We break down exactly what is a duplex apartment in some of the country's hottest rental markets.

Duplex apartments combine the convenience of an apartment and the privacy of a traditional house.

But what is a duplex exactly, and what should your expectation be when you see “duplex for rent" in a listing? In fact, there are multiple definitions for a duplex house or apartment. It all depends on who you ask and where you live.

The common definition of duplex

The most common and general definition of a duplex in most of the U.S. is two separate single-family units in one building on a single lot, often house-like, connected by a shared wall or floor and with separate entrances to the outside.

This, to most, is the definition of both a duplex house because of the style of the unit as well as a duplex apartment as it is a rental.

Duplexes can be side-by-side or up/down, where each floor is a distinct unit.

A New York duplex apartment

In New York City, there is a much different definition of a duplex for rent.

A Manhattan duplex is often a single-occupancy apartment in a tall building spread over two floors connected by an indoor (often spiral) staircase. These are considered duplex apartments, which are in many ways the opposite of a duplex house.

And while multi-family unit duplexes are an affordable option for those seeking a home-like experience, Manhattan single-unit duplexes — which are even sometimes penthouses — can often be some of the most expensive rental property in the city.

These units are frequent in neighborhoods like Tribeca, NoHo, Chelsea, West Village and the Meatpacking District, as well as along Fifth Avenue and Central Park West. This definition is also commonplace in Chicago's loop and areas surrounding downtown.

The Manhattan duplex is also sometimes referred to as a maisonette. Although the word is French for “little house," it has come to be used (no one is exactly sure how) to refer to an apartment within a larger structure. In general, it's a ground-floor apartment with its own entrance. In New York City, the maisonette usually has two floors. Hence the use of the term “duplex" in an apartment building.

What else is a duplex?

Some other U.S. cities have very specific definitions for duplex rentals.

In Dallas, it is “two-dwelling units located on a lot." Philadelphia's definition is “a dwelling occupied as the residence of two families under one roof, each family occupying a single unit."

And conversely, some cities have different terms for the traditional definition of a duplex, including San Francisco where a duplex is officially called a “two-family dwelling" and in rust belt cities like Buffalo and Detroit where you'll see the term “two-flat."

In Canada, many large cities specifically define a duplex house only as a two-family dwelling with one unit above the other with separate entrances. In other words, two floors and not side-by-side units.

The difference between a duplex and an apartment

An apartment is typically found in a building with lots of other units. If you live in one, you might share walls, floor and ceiling with a neighbor.

In a duplex — not one in New York City, as noted — you'll only share one a wall (if it's a side-by-side) or your ceiling or floor (in an up and down).

The biggest difference, though, is that a single property owner owns the structure housing the duplex apartments. The landlord may live in one of the apartments or may rent out both apartments.

Duplex apartments also differ from other apartments in their amenities. Although the average duplex is about 1,000 square feet — about the same size as the average two-bedroom apartment — it feels more like living in a house.

Inside, they have all the rooms one would expect from an apartment or home, but often feature amenities a little less common in apartment buildings or complexes such as in-unit laundry, porches and patios, backyards, driveways and occasionally garages.

The pros of renting a duplex apartment

Here are some reasons to consider renting a duplex:

• It may allow you to live in a pricier residential neighborhood than you might otherwise be able to afford
• You have access to amenities you might not have in a typical apartment building
• You'll only have to share one wall with your neighbor
• It might be quieter than living in a multi-family apartment building
• You'll most likely have more space inside a duplex apartment than a unit in a traditional apartment building

The cons of renting a duplex apartment

Here are some reasons why a duplex might not be right for you:

• If you're looking for fancy amenities like on-site spas, gyms and doggie runs, you likely won't find them in a duplex apartment
• You might be responsible for things such as lawn mowing and snow removal
• It might be more costly than renting an apartment

You also might want to take into consideration:

• You'll have only one neighbor to contend with. But what if you just don't get along with that neighbor? The good news is that you'll have separate entrances, but you will have to figure out how to get along if there's a shared porch or yard, for example.
• Your landlord might be in the other duplex apartment. This could be a good thing since the landlord will be on hand if something goes wrong. But dealing with an absentee landlord can add a certain layer of stress.
• It might be difficult to find duplex apartments in a city's inner core, which depending on your outlook can be just right or unthinkable

Being a good neighbor

In a duplex apartment, since you're only living in close proximity to one other tenant (or your landlord), you have to be extra careful about things like noise and cleanliness.

In an apartment building, you can blame a loud TV on any number of tenants — not so in the duplex. When you're putting in your furniture, for example, you might consider not placing your TV on the shared wall.

Same for any other shared spaces. If you share a yard or patio, you need to remember to always pick up after yourself.

And you have to be extra considerate if you're going to have a party or if guests will be visiting. Find out in advance if they can park in the driveway and make sure your duplex neighbor knows it might get noisy.

If you share an entryway, make sure your boots and shoes are not tripping hazards, keep it free of toys and clear of snow or ice.

Making your decision

There are many advantages to choosing a duplex apartment, including house-like amenities, yards and privacy. They can offer the affordability of an apartment with the benefits of a home. Unless that is, you live in New York and your duplex is a multimillion-dollar apartment, in which case you'd be happy trading that driveway for an incredible Central Park view.