How Much Does it Cost to Combine Apartments in NYC?

An apartment combination may be the easiest way to double your space in NYC—but at what cost?

You may be surprised to learn that a standard apartment combination is not too different from a gut renovation.

Planning ahead is the key to understanding the full scope of your project and the associated costs. When a project is planned appropriately from the start, the areas where there may be a price increase are highlighted by the team. Most commonly, this includes asbestos, structural engineering, or electrical updates.

While gut renovations in New York City typically run anywhere from $216 to $526 per square foot depending on the level of luxury and craftsmanship involved, there are some other variables to consider when combining apartments that can drive the project to the higher end of that range.

Here are the most common factors that can influence the cost of your apartment combination.

Vertical vs. Adjacent Combination

There are two types of apartment combinations: vertical (also called a duplex) where one apartment sits on top of the other; and adjacent, in which the apartments are side-by-side on the same floor.

A vertical combination will be much more expensive than an adjacent apartment combination, simply because they are more complicated and require extra consideration. A vertical combination adds negotiation time with your building, planning time, cost for steel, fireproofing, and inspections.

Serious structural work is typically necessary, such as building a staircase, adding beams, or restructuring beams. Plus, you’re going to want those stairs to look amazing after going to all that trouble, so you’ll probably want to spend a little there, as well! The project will also likely necessitate demolishing floors, as well as putting in new steel, which homeowners will likely need to hire a structural engineer to handle.

Adjacent renovations, on the other hand, can be as simple as popping a hole in the wall and removing the stove, as NYC apartments can legally only have one kitchen.

All told, a vertical combination can add $30,000 to $100,000 to your project.

Architect fees

Apartment combinations nearly always require an architect—an experienced one who will be able to handle the whole scope of the project, from bidding through overseeing the job’s management.

From a basic code compliance perspective, your architect will be required to provide documents to file a combination with the city.

More importantly, an architect’s vision and experience with these types of projects can pave the way to a successful combination. It seldom makes sense to just knock down one wall—combining apartments usually requires some rearrangement of the parts in either unit.

Architects plan the layout and take into consideration things that homeowners usually miss on their own, including outside views, accessibility, circulation flow, storage, and egress. This ensures that the finished apartment looks seamless and natural. A good architect can also often integrate interior design for a more efficient process and synthesized look.

Expect to pay anywhere from 10 to 20 percent of your project’s total cost (including labor, materials and appliances) depending on your architect’s skill and level of experience.

Kitchen demolition

As mentioned above, if both apartments have a kitchen, you have to get rid of one. On the bright side, this can present exciting opportunities to change the flow of space and consider new floor plans. 

A kitchen demolition runs anywhere from $5,000 to $8,000.

HVAC system

If your building allows it, you will probably want to install an HVAC system for central air conditioning.

 At the new price point your combined apartments will command, it’s an amenity future buyers may expect as they compare your home to similarly-priced but more modern condominiums. While some air conditioning companies provide an in-house engineer to install it, it’s recommended that you hire a mechanical engineer for the job to ensure it’s well-integrated and takes up less space.

Expect to pay around $40,000 to $80,000 excluding carpentry expenses to make the HVAC system disappear into the aesthetics of your apartment.

Gas and plumbing lines

Gas and plumbing line problems are standard for any NYC renovation. The challenges for an apartment combination from this perspective are the same as a gut renovation, except when there are major variances in the condition of the systems (for example, if one of the apartments is in estate condition).  

In vertical renovations, gas and plumbing lines can present challenges when these systems pass through the area of the stair and need to be rerouted.

Plumbing risers are the most expensive thing to move around. If one apartment has a bathroom that lines up to the other apartment’s kitchen, you won’t necessarily be able to blast through the wall to create a giant kitchen or bathroom.  The risers—which begin in the basement and end at the top floor—may serve a whole line of apartments, so building managers often forbid moving them for safety reasons and because in past renovations, they’ve been moved improperly in a way that’s caused problems in the building.

If you are allowed to shift the riser line, it will cost around $10,000 to $15,000.   

New windows

Replacing windows is fairly easy—just keep in mind that if your apartment is in a landmark building, you may need to ensure that your windows conform to landmark preservation rules. (Windows on a public façade must conform to a landmarks-approved window replacement scheme. If it doesn’t, your window supplier will have to submit an application to Landmarks showing how the new window design closely reflects the existing conditions.)

Creating a new window opening in a wall is often an option, too, in older buildings that have side or rear exposure to take advantage of. (You’ll need a skilled architect to help win board approval for this; expect to pay around $3,000 for the new opening.) 

The total cost is generally around $1,500 to $3,000 per window.


Millwork will probably be the largest expense in a gut renovation budget, and can vary significantly depending on the level of quality you’re seeking. The cost of millwork ranges enormously depending on the type of wood, veneer, and how elaborate the interiors are divided and broken up into drawers, shelves, etc.

You’ll want to make sure the apartments blend seamlessly, which almost always requires updates to trim, moldings, doors and windows. You should also consider your cabinetry, including any built-ins.

Custom or semi-custom millwork requires skilled labor, and can get quite pricey—but such details can make a space feel much larger.

For high-end custom millwork, prices can range from $200 per linear foot to $800 per linear foot (this is assuming full height bookcases, storage, cabinets, or elaborate wall panels).

Change orders

Change orders are last-minute changes to the project that can add up to 10 percent of its total cost—but these 11th hour alterations are almost always initiated by homeowners.

While many people recommend setting aside 20 percent extra to include "surprises," this shouldn’t happen if a competent architect and general contractor are involved who do adequate due diligence beforehand.

Extra costs to look out for

Unexpected costs can add up, and there are a few you should look out for.

You’ll need an expeditor ($1,000 to $3,000 depending upon level of service) to help navigate city bureaucracy. Along those lines, you will also have to pay fees for city permits and asbestos inspections (the latter may require a third party monitor, if a significant amount of asbestos is found).

There will probably also be a number of payments to make to your building for the protection of hallways, doors, and elevators ($800 is not unusual), for any water or gas shut offs a renovation requires (some buildings charge $500 per shutoff, while others charge nothing), a general construction charge to the building (anywhere from $2,000-$6,000 per month or a percentage of your total construction costs), and penalties for going over the scheduled renovation time ($50-$200 or more per day).

Final cost

Based on the data we’ve collected about NYC apartment combinations, the average cost per square foot is $388. Projects of this type take an average of five to eight months in the design phase, and 6.5 to seven months in the build phase.

About Us

Bolster is a data-driven team of experts on a mission to eliminate risk from major home renovations by being radically transparent across everything we do. We hire the industry’s best talent and use a continual improvement process to financially guarantee that your major home renovation is designed and built beautifully, on-time and on-budget. From the first sketch to the final handshake, our homeowners know the cost of every line item and have full visibility into project milestones.