423 Atlantic Avenue (The Ex-Lax Building)

The property is an assemblage rather than a building: roughly 331 feet of Atlantic Avenue frontage on a 29,745-square-foot lot, carrying about 101,902 square feet across six stories. The 1925 Ex-Lax headquarters at 423 is the Art Deco element; 435 through 443 are the older Romanesque Revival structures of about 1880. The complex was never designed as a single composition, and it does not read as one — the interest is in the seam.

Inside, the stock is loft: apartments carved from factory and warehouse floor plates during the 1979–81 rehabilitation. The plan's own arithmetic — 58 units across 145 zoning rooms — describes generously open apartments rather than a conventional room-count product, and the useful measures for a buyer are floor area, ceiling height, window wall and column condition. Those measures vary meaningfully between the 1925 building and the nineteenth-century structures, which have different floor-to-floor heights, different structural systems and different window openings. A comparable pulled from the wrong part of the complex is not a comparable.

The ground floor and basement carry a commercial component of roughly 6,978 square feet. That space was contentious at conversion — the cooperative's claims included the cost of making it rentable and the sponsor's overstatement of its rental value — and it remains an income line worth reading in the current statements rather than taking on faith.

Because the building sits outside the historic district, window replacement, storefront work and façade treatment are governed by the Department of Buildings and the board rather than by Landmarks. In a six-story masonry complex of this age, that removes a layer of cost and delay from any exterior project — and it also means the board's own alteration agreement is the only architectural control over what shareholders do.

423-443 Tenants Corp. has operated the complex since the 1980-era closing, and the operating profile is that of a mid-size loft cooperative with a diversified income base: maintenance from 3,086 shares, commercial rent from the ground floor and basement, and whatever sublet and storage income the board books. The sponsor's position was fully wound down early — by the January 1982 amendment it retained a single apartment, 5C — so this has been a shareholder-controlled building for more than four decades.

The capital agenda in a building of this construction and vintage is legible without guesswork: façade and parapet condition, roof, boiler and heating distribution, elevator, and the window openings across two distinct structures. The recorded six-story height does not establish FISP applicability, which begins above six stories; verify the height and requirements for each structure. Those were precisely the systems at issue in the conversion-era litigation, which means the questions to ask are specific rather than general. Ask what has been replaced and when, ask for the last three years of audited statements and the current assessment schedule, and ask for the board minutes. Management history and current agent details are maintained in The Roebling Research Library and confirmed with clients during diligence.

Two operating items deserve their own line. The commercial tenancy is a real revenue and real risk item on a corridor whose retail composition has shifted substantially; read the lease terms and expiry. And the Atlantic Avenue frontage itself is an operating condition — a wide, heavily trafficked arterial that is also one of Brooklyn's better retail streets. Exposure to it is the single largest driver of livability differences inside the building.

Purchaser review: Full cooperative board approval. Expect the standard package and an interview; confirm the current requirements, timeline and application fee with the managing agent, and build the review period into contract timelines.

Subletting: The proprietary lease permits a shareholder to sell shares and assign the lease, or to sublet the apartment, upon obtaining the required consents. The current board's sublet policy, term limits and fee schedule should be confirmed in writing — sublet rules are board-made and change.

Alterations: Governed by the cooperative's alteration agreement, which is maintained as a building document. Because the building is outside the historic district, exterior and window work does not require Landmarks approval, but it does require board consent and Department of Buildings compliance.

Financing / minimum down: Not publicly documented. Confirm the board's current maximum financing percentage at offer stage — in a loft cooperative this is frequently the deciding term of a deal.

Flip tax, pets, pied-à-terre: Not documented in the materials reviewed. Confirm each against the current house rules and board policy.

Recent sales

Recent transfers 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. $/sf is measured on the latest sales with reliable square footage (2025): a median $1,483/sf (floor-adjusted) across 1 sale. The building has traded as recently as 2026. Median listing discount 0.0% from the last ask.

Sales sourced from NYC Department of Finance recorded transfers (BBL 3-00178-0054). 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 on co-ops is not officially recorded, figures shown are approximate.

Read the capital record against the conversion history. The systems disputed in the early-1980s litigation — boiler and steam distribution, sprinkler, roof, parapets, water tank, column fireproofing, window caulking and lintels — are the same systems that drive capital cost today. Ask what has been replaced, when, and how it was funded.

The building is outside the historic district, and that cuts both ways. No Landmarks review for your windows or your storefront, and no Landmarks protection for the blockfront around you. The 2018 extension stopped at 389 Atlantic Avenue.

Know which building you are in. The 1925 Art Deco headquarters and the c. 1880 structures next door have different ceiling heights, different structural systems and different windows. Comparables must match.

Underwrite the commercial income. Roughly 6,978 square feet of ground-floor and basement commercial space supports the maintenance base. Read the lease, the term and the tenant.

Budget the board process. This is a full-approval cooperative with an interview. Confirm the current financing limit before you write an offer — in a loft co-op it is frequently the deal term that matters most.

Sell the history, precisely. One of Brooklyn's first factory-to-loft cooperative conversions, in the 1925 headquarters of a company that was a household name by 1926. That is a specific, verifiable story, and it is better than a generic loft pitch.

Lead with volume. Ceiling height, window wall and open plate are what buyers are paying for. Photograph them; do not photograph rooms.

Document renovation. Spread inside this building is driven by finish state more than by floor. If the apartment has been reworked, put the permits, the scope and the dates in the package.

Present the capital story. A forty-five-year-old conversion in a hundred-year-old complex needs a completed-projects narrative. Silence invites the buyer to assume the worst.

Anchor within your structure. Do not price a c. 1880 apartment off a 1925 comparable, or a front unit off a rear one.

If you're considering 423 Atlantic Avenue, also evaluate:

• 505 Court Street (Court Street Lofts) — the Carroll Gardens loft conversion; compare ownership and purchase requirements separately from loft format
• 96 Schermerhorn Street (Boerum Court) — elevator cooperative of comparable scale a few blocks northwest
• 166 State Street — cooperative on the north side of the Atlantic Avenue line
• 200 Congress Street — the largest cooperative in Cobble Hill; the accessible-tier co-op alternative west of Court Street
• 556 State Street (Boerum Heights) — the condominium alternative on the same avenue further east
• 509 Pacific Street (The Hendrik) — boutique Boerum Hill condominium; the new-construction contrast
• 71 Smith Street (The Boerum) — condominium at the Smith Street spine
• 10 Nevins Street (The Brooklyn Grove) — larger Boerum Hill condominium toward Downtown
• 214 Clinton Street — small Cobble Hill cooperative inside the historic district; the landmark contrast