First published: Nov 2025

No Party for the Party Wall

TAKEAWAY Although the developer did not win, the law may soon shift in their favor. In June 2025, both houses of the New York State Legislature passed an amendment to Real Property Actions and Proceedings Law Section 881. If the Governor signs it, the new law would allow developers to ask a court for permission to install permanent encroachments, such as underpinning, when doing demolition or foundation work. This would be a major change — currently, courts can only grant temporary access. The new law is expected to face challenges, but it clearly tilts the balance toward developers. This case highlights why careful negotiation matters. The record in this case reveals some of the major concerns that may arise from an adjacent building’s construction including lack of adequate crack monitoring, rodent infestation, trespassing workers, attempted break-ins from the scaffolding, cancellation of the co-op’s property insurance on account of possible underpinning, and a major increase in insurance premiums going forward. It's important to be proactive. If a neighboring developer seeks access, boards should work closely with their attorney, architect, and engineer to negotiate the strongest possible license agreement. That agreement should ensure the developer reimburses the building for its legal and professional fees and includes protections for the property and residents. A well-drafted license agreement should address all of these risks — possibly including license fees, escrowed funds to cover ongoing costs, and clear procedures for handling any damage that occurs.

WHAT HAPPENED 351 West 20th St., a small brownstone co-op in Chelsea, shares a common party wall with its neighbor, 353 West 20th St.. The two properties are also separated by a second wall on the co-op’s side of the property, which stands on its own footing and is contiguous with, but structurally independent, from the party wall. 353 wants to do major renovations, including expanding its cellar. The project and excavation work will, unless protective measures are taken, cause structural damage to the co-op, so 353 proposed underpinning the party wall and the independent wall to strengthen the co-op’s foundation. The two parties have been negotiating a license agreement for the underpinning, but can’t come to terms, in part because the co-op is seeking provisions against the possibility it will lose its property insurance, or have to pay substantially higher premiums, should underpinning occur. Until the two sides can come to an agreement, the DOB has issued a stop-work order. 353 has sued the co-op to either allow it to underpin the party and independent walls or compel the co-op to perform the work for its own protection.

IN COURT The court ruled that the owners of 353 West 20th Street cannot underpin the co-op’s property without permission. Because part of the proposed work would extend onto the co-op’s side of the property line, the court found that doing so without consent would be trespassing. The judge rejected the claim that a shared party wall gives one owner the right to make permanent structural changes benefiting the other building, and also rejected the argument that the co-op was required by law to perform or allow the underpinning. The section of the Building Code cited by the 353 owners, the judge explained, does not force adjoining owners to carry out construction work or give access — it only defines who is responsible if damage occurs. In short, the co-op has no duty to allow or perform the underpinning. Instead, the court found that the presence of a license, or the adjoining property owner’s efforts to protect its property from excavation-related harm in the absence of a license, would be relevant in an action for money damages should the excavation damage the adjoining property. Summary judgment was denied and the court ruled in favor of the co-op. The remaining parts of the lawsuit, including the owners’ claims for damages, will proceed separately.

COUNSEL for the co-op MATTHEW BRETT Belkin Burden Goldman; for 353 owners ERIC THORSEN, LAURA MCKENZIE Quinn McCabe; Justice Gerald Lebovits