Combining condominium apartments is an effective strategy for creating larger homes within New York City’s dense residential buildings. While the architectural work focuses on integrating two units into a cohesive residence, the process also involves specific regulatory steps required by the city. These projects require architectural design, construction permits, and coordination with building management. Beyond the physical work of connecting the apartments, the project must also comply with regulatory requirements established by the Department of Buildings.
When condominium apartments are combined in New York City, the Department of Buildings requires the units to be merged into a single tax lot. This requirement is established in Technical Policy and Procedure Notice (TPPN) #3/97, which governs the combination of dwelling units. As a result, a condo apartment combination is not simply a construction project but also a legal process that aligns the physical apartment with the city’s property records.
As an architect working on high-end apartment renovations in New York City, these regulatory requirements are an important part of evaluating condo combination projects. Architectural planning for an apartment combination often begins with determining how the units can be legally combined, what filings are required, and how the design can comply with applicable building regulations. Establishing these parameters early helps guide the architectural planning process and supports the development of a cohesive custom residence. For a deeper discussion of apartment combinations, see our article on Combining Apartments in NYC.
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What Is a Tax Lot in a New York City Condominium
A tax lot is a legal property designation used by New York City to identify properties for taxation and municipal records.
In a condominium building, each apartment is typically assigned its own tax lot. Even though the units exist within the same building, they are legally treated as separate properties.
Each tax lot generally has:
- Its own property tax bill
- A unique identification number within the city tax map
Because condominium apartments are separate legal properties, combining units through construction does not automatically merge their tax lots.
What Is a Tax Lot Merger
A tax lot merger is the legal process of combining two or more tax lots into a single property designation with the New York City Department of Finance (DOF).
When a tax lot merger occurs for condominium apartments:
- The combined residence becomes a single legal property
- The city records reflect one tax lot instead of multiple units
- Property taxes are typically issued as one consolidated bill
A tax lot merger aligns the legal structure of the property with the physical layout of the combined apartment.
DOB Requirements for Combining Condominium Apartments
Apartment combinations in New York City are addressed in Technical Policy and Procedure Notice (TPPN) #3/97, issued by the Department of Buildings (DOB). The notice outlines several conditions related to apartment combinations, including provisions addressing light and air requirements, building egress, kitchen removal, and tax lot changes for condominium units.
One provision of TPPN 3/97 that is particularly important for condominium combinations is the requirement that a new tentative tax lot number be obtained from the Department of Finance prior to DOB approval of the apartment combination filing. This requirement ensures that the newly combined condominium unit is recognized as a single property within the city’s tax records.
Merging Tax Lots at DOF
The tax lot merger process in New York City occurs in two steps and involves coordination between the architect, the Department of Buildings, and the New York City Department of Finance.
The first step is obtaining a tentative tax lot number from the Department of Finance (DOF). This is prepared by an architect through an RP-602C filing. The tentative tax lot documentation must be signed by the Department of Finance and submitted to the Department of Buildings prior to DOB approval of the apartment combination filing. DOB approval is required before the contractor can obtain construction permits.
At this stage the property is not yet legally merged into a single tax lot. The tentative tax lot simply establishes the future tax lot designation for the combined condominium unit.
The second step occurs after construction is completed and the apartments have been physically combined. At that time, the architect submits drawings and documentation to the Department of Finance. The plans must follow DOF standards for tax lot mergers. The Department of Finance reviews the submission and, upon approval, the tax lot merger is finalized and the combined condominium unit is recorded as a single tax lot.
Why Owners Merge Tax Lots When Combining Condo Apartments
Owners pursue tax lot mergers for several practical reasons.
Simplified Ownership Records
The combined apartment is recognized as a single legal property.
Single Property Tax Bill
The owner typically receives one property tax bill instead of separate bills for each apartment.
Resale Clarity
A legally unified apartment can be easier to sell. Buyers often prefer a property that is recognized as a single condominium unit rather than two units connected through construction.
Alignment Between Legal and Physical Layout
A tax lot merger ensures the legal property records reflect the actual configuration of the residence.
Required by DOB
For condominium apartment combinations, the Department of Buildings requires documentation for a new tentative tax lot as part of the filing process under TPPN 3/97.
Architectural and Filing Considerations
Aside from approvals and tax lot mergers the physical combination of apartments requires architectural design, planning, and building permits.
Apartment combinations require filing construction documents with the New York City Department of Buildings. If structural work is involved, the project may also require engineering review and additional approvals.
From an architectural perspective, the goal of an apartment combination is to transform two separate units into a cohesive home with a logical layout and integrated circulation. The home should feel as though it was always one thoughtfully planned residence.
Planning a Condominium Apartment Combination in New York City
Combining condominium apartments in New York City involves both architectural design and administrative coordination.
Early planning for an apartment combination can help clarify:
- Whether the apartments can be physically combined
- What approvals are required
- Whether a tax lot merger is necessary
At Fontan Architecture, we design apartment combinations and residential renovations throughout New York City. Our work integrates architecture and interior design as a unified discipline, allowing the layout, materials, and spatial composition of a home to be developed as a cohesive architectural whole.
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Jorge Fontan, AIA, is an architect and founder of Fontan Architecture based in New York City. The firm focuses on residential design, including new homes and extensive renovations for discerning clients. Through collaborative dialogue that draws on the individuality of each client, projects develop as distinct architectural responses guided by thoughtful planning, precise detailing, and a commitment to creating enduring value.
