Table of Contents
- Feasibility comes first: ownership, board consent, structure, shafts and stacks decide whether a combination is possible.
- Expect board approval, an alteration agreement and a DOB filing by a registered architect or engineer.
- Planning range is roughly $250-$500+ per sq ft all-in, with design and permits adding about 15-25 percent.
- Full combinations commonly take 4-9 months including approvals; landmarked buildings add time and cost.
- Hidden costs include legal fees, board fees, elevator and loading-dock charges, and extra months of carrying costs.
In a city where square footage is the ultimate luxury, buying the unit next door, or the one directly above, is one of the most New York ways to grow. You keep your building, your block and your commute. You get the open kitchen, the second bath, the room for guests. What you also get is one of the most complicated residential projects in the city: two legal units becoming one, a board with opinions, a Department of Buildings filing, and a wall that may or may not be carrying the floors above.
This guide covers the questions in the order they arise: can it be done, who has to say yes, what it will cost, how it will be designed, how long it will take and what to watch for along the way. Figures are 2026 planning ranges as of October 2026, and a written, itemized quote governs the real price. Rules vary by building, so confirm with your design professional, your managing agent and the agencies named below.
1. The First Question: Is a Combination Even Possible?
Before design or contractors, answer five questions.
- Do you control both units? You need ownership or a binding contract on both. Lenders, title and co-op share transfers matter here.
- Will the board or condo association allow it? Some boards welcome combinations; others restrict them. Read the proprietary lease, by-laws or condo declaration.
- What is between the units? A shared wall may be a simple partition, a brick bearing wall or contain risers, flues and shafts.
- What do the floors do? In a vertical combination, a new stair or opening must pass through floor framing or a slab, which requires engineering.
- What do the codes allow? Fire separation, egress, light and ventilation, and elevator rules apply. The unit count changes, and so may the building's records.
Types of combinations
- Horizontal: two units on the same floor, joined through a party wall.
- Vertical: units stacked, joined by a new interior stair.
- Partial: borrowing a room or hallway rather than merging fully.
- Diagonal and multi-unit: rarer, usually in larger buildings or conversions.
Most feasibility studies take place with a design professional and a contractor on site, looking at the wall, the ceiling below and the riser locations.
2. The Gauntlet: Navigating the Approval Process
Approvals happen in layers, and each layer can reshape the plans.
Board or association approval
In a co-op, the board approves the alteration, and often a change to your proprietary lease or share allocation. In a condo, the board approves the alteration, and the declaration governs unit boundaries. Expect to provide:
- Architect or engineer drawings and specifications.
- Contractor credentials and a certificate of insurance.
- A schedule, protection plan and noise plan.
- Fees, deposits and an executed alteration agreement.
- Sometimes a structural peer review or a building-hired engineer at your cost.
Industry reports indicate that DOB reinstated, effective January 26, 2026, a board attestation inside DOB NOW: Build confirming alterations are board-approved. Treat that as reported and confirm the current requirement with the DOB and your managing agent.
Department of Buildings
Most construction in New York City requires a DOB permit. Alterations are filed through DOB NOW: Build by a New York State registered Design Professional (a licensed Professional Engineer or Registered Architect) who acts as Applicant of Record. Joining units typically changes the dwelling unit count, so the application type is chosen by your design professional; an alteration that changes use, egress or occupancy is filed as an Alteration-CO. The DOB's permit guidance explains the types and process.
Landmarks
If the building is landmarked or in a historic district, the Landmarks Preservation Commission may need to approve exterior-visible changes and some interior work. The LPC's application page lists the permit types, including Certificate of No Effect, Permit for Minor Work and Certificate of Appropriateness.
Other considerations
Tax lot and property records may need updating, particularly in condos. A real estate attorney should confirm the legal steps. See our plain-language Do I Need a Permit? page for how permit triggers are described.
3. Budgeting Your Combination: 2026 Cost Breakdown
Combination costs are large because they involve a full gut renovation of one or two units plus the connecting work. Planning ranges as of October 2026:
| Scope level | Typical planning range | What it typically includes |
|---|---|---|
| Cosmetic refresh | $100-$250 per sq ft | Paint, floors, fixtures, limited layout change |
| Mid renovation | $200-$400 per sq ft | New kitchen and baths, flooring, paint, some layout change |
| Full gut renovation | $250-$500+ per sq ft all-in | Demolition, new mechanicals, kitchens, baths, finishes |
| High-end or structural | $500-$1,000 per sq ft | Structural openings, custom millwork, high-end finishes |
On top of construction, design, engineering and permit fees often add roughly 15 to 25 percent. Landmarked buildings often add roughly 15 to 20 percent to time and budget.
