Building class

The building class is a two-character code in the city's assessment records classifying each property's principal structure and use: a letter for the broad family — walk-up apartments, elevator apartments, offices, warehouses, hotels, vacant land, and so on — followed by a second character refining the type within the family. The Department of Finance assigns and maintains the codes for assessment purposes.

Building class is among the most useful single fields in NYC property data: it distinguishes a rowhouse from a small apartment building at a glance, filters portfolios by asset type, and flags mismatches worth investigating — a lot whose building class disagrees with its certificate of occupancy or observed use is telling you to look closer. Because it is an assessment classification rather than a zoning determination, it describes what stands, not what may be built.