) and you’re taking out a federally backed mortgage, your lender will require flood insurance, which isn’t covered by a standard homeowner’s policy. A National Flood Insurance Program policy often costs less than $400 per year. You should know this cost before you sign a contract, not during it. And if the building ever received federal disaster assistance, the insurance requirement stays attached to the property forever, for you and whoever buys it after you.

What if I want to renovate? Is the building landmarked?

Check the Discover NYC Landmarks map from the Landmarks Preservation Commission before you fall in love with the exposed brick and the plans to open up the kitchen.

New York has 141 historic districts covering nearly 34,000 buildings. If yours is one of them, exterior changes and sometimes interior ones need LPC approval on top of a normal DOB permit. That’s a longer timeline and a real budget line, not a footnote.

How do I know if the asking price is realistic?

Open the building’s page on StreetEasy and click into the Past Sales tab. It shows what units in that specific building actually closed for, alongside what they were originally asking, so you can see the real gap between ask and sale price for that address.

Brick Underground calls StreetEasy’s pricing history one of the most useful things buyers can check before submitting an offer, and closed sales that are linked through to ACRIS give you the recorded price, not the number someone typed into a listing.

Everything here is what ACRIS won’t tell you. For what it does cover, deeds, mortgages, and liens, see our full ACRIS guide.

Buying a co-op instead of a condo? The violation and zoning checks above still apply, but you’ll also want a co-op lien search, since ACRIS won’t show anything for a share sale. And if you want the full reference list of every government database mentioned here, not just the walkthrough, see our complete due diligence links list.

Frequently asked questions

Do I need a lawyer to do any of this myself?
No, all of these sites are free and public; no login required. But a real estate attorney should still review title, the offering plan or co-op board package, and anything the searches turn up, before you sign a contract.

How long does this kind of self-directed check actually take?
Fifteen to twenty minutes per building if nothing’s wrong. If DOB BIS or HPD Online turns up a long violation history, budget more time to actually read what each one says.

What’s the difference between a DOB violation and an HPD violation?
DOB violations are about the physical building, construction, permits, and structural issues. HPD violations are about housing conditions and landlord obligations under the Housing Maintenance Code, including heat, pests, and repairs. A building can have a clean DOB record and a rough HPD record, or vice versa.

Can open violations actually stop a closing?
Yes. Open, active violations can delay or block a closing until they’re resolved or the seller agrees to escrow funds to cover them. This is exactly why attorneys like Peter Zinkovetsky put violation searches early in a due diligence checklist, not as a last-minute check.

Is the Certificate of Occupancy the same thing as ACRIS records?
No. ACRIS holds deeds, mortgages, liens, ownership, and money. The Certificate of Occupancy, obtained from DOB NOW or BIS, describes the building’s legal use and layout. You need both; they answer different questions.

What if the building doesn’t show up in ZoLa at all?
That’s unusual and worth flagging directly to your attorney. Every lot in the five boroughs has a zoning designation, so a blank result usually means an address or block/lot mismatch worth double-checking rather than an actual gap in the record.

Written by Nicole Fishman Benoliel

Co-founder of NestApple and a lawyer admitted to the New York bar, not currently practising.