21 South William Street

Built in 1927 as Block Hall, a private club, and designed by architect William Neil Smith, 21 South William Street is a seven-story neo-Tudor / Tudor Revival building — a rare architectural idiom in the Financial District. The building fronts both South William and Stone Streets, taking advantage of the bend in South William that defines the Stone Street enclave. It was converted from the club to a residential condominium in 2005, following the 2004 acquisition of the building by Kennelly Development Co. for roughly $4.5 million.

The residential inventory totals 31 apartments. The units carry high ceilings and premium appliances, the interior signatures of a well-executed landmark conversion. The building's amenity infrastructure is unusually complete for its scale: a lower-level fitness room, laundry on every floor, a secure package room, and a furnished rooftop terrace with East River views — the building's premier shared amenity and a genuine outdoor asset in the dense Stone Street enclave.

21 South William Street operates as a condominium. Staffing runs a part-time attended lobby supplemented by a virtual/remote doorman with a video intercom, an efficient hybrid model that provides coverage without the cost of a full-time staffed lobby. The amenity package includes an elevator, laundry on every floor, a lower-level fitness room, a secure package room, and the furnished rooftop terrace with East River views.

The ownership and policy picture is clean and flexible. Dogs and cats are allowed. Subletting and rentals are allowed, making the building investor and pied-a-terre friendly — an uncommon combination of amenity depth and rental flexibility. There is no ground lease and no HDFC restriction; the units are individually deeded. The building's Stone Street Historic District status imposes review on exterior alterations — a standard feature of historic-district ownership, not a sign of distress. Common-charge and assessment specifics should be confirmed at the unit level.

Recent sales

Recent closings at this building, from The Roebling Research Library. Prices are the transfer amounts recorded with the NYC Department of Finance; apartment-level detail is checked against the building’s own file in The Roebling Research Library before publishing.

Market read. Most recent trades (2023) cleared a median $1,134/sf (floor-adjusted) across 3 sales. Floor-adjusted means each sale is restated to a constant mix of floors, so the figure can differ from the plain median of the sales listed above. Median listing discount 2.4% from the last ask — a recurring negotiation gap worth pricing into any offer or listing strategy.

Sales sourced from NYC Department of Finance recorded transfers (BBL 1-00029-7503). Apartment-level facts (line, condition, asking-price context) curated and cross-verified in The Roebling Research Library. Not all transactions cross-verify with ACRIS records — sponsor and LLC purchases sometimes record at stipulated values rather than market price; square footage from recorded condo declarations and offering plans.

Block Hall was built in 1927 as a private social, athletic, and luncheon club for banking and marine-insurance businessmen, and named for Adriaen Block, the Dutch explorer. As a club it was planned with squash, racquets, and handball courts and an upper-floor gym, and it later housed the Italian Alps Restaurant. That club heritage is the reason for the building's distinctive neo-Tudor character and its amenity infrastructure, and it remains part of the building's identity as a residential condominium in the Stone Street Historic District.

The landmark conversion is the architectural argument. A 1927 neo-Tudor club converted to residences is a rare offering in the tower-dominated Financial District. The Tudor Revival exterior, the high ceilings, and the Stone Street enclave setting are the credentials.

The amenity package is complete for the scale. A lower-level fitness room, laundry on every floor, a secure package room, and a furnished rooftop terrace with East River views are substantial amenities for a 31-unit building. The hybrid lobby staffing — part-time attended plus a virtual/remote doorman with video intercom — provides coverage efficiently.

The rental flexibility is genuine. Subletting and rentals are allowed, and dogs and cats are permitted. For investors and pied-a-terre buyers, this is a functional and flexible asset, which is uncommon alongside amenity depth of this kind.

The ownership is clean. No ground lease, not HDFC — individually deeded units with straightforward title. The one structural consideration is the Stone Street Historic District status, which imposes review on exterior alterations. That is a normal feature of historic-district ownership, not distress; understand it before planning any facade-affecting work.

Verify the current pricing. Given the boutique scale and the presence of at least one non-arm's-length transfer in the record, confirm recent arm's-length closing prices against the latest recorded transfers rather than relying on aggregated figures.

Lead with the architecture and the amenity depth. The 1927 neo-Tudor club conversion, the Stone Street Historic District setting, and the furnished rooftop terrace with East River views are the anchors. The club heritage — Block Hall, named for Adriaen Block — is a genuine story that sets the building apart.

Position the rental flexibility. Subletting and rentals are allowed, which broadens the buyer pool to include investors and pied-a-terre purchasers alongside owner-occupants. That flexibility is uncommon in an amenitized landmark building.

Price against the latest recorded transfers. The relevant comparable is the most recent arm's-length closing on a similar layout, not an in-building median, and the January 2024 "$0" deed correction should be disregarded as a comp.

Frame the landmark status accurately. Exterior-alteration review is a standard feature of the Stone Street Historic District, not a limitation on ownership. Position it as part of the building's protected character.

If you're considering 21 South William Street, also evaluate nearby Financial District and Stone Street condominiums — comparable boutique and landmark-district conversion buildings in the Stone Street enclave and the surrounding Financial District that combine individually deeded ownership with the neighborhood's amenity and rental flexibility.