NYC Building Class Codes Explained: A0–Z9 Cheatsheet

On every NYC property record, you'll see a "building class" — a one-letter, one-digit code like "C1," "D4," "O6," or "S9." It's the city's primary taxonomy for what kind of building this is. Tax class, financing eligibility, allowed renovations, and even insurance pricing all flow from this code.

This guide is a cheatsheet for the codes you'll actually encounter, what each one means, and what the number-suffix nuance signals.

How the code structure works

Every code is one letter + one digit. The letter is the category; the digit is the subcategory.

• Letter — general use type (residential, commercial, industrial, etc.)
• Digit — nuance within that category (size, era, configuration)

Residential codes (the ones you'll see most)

A — 1-family residential

• A0 — Cape Cod
• A1 — Two-story detached (small or moderate)
• A2 — One-story permanent living quarters
• A3 — Large-suburban-style
• A4 — City Residential
• A5 — Attached or semi-detached
• A6 — Summer cottage
• A7 — Mansion
• A8 — Bungalow colony / land coop owned
• A9 — Miscellaneous one-family

Tax Class 1 (lowest residential tax rate, 6% cap). Mortgage-friendly for owner-occupants.

B — 2-family residential

• B1 — Two-family brick
• B2 — Two-family frame
• B3 — Two-family converted from one-family
• B9 — Miscellaneous two-family

Tax Class 1.

C — Walk-up apartment (3+ units)

• C0 — Three-family
• C1 — Over six families without stores
• C2 — Five to six families
• C3 — Four-families
• C4 — Old-law tenement (built pre-1929)
• C5 — Converted dwellings or rooming houses
• C6 — Walk-up co-op
• C7 — Walk-up apartment over commercial
• C8 — Walk-up co-op apartment over commercial
• C9 — Garden apartments

Tax Class 2 (residential 4+ units, income-approach valuation). What most NYC renters live in.

D — Elevator apartment

• D0 — Elevator co-op (converted)
• D1 — Elevator apartment, semi-fireproof, low-rise
• D2 — Elevator apartment, semi-fireproof, mid-rise
• D3 — Elevator apartment, semi-fireproof, high-rise
• D4 — Elevator co-op
• D5 — Elevator condo
• D6 — Elevator apartment with commercial
• D7 — Elevator co-op with commercial
• D8 — Elevator condo with commercial
• D9 — Miscellaneous elevator apartment

R — Condo unit

• R0 — Condo, governmental
• R1 — Condo, one-family
• R2 — Condo, walk-up apartment
• R3 — Condo, one-family (detached)
• R4 — Condo, residential unit in two-to-ten-unit elevator
• R5 — Condo, commercial unit
• R6 — Condo, residential unit in 2-10 unit walk-up
• R7 — Condo, residential unit in five-or-more-unit elevator
• R8 — Condo, retail unit in larger building
• R9 — Condo, co-op converted to condo

Tax Class 2 (condos use a different valuation method — assessed at the lower of comparable-rental or income approach).

Common commercial codes

O — Office building

• O1-O3 — Office buildings, sized small to large
• O4 — Office with stores
• O5 — Office, professional
• O6 — Office with apartments above
• O7 — Office with bank
• O8 — Office with public garage
• O9 — Miscellaneous office

K — Store / retail

• K1 — One-story retail
• K2 — Multi-story department store
• K3 — Shopping center
• K4 — Department store
• K5 — Diner / luncheonette
• K6 — Shopping center over 100,000 sf
• K7 — Banking
• K9 — Miscellaneous store

Other useful categories

• F — Factory / industrial
• G — Garage / parking
• H — Hotel
• I — Hospital / health
• J — Theater / cultural
• L — Loft
• M — Religious
• N — Asylum / home
• P — Public assembly
• Q — Outdoor recreation
• S — Mixed use (residential + commercial together)
• T — Transportation
• U — Utility
• V — Vacant land
• W — Educational
• Y — Selected governmental
• Z — Miscellaneous

Building class → tax class

NYC has 4 tax classes; building class largely determines which one your property falls into:

• Tax Class 1 — A and B codes (1-3 family). Capped at 6% assessment ratio.
• Tax Class 2 — C, D, R codes (4+ family residential, condos, co-ops). Income approach valuation.
• Tax Class 3 — Utility property (rare for individual owners).
• Tax Class 4 — Commercial + industrial (most O, K, F codes). Highest tax rate.

Mixed-use gotchas (S codes)

S codes are tricky. An "S2" building is 4+ residential units + retail on the ground floor. It's taxed mostly as residential but the commercial portion has different rules. If you're considering buying or renting in an S-code building, ask whether your unit is on the residential or commercial portion of the C of O.

How to find a building's class

Three places:

1. NYC PLUTO data ("bldgclass" field)
2. DOF property tax bill (header)
3. Our audit — we surface the class with a plain-English label

Run a free audit on any NYC address →

Related reading

For how building class interacts with the Certificate of Occupancy (which says what use is approved), see Certificate of Occupancy explained.