15 West 20th Street (Altair 20)
15 West 20th Street, New York, NY 10011
- Year built
- 1906
- Type
- Condominium
- Units
- 17
- Floors
- 11
- Landmark
- Designated
- Amenities
- Landscaped roof deck with cabanas and grills, fitness center, private storage, ground-floor retail
- Pets
- Permitted per architectural and listing records
Every recorded sale at this building, 2021–2026
Price-per-square-foot over time, the line- and floor-premium curves, and every recorded sale.
- Recorded sales
- 15
- On record
- 2021–2026
Altair 20 is what a Flatiron loft conversion looks like when it is done at boutique scale: 17 residences in an 11-story 1906 store-and-loft building, two or fewer units on most floors, wood-burning fireplaces in the apartments, and condominium transfer mechanics in a district where much of the pre-war loft stock converted as co-ops a generation earlier. For buyers who want Ladies' Mile architecture — the limestone base, the bandcoursed brick, the deep floor plates — without a co-op board interview, the building occupies a genuinely thin slice of the market.
The conversion is also an early chapter in a familiar New York story. The sponsor, Strategic Chelsea LLC, executed the project in 2005–07, and the building sits in Extell Development's published portfolio alongside its sister conversion, Altair 18 at 32 West 18th Street — work that predates the firm's supertall era. The offering plan on file in The Roebling Research Library documents the arc precisely: a plan dated August 8, 2005, a total residential offering of $44,850,000 across 17 units, sponsor pricing of roughly $2.2–2.8 million for the A- and B-line residences by the Second Amendment in April 2006, and at least seven amendments through mid-2007 as the budget, tax opinion, and first operating year were trued up. That paper trail — including the plan's disclosed special risk that the sponsor retained the right to rent rather than sell units — is exactly the kind of documentation buyers' counsel should read, and we have it.
The original building deserves its own credit. Architectural records attribute the 1906 design to Lafayette A. Goldstone, working in the Neo-Renaissance commercial vocabulary of the Ladies' Mile shopping corridor; the historic district designation (1989) now protects the facade. The conversion kept the loft virtues — scale, ceiling height, big window walls — and layered in finishes that were ambitious for the period.
Architecture and unit composition
The building rises 11 stories on a 56-foot-wide mid-block lot, with ground-floor retail and sidewalk landscaping at the base. The residential mix is dominated by full- and half-floor two- and three-bedroom lofts: the B-line units run to 27-to-28-foot living/dining rooms with pass-through kitchens, and several lines carry dedicated home offices. The trophy is the duplex penthouse — 3,223 square feet with three bedrooms and nearly 2,000 square feet of terraces, a limestone-clad foyer, vaulted-ceiling primary suite, and a private loggia, per architectural records. Wood-burning fireplaces run through the residences, a scarce feature in Flatiron condominium stock of any vintage.
Building operations
This is a boutique condominium, and it operates like one: a part-time doorman, a live-in superintendent, and a 17-unit owners' association rather than a full-service staff stack. The amenity set is compact but real — a fitness center, private storage, and a landscaped common roof deck with cabanas and grills. Buyers comparing against full-service Flatiron buildings should weigh the materially lower staffing overhead against package logistics and off-hours coverage. Exterior work, including anything visible at the roofline, runs through Landmarks review given the historic district. The offering plan and amendments are on file in The Roebling Research Library and available to clients during diligence.
Local Law 97
- 2024–2029 annual penalty
- $0 (under cap)
- 2030–2034 annual penalty
- $28,115/yr
- Per unit / month range
- $0 – $138
Recent sales
The retrade record
Lines that have traded more than once in the public record — the building’s appreciation arc, apartment by apartment.
Recent closings at this building, sourced from NYC Department of Finance records. Apartment-level detail (line, condition, asking-price context) verified upon consultation request.
| Date | Unit | Price |
|---|---|---|
| Apr 28, 2026 | 2 | $3,125,000 |
| Feb 10, 2026 | 10A | $3,300,000 |
| Jan 2, 2026 | OFF8 | $18,270,000 |
| Dec 3, 2025 | 9A | $3,200,000 |
| Dec 1, 2025 | — | $9,294,074.94 |
| Oct 3, 2025 | 10PH1 | $9,950,000 |
Full closing history with price-per-square-foot over time, the complete retrade record, and every line that has traded.
Sales sourced from NYC Department of Finance recorded transfers (BBL 1-00822-7504) and verified listing data. Apartment-level facts (line, condition, asking-price context) curated and cross-verified by The Roebling Team research desk. Not all transactions cross-verify with ACRIS records — sponsor and LLC purchases sometimes record at stipulated values rather than market price.
What to know if you’re buying
The structure is the headline. Condominium mechanics in a pre-war loft envelope — no board interview, condo-standard transfer terms, and flexibility on entity and financing structures that the surrounding loft co-ops do not offer. Confirm specifics against the by-laws with your attorney.
Seventeen units means seventeen checkbooks. In a building this small, capital projects divide across few owners, and a single major facade or roof cycle moves common charges meaningfully. Review the budget, reserve position, and recent meeting minutes carefully; the offering plan on file gives you the baseline operating framework to compare against.
Underwrite the staffing model honestly. A part-time doorman and live-in super suit most loft buyers; they do not suit buyers expecting white-glove service. Price your own service expectations before contract.
Landmarks applies to the envelope. The Ladies' Mile Historic District protects the facade — a guarantee of the block's character and a process constraint on window, mechanical, and rooftop work. Review the building's alteration history during diligence.
Run the math at the asking tier. Nearly every unit in the building trades above the mansion-tax thresholds. Run the Mansion Tax Calculator and the Buyer Closing Cost Calculator before offering.
What to know if you’re selling
Sell the scarcity stack. Boutique condo, pre-war loft envelope, wood-burning fireplace, historic-district block, two-or-fewer-units-per-floor privacy — name the structural facts. The Flatiron buyer cross-shopping new glass product responds to exactly this list.
Same-line history is thin, so position against the corridor. With 17 units, your comparable set is the Flatiron boutique conversion market, not just the building. We anchor pricing to corridor comps and the unit's specific light, condition, and fireplace count.
Document the fireplace and finish provenance. Conversion-era finishes are now twenty years old; renovated units should market the upgrade history, and original-condition units should be priced to the renovation math. Run the Renovation Cost Calculator against your asking strategy.
Comparable buildings
If you're considering 15 West 20th Street, also evaluate:
- Altair 18 (32 West 18th Street) — the sister conversion by the same sponsor team; the most direct peer
- 45 East 22nd Street — the Flatiron's new-construction tower alternative at a higher price point
- 15 Union Square West — boutique condo conversion at the square; the glass-and-history alternative
- 141 Fifth Avenue — domed corner condominium conversion of the same Ladies' Mile vintage
- The Grand Madison (225 Fifth Avenue) — larger pre-war conversion on Madison Square Park
- One Madison (23 East 22nd Street) — the park-facing modern boutique tower
- 260 Park Avenue South — landmarked pre-war condo conversion at the Gramercy seam
The Roebling Team at 15 West 20th Street (Altair 20)
The Roebling Team at Compass works the Flatiron and Chelsea corridors as a core practice area. We publish this building profile because Altair 20 buyers and sellers deserve building-specific intelligence — conversion documentation, policy framework, and boutique-condo comparables — not generic neighborhood commentary.
If you're considering a transaction at 15 West 20th Street, a 30-minute consultation is the right starting point.