Combining Apartments: A Guide to the Process (Part 1)


(Above) Combined apartment renovation by Sweeten architect, Slavica. “After” photos: Emily Sidoti

Apartment dwellers are known for their ability to make the most of small spaces. But there may come a time when even the most resourceful homeowner runs into challenges that only additional square footage can solve.

What do you do when you need more room? You can head for the suburbs, search for a larger apartment in another locale, or if you’re lucky, scoop up an adjacent apartment and hold onto everything you love about your current spot while enlarging your home footprint. Another enticing option is searching for a new combination opportunity in a new neighborhood with a large inventory of smaller apartments and a growing demand for family homes.

How Sweeten Works

cosenza plan BEFORE

cosenza plan AFTER

(Above) Combined apartment floorplans for Upper East Side project by Sweeten architect Slavica

Here, the pros and cons of merging apartments, including key considerations and what you’ll need to know going in, including links to more resources. Be sure to check back next week for Part II, an in-depth look on how to budget for this type of project!


(Above) Guest bathroom in combined apartment project


Combining apartments is not for the faint of heart. In addition to all of the aspects of a single-unit renovation, there are further legal, bureaucratic, financial, and structural considerations when joining units. This Sweeten post on making layout changes covers a few basic considerations. It’s no wonder that when faced with the choice of 1) moving, 2) staying and combining, or 3) moving and combining, most people will opt for the first. But we’ve seen some incredible results that show us it may well be worth the hassle to stay and combine, or “double down.” Let’s first take a look at the pros and cons:


*You stay in the same building and neighborhood, with access to all the same amenities, schools, services, and parks you love.

*It may be more cost effective to buy a smaller unit and pay for a renovation than to buy a new, larger unit.

*You’re already knowledgeable about the building. And if you’re on good terms with your board and super, it may be easier to arrange the bureaucratic and logistical intricacies of a renovation than if you’re the new kid on the block.


*Since you are limited to the immediately adjacent units, the abutting spaces may not be conducive to a smooth flow, depending on layout restrictions. You might end up with awkward hallways or bedrooms off the kitchen.

*The board might be unhappy to have too high a percentage of ownership concentrated in one person’s hands, and in turn, prove difficult about the approval process.

*You will shoulder additional maintenance and taxes, and the combined charges may appear unusually high to potential buyers for resale.

*Similarly, you will have to pay the carrying costs on both apartments for the duration of the renovation (possibly without being able to live in either).

*If you choose to merge two apartments in a new location, you’ll face the same cons, as well as the need to finance two home purchases.


(Above) Dining and media room in combined apartment project


Homeowners with adjacent apartments have the luxury of multiple layout options, but also need to work within a unique set of constraints to create the new space. In any unit-combining project, you’ll have to consider the following questions:

*Is a combination even possible? Not all buildings allow combinations. And in those that do, before you buy, bring in an architect and/or structural engineer to assess whether your dream can be made a reality. Don’t assume that you can knock down that wall! As one Sweeten contractor points out: “Your ability to probe for structural elements prior to construction can be limited by building requirements and existing tenants, and building records are notorious for omitting elements of the building’s composition, so you have to work with your architect to prepare for unforeseen conditions.” Although there is a limit to what can be deduced without actually starting demolition, a consultation will give you a sense of what you can do and how much it’ll cost.

*Are you combining horizontally or vertically? Horizontal is typically easier, because it can be as easy as knocking through a non-structural wall to make a door-sized opening, and removing one kitchen (NYC code only permits one kitchen per apartment, although certain exceptions can be made). Vertical combinations (duplexes) are more complicated because along with structural considerations typically comes more electrical and plumbing systems hidden in floors. And don’t forget the staircase–it can take up more space than anticipated, and require the participation of many experts (architect, structural engineer, contractor, millworker) to design, approve, fabricate, and install.

*Can you use the space intelligently and create an overall flow? Not all combinations are created equal. Buildings often limit where you can move baths and kitchens with “no wet over dry” rules, preferring that wet rooms remain stacked on top of each other from floor to floor (to curtail damage from any potential leaks and preserve plumbing lines). This and other restrictions may create an awkward new layout that isn’t conducive to your lifestyle, even if it gives you the basic square footage you need. Strange layouts are also difficult to market if you ever plan to sell.

*Are the apartments in similar condition, and are the floors and ceilings level? If the two units were updated at different times, they might not share the same flooring, trim, moldings, doors, or hardware. You’ll want to align the fixtures and finishes to create a cohesive look. Apartments in older buildings are sometimes unleveled. Many creative solutions are available, such as sunken living rooms or coffered ceilings, but it’s best to consult an architect on what will work best in your space.

*How will you merge the heating and cooling systems? Especially in older buildings, units may not share the same type of systems. You may consider installing an entirely new system across the new space.


(Above) Kid’s bedroom in a combined apartment project


A renovation is always a learning process, and doubly so when it’s a combination project. You are usually allowed to merge units in either co-ops or condos, but different approvals and filings are associated with each. In both, however, you’ll have to deal with requirements from the building as well as the city.

Building requirements

Get in touch with management to make sure that you have a comprehensive list of all the building requirements. Most buildings will also require architectural plans first be submitted to the board for approval. Some will have template alteration agreements in place, which can be adapted to your specific project. These will have details about permissible work hours, protection of common areas, whether there are “wet over dry” rules, as well as information about the costs associated with approvals, security deposits, and other building fees.

City requirements

A myriad of codes govern apartment combinations, and New York City has put together resources like this one to guide homeowners through the process. Still, you’ll probably want to hire an expediter to help you navigate the labyrinthine process. Unlike simpler renovations, joining units will most certainly require permits from the Department of Buildings (DoB). For example, you’ll need an ALT2 (Alteration Type 2) application for a permit to remove a kitchen, which involves cutting and capping all gas and electrical lines. For condos, you will also need to merge the tax lots on the two properties by filing an amendment to the condo declaration and offering a plan with the Department of Finance (DoF).

A final note on approvals: homeowners tell us that the hold-ups usually occur in the building approval process, rather than with the city. This is because boards can make decisions “as they see fit,” leading to inexplicable delays, whereas the city permits process is well-regulated and navigable by an experienced professional, such as an expediter.


Given the complexity of combination projects, it’s best to add a buffer in terms of time as well as cost overruns (more on this in Part II of this series). Give yourself a few months of wiggle room–if your general contractor says that the project will take six months, plan for it to take eight or nine. Your contractor should be able to tell you at the outset of your project whether it would be advisable or possible for you to stay put. If you need to relocate, rent a space nearby for at least that amount of time so that you’ll have a debris-free home that’s close enough to the construction site for frequent check-ins.

As with most renovation projects, there will be inevitable hiccups and delays. Just remember the prize: a beautiful, sprawling apartment customized just for you and your family to enjoy for years to come.

Be sure to set the right renovation team in place. Here’s our guide on what to look for when working with a general contractor.

Sweeten handpicks the best general contractors to match each project’s location, budget, scope, and style. Follow the blog for renovation ideas and inspiration and when you’re ready to renovate, start your renovation on Sweeten.