21 West 39 Street, Manhattan 10018 is a 2,468 square foot lot zoned M1-9A/R12. RunEnvelope’s engine finds an as-of-right scheme with homes of 44,414 sf (AIRS Senior Housing (100% Affordable)), against 13,689 sf built on the lot today.
That leaves 30,725 sf more floor area than stands here now, if the existing building were replaced. The largest scheme with homes and no affordability obligation holds 37,020 sf (Max Apartments).
City Planning’s PLUTO file lists a residential FAR of 15.00 for this lot, which at 2,468 sf of land is 37,020 sf. The engine’s largest residential-only scheme without an affordability obligation (Max Apartments) holds 37,020 sf, close to that simple multiplication.
Quality Housing height limit in R12 on a narrow street: 325 ft (395 ft with the affordability preference). From the district’s rule set.
The largest 6 as-of-right schemes RunEnvelope’s engine produced for this lot, by zoning floor area. A full study also models the building itself: floor plates, heights, setbacks, unit mix and parking.
| Scheme | Type | Floor area | FAR | Homes |
|---|---|---|---|---|
| AIRS Senior Housing (100% Affordable) | Income-restricted housing | 44,414 | 18.00 | 30 |
| Existing Building: Retain & Enlarge (ZR 54-31) | Keeps existing building | 37,028 | 15.00 | None |
| Max Apartments | Housing | 37,020 | 15.00 | 77 |
| Residential + Community Facility | Mixed use with homes | 37,020 | 15.00 | 27 |
| Community Facility | Community facility | 37,020 | 15.00 | None |
| Mixed-Use | Mixed use with homes | 37,019 | 15.00 | 31 |
Floor area is zoning floor area in square feet. Highlighted: the largest scheme with homes. Income-restricted schemes (Universal Affordability Preference, AIRS senior housing) require a share or all of the homes to be affordable. Shared housing counts rooms, not apartments. Schemes that need a landmark transfer of development rights, the FRESH food store bonus or a stack of every program are left off this page; the full study shows them.
As-of-right only: what the Zoning Resolution allows without a variance, special permit or rezoning. Computed by RunEnvelope’s zoning engine on October 21, 2026 from PLUTO 26v2 lot data, in screening mode: the engine uses the City’s recorded lot area and dimensions, not a surveyed lot outline.
This is not a professional opinion, an appraisal or a statement that anything will or should be built here. Existing tenants, leases and the owner’s plans are not part of it.
Why this lot has a page: we publish pages only for lots that clear a set of data quality and headroom tests.
The closest published lots in Manhattan, same zoning district first. All Manhattan lots.