Kitchens and baths drive much of the spend. Full bathroom renovations typically run about $30,000-$60,000+ each, and kitchens $25,000-$85,000+. Selective demolition and haul-away typically run $8-$30 per square foot. Tile, flooring and paint choices swing the total: tile installed is roughly $20-$45 per square foot for floors and $30-$80 for bathroom walls and showers; hardwood is about $12-$28 per square foot installed. For tile guidance, see Best Tile for Kitchen Floors in NYC Apartments, and for wall finishing, Skim Coating Cost in NYC Apartments.
For the citywide picture, our What Does a Renovation Cost in NYC in 2026? guide puts these numbers in context.
4. Design and Layout Possibilities
Once feasibility is confirmed, the fun part begins. Common goals include:
- A public wing and a private wing. Kitchen, living and dining in one unit; bedrooms in the other.
- A primary suite. Joining a second unit often allows a real primary bedroom with a bath and closets.
- A dedicated work or guest room. Spaces that do not exist in a one-bedroom.
- A real kitchen. Moving a kitchen into a larger footprint with an island, or rethinking a closed kitchen as open.
- Light. Combining units on corners increases windows and cross-ventilation.
Constraints to design around:
- Wet areas stacking on existing risers.
- Kitchen exhaust paths through the roof or an approved shaft.
- Egress and fire separation between sleeping areas and exits.
- Elevator and corridor doors that can change when a front door is eliminated.
- The preserved character in prewar buildings, such as plaster details, moldings and parquet.
Plaster is a repeat theme in prewar combinations; new openings reveal cracks and patching. Our guide on why paint peels in NYC apartments explains why surfaces fail after construction vibration and how finishing is done to last.
5. Project Timeline: From Dream to Reality
A typical combination moves through these phases. Durations are planning ranges.
| Phase | What happens | Typical duration |
|---|---|---|
| Feasibility and purchase | Review both units, structure, board rules | 2-8 weeks |
| Design | Programming, drawings, structural and MEP design | 1-3 months |
| Approvals | Board review, DOB filing, LPC if applicable | 1-4+ months |
| Pre-construction | Ordering long-lead items, scheduling, deposits | 2-6 weeks (often overlaps approvals) |
| Construction | Demolition, framing, mechanical rough-ins, inspections, finishes | 3-7 months |
| Closeout | Punch list, sign-offs, final paperwork | 2-6 weeks |
Full apartment gut renovations typically take 4 to 9 months including approvals. Landmarked buildings often add 15 to 20 percent to time. Work hours matter too: NYC's Noise Code generally limits construction to weekdays about 7 AM to 6 PM unless an after-hours variance is approved, and many co-ops and condos restrict work further, often to about 9 AM to 5 PM on weekdays. Use the Renovation Timeline Planner to sketch your own sequence.
6. Do Not Forget These Hidden Costs
Many budgets miss items that are not construction.
- Legal fees for both transactions, board documents and lease or declaration amendments.
- Board and managing agent fees, alteration deposits, and engineer review charges.
- Elevator, freight and loading-dock fees, protection of common areas and super or doorman overtime.
- Temporary housing and storage while construction runs.
- Carrying costs for two units during design and construction: maintenance or common charges, taxes and mortgage.
- Utilities. Separate meters, new gas or electric service and Con Edison or National Grid coordination.
- Insurance for contractors and for your own policy.
- Hazardous material testing. Older buildings may contain lead paint, asbestos-containing materials or other hazards; testing and abatement are separate lines.
- Contingency. Ten to twenty percent for surprises is common practice in older buildings.
7. Structural and Mechanical Challenges
This is where combinations are won or lost.
Walls and framing
A party wall might be a hollow partition, a masonry bearing wall or a combination of both. Opening it requires an engineer to design headers, lintels or steel and to coordinate temporary shoring.
Floors
Vertical combinations require a stair opening through framing or slab. Cutting a slab means structural analysis, reinforcement and fire-safing at the opening.
Risers, stacks and shafts
Plumbing stacks, vent lines, gas risers, electric risers and flues often sit in the very wall you want to remove. Moving them is possible but expensive and can require work in other apartments.
Mechanical systems
Two units may mean two meters, two panels, two HVAC systems. Deciding what to merge and what to keep affects capacity and permits. The new Existing Building Code, Local Law 33 of 2026, is scheduled to take effect July 17, 2027 and will govern alteration applications after that date; until then current rules apply. Local Law 102 of 2025 will require residential gas detectors near gas-fed appliances beginning January 1, 2027, which matters if you are specifying a gas range.
