The Halsworth (645 West End Avenue)

Ajello's facade is a restrained, well-proportioned prewar composition, the developer's "H" reading as a quiet historical signature across the elevations. Though the building appears massive from the street, the modest 72-unit count produces larger average floor plates than its scale would suggest.

The apartments are arranged in the classic prewar manner — gracious entry galleries, separate dining rooms in the larger lines, and well-scaled principal rooms. The signature interior features are the 10-to-12-foot ceilings, the oak-paneled and beamed dining rooms, the stained glass, and the original moldings. Finish and configuration vary apartment to apartment after a century of individual ownership and renovation.

The Halsworth operates as a full-service pre-war cooperative with a resident superintendent. Residents enjoy a landscaped rooftop garden and a rooftop gym/exercise room — amenities richer than most prewar peers of this vintage — along with a bike room and private storage. Subtenants are permitted to use the gym and roof deck, and the bike room is available for a monthly fee billed to the shareholder.

The building's policies are well defined. A 5% flip tax on net profit is paid by the seller (with broker fee, reasonable legal fees, and city and state transfer taxes deductible from the calculation). Pets are permitted subject to board review, with an introduction letter describing the pet required. Subletting is allowed for an initial one-year term plus a single one-year renewal, with a sublet fee of 20% of monthly maintenance. Pied-à-terre purchases are considered case by case. Trusts are permitted with submission of the trust documents for co-op counsel review; LLC and corporate ownership are not allowed, and the building does not permit interest-only mortgages or guarantors. As a building within a designated historic district, exterior alterations are subject to landmark review.

Sales context at The Halsworth:

• Turnover is moderate for a building of 72 units — typically a handful of closings per year.
• Pricing spans a range tied to apartment size, floor, exposure, and renovation: light-filled prewar two- and three-bedrooms anchor the building, with larger configurations commanding premiums within the West End Avenue prewar market.
• Specific historical trades should be reviewed at the apartment level; this page does not assert individual sale prices.

The prewar interiors are the building's selling point. Ten-to-twelve-foot ceilings, oak-paneled dining rooms, and stained glass are rare survivors — a genuine quality-of-life differentiator versus thinner postwar stock.

The rooftop amenities are a real draw. A landscaped roof garden and rooftop gym are notable for a 1913 building, and they extend to subtenants as well as owners.

The financing and ownership rules are strict. Plan for a maximum mortgage with no interest-only structures, no LLC or corporate purchases, and a board that reviews trusts and pied-à-terre requests individually.

Budget the 5% flip tax into your resale math. It is paid by the seller on net profit, with standard deductions allowed.

The Ajello authorship and the period interiors are marketing assets. Listing copy should foreground the architect's reputation on West End Avenue, the soaring ceilings, the oak-paneled dining rooms, and the rooftop garden and gym.

Account for the 5% net-profit flip tax. It is a meaningful seller cost; price and net-proceeds conversations should reflect it from the outset.

Pricing requires apartment-level comparable analysis. With 72 units in mixed prewar configurations, floor, exposure, and renovation history drive value more than building averages.

Closing timelines are co-op standard. Plan for roughly 6–10 weeks from contract signing to closing.

If you're considering The Halsworth, also evaluate:

• 670 West End Avenue — nearby West End Avenue prewar co-op
• 680 West End Avenue — nearby West End Avenue prewar peer
• 685 West End Avenue — nearby West End Avenue building

The Roebling Team at Compass specializes in Central Park West, the Upper West Side, and the broader Park-facing Manhattan market. We publish this building profile because West End Avenue buyers and sellers deserve building-specific intelligence — architecture, board culture, transactional mechanics, and pricing at the apartment level — not generic market commentary.

If you're considering a purchase or sale at The Halsworth, a 30-minute consultation is the right starting point.