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Combining two apartments is a building, approvals, and systems question before it becomes a construction plan. Start by understanding what the existing records and professionals need to confirm.
A useful starting point
01
Combining two apartments means creating one unit from two. It is not only a wall opening: the work can change the layout, connect or reorganize systems, and affect how the combined home is described in building and occupancy records.
See the Manhattan condo renovation context ↗02
This typically involves a change in use/occupancy/egress classification (ALT-1). ALT-1 = change in use/occupancy/egress. A CO is required for changes in use/egress/occupancy, so the existing records and proposed work need to be reviewed together. The correct filing classification is determined by a licensed design professional and the DOB, not by Corniel.
Read the DOB and permits guide ↗03
Co-op boards and condo associations commonly require drawings, alteration agreement terms, insurance documentation, and protection plans before work can begin. Board consent is a gating item, and the building’s own process controls the review.
Understand board approvals and alteration agreements ↗04
An opening between units may require structural analysis. The combined footprint can also require coordination of electrical, plumbing, and HVAC systems across both apartments. The design team and building records establish what is possible and what needs further review.
Read about planning and architect coordination ↗05
The finished plan may involve a kitchen or bathroom reconfiguration, new circulation between the former units, and consolidation of electrical, plumbing, or HVAC systems. The exact scope follows the existing conditions, approved design, and building requirements.
See the full-gut renovation planning context ↗06
An early review of structure, apartment stacks, records, and system capacity can surface important questions before commitments are made. It helps organize the next professional and building reviews, but it does not guarantee an approval, a filing outcome, or a construction result.
Explore the feasibility review ↗07
A co-op or condo’s governing documents, alteration agreement, board review, and managing-agent process can shape the sequence before design is finalized. Bring the building’s actual requirements into the first conversation rather than assuming two neighboring units follow the same path.
Review the Manhattan co-op renovation context ↗Questions worth asking
Often, but it depends on the building, board, existing conditions, and DOB-related review. There is no guarantee that a proposed combination will be approved or feasible.
A change in use/occupancy/egress may require CO action. The filing path and whether CO action is required are determined by a licensed design professional and the DOB.
That is building-dependent. The alteration agreement and the board’s review process govern the request, and board consent is a gating item.
That is beyond the scope of this guide. Consult the appropriate mortgage, insurance, legal, and other professionals about your circumstances.
Planning to combine two apartments?
Share the building, unit relationship, and rough scope you are considering. The first conversation can help organize the questions for the board, design team, and building professionals.
Corniel Construction
Manhattan renovation guidance
Rules-based prototype · not production-approved