Hazardous materials
Old plaster, floor tile and pipe wrap in prewar buildings can contain regulated materials. Testing before demolition is not optional; the EPA's lead RRP rule page covers lead-safe work practices for pre-1978 buildings, and our Gut Renovation in NYC: The Complete 2026 Guide shows where testing fits.
8. Choosing the Right Contractor for a Combination
The contractor you choose for a combination is not just building walls. They are coordinating a board, an architect, an engineer, an expediter, a super and half a dozen trades inside an occupied building. Experience with these constraints separates a project that finishes from one that stalls.
N.Y. Renovation Services is a licensed and insured, in-house design-and-build company based on Staten Island. Our approach to large apartment projects rests on a few things we can say plainly.
- One team from blueprints to the final coat of paint. Demolition, framing, tile, flooring and painting are coordinated under one contract, so there is one schedule to track.
- Paperwork handled. We work with your registered design professional and can handle permitting and co-op or condo board paperwork when you ask us to, including insurance certificates, schedules and protection plans.
- Hazard-aware demolition. We plan testing and abatement before the first wall comes down.
- Sequenced finishes. Tile, flooring and painting are our priority services. They are scheduled so floors are not scuffed by the next trade and wet areas are waterproofed and tested before finishes go in.
- Itemized pricing and change orders. Detailed contracts, no hidden fees, and a written change order for anything that moves the scope.
- A 5 percent pledge. We donate 5 percent of total project cost to a nonprofit of your choice.
The risk in this kind of project is unmanaged surprise. A missed riser, a rejected alteration agreement or a stop-work order can cost months. We are not a substitute for your attorney or architect. We are the builder who keeps the plan honest and the site moving. When you want a second opinion on feasibility or a line-by-line comparison to another bid, request a free estimate. Our Complete Guide to Home Renovation and Manhattan Renovation Services pages describe how we work across the borough.
9. Neighborhoods and ZIP Codes We Serve in Manhattan
Combination projects look different from block to block.
- Hell's Kitchen (10019, 10036): walk-ups and new high-rises with small kitchens and elevator reservations. Walk-up combinations often involve stairs and tight access for materials.
- SoHo (10012, 10013): cast-iron loft condos in the LPC SoHo-Cast Iron Historic District, with wide-plank and tile finishes. Loft combinations deal with high ceilings, column grids and landmark review. See SoHo, Manhattan Co-op & Condo Gut Renovations.
- East Village (10003, 10009): tenement walk-ups and small apartments in rent-stabilized buildings, with tight stair access. Combining here may involve tenant, regulatory and structural complexities. See East Village, Manhattan Co-op & Condo Gut Renovations.
- Gramercy (10010, 10003): pre-war co-ops and Gramercy Park townhouses in an LPC district, where boards are exacting and plaster detail matters.
- Harlem (10026, 10027, 10030, 10037, 10039): brownstones, row houses and pre-war apartments in historic districts, where floor-through combinations and garden-level work are common.
- Washington Heights (10032, 10033, 10040): pre-war elevator buildings and co-ops on steep terrain. Large layouts and generous ceilings make combinations attractive; deliveries can be complicated by grade.
If your building is outside Manhattan, the same principles apply; for context on how we serve other areas, our Staten Island Home Additions: The Complete Guide shows a different approach to growing living space.
10. Next Steps: Get Your Free Estimate
You do not need drawings to start. You need two things: an honest picture of the building and a clear idea of what you want the combined home to do.
- Gather floor plans, the proprietary lease or declaration and any board guidelines.
- Photograph both units, hallways and the shared wall.
- Send your request through our quote form, or call or text (347) 455-1741. Hours are Monday to Saturday, 8:00 AM to 5:00 PM.
- Book a site visit. We review both units, access, building rules and the schedule you want.
- Review an itemized proposal that separates demolition, structure, mechanicals, finishes and project management.
- Decide the next step: design coordination, board submission or a phased plan.
If your project includes a new primary bath, see how we plan wet rooms on our Bathroom Remodeling NYC page. The earlier you bring in a builder, the more reliable your budget becomes.
Safety Note: All work follows OSHA 30 safety and EPA Lead-Safe practices for pre-1978 homes. Check local permit requirements before starting.
James - Lead Renovation Editor. With over 20 years in renovation and construction, James writes and edits our guides. More about James