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How Much Does It Cost to Build a Duplex?

Low
$127,500
Average Cost
$375,000
High
$1,000,000
(3,000 sq.ft. two-floor side-by-side duplex with mid-grade materials)

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How Much Does It Cost to Build a Duplex?

Low
$127,500
Average Cost
$375,000
High
$1,000,000
(3,000 sq.ft. two-floor side-by-side duplex with mid-grade materials)

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Duplexes are popular investment properties for homeowners who want rental income without the hassle of owning a large, multi-dwelling property. Duplexes come in many shapes and sizes, although they have many attributes in common. The variations in size, style, material, and location lead to a wide range of building costs. The national average cost to build a duplex is between $275,000 and $525,000, with most people paying around $375,000 for a 3,000 sq.ft. side-by-side style duplex with two floors. At the lowest cost, it is possible to build a 1,500 sq.ft. stacked duplex for $127,500. A high-end, single-story side-by-side duplex of 5,000 sq.ft. would cost $1,000,000 to complete.

Cost to Build a Duplex

Duplex Building Costs
National average cost$375,000
Average range$275,000-$525,000
Minimum cost$127,500
Maximum cost$1,000,000


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Build a Duplex Cost by Project Range

Low
$127,500
1,500 sq.ft. stacked duplex with builder-grade materials
Average Cost
$375,000
3,000 sq.ft. two-floor side-by-side duplex with mid-grade materials
High
$1,000,000
5,000 sq.ft. single-story side-by-side duplex with high-end materials

What Is a Duplex House?

A duplex is a multi-family dwelling or type of apartment building. It is part of a group of apartments known as an infill - a stick-built, home-style building that contains 2 - 6 separate apartments. Duplexes have two separate residences, each with an entrance to the outdoors, while triplexes have three residences, and quadrexes have four.

Duplexes are normally laid out side by side but can have one apartment stacked over the other. The two residences have a shared interior wall or floor/ceiling. Typically, a duplex is owned by one person who lives in one half and rents out the other or rents out both halves.

Price per Square Foot to Build a Duplex

Like all infill apartment-style homes, duplexes have a range of associated costs to build. These costs are influenced by location, with some areas having higher construction costs than others, and by the duplex’s materials and style. Side-by-side duplexes tend to be more costly to build than duplexes with one apartment stacked over another. The average cost range to build a duplex is between $85 and $175 a square foot, with most people paying around $150 a square foot for mid-range duplexes.


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Duplex Prices by Type

Duplexes can be laid out in one of two ways. They can be single-story or two-story with the separate apartments laid out beside one another. This is known as a side-by-side layout. They can also be two stories, but each apartment takes up just one floor, with one apartment over the other. This is known as a stacked duplex or a one-up, one-down duplex.

In either case, the two apartments are usually identical in shape, size, and layout, and they each have an entrance to the outdoors.

Both types of duplexes have a range of costs to build, but side-by-side units are usually more costly, regardless of whether they are single or two-story. This is because they have additional costs for roofing, framing, and plumbing that can be negated by putting one apartment on top of another:

Duplex Prices Chart


Duplex TypeAverage Cost per Square Foot
One-Up, One-Down$85 - $125/sq.ft.
One-Story Duplex$100 - $150/sq.ft.
Side-by-Side Duplex$125 - $175/sq.ft.


Two-Story Duplex One Unit Up, One Down

While side-by-side duplexes can also have two stories, a stacked duplex with one apartment above the other is the least expensive building method. Assuming that the square footage remains the same, you reduce the amount of roofing and foundation by putting one apartment above the other. It also makes it easier to centralize pipes and electrical wiring, making the project less costly. The average cost range for this type of duplex is between $85 and $125 a square foot.

One-Story Duplex

A one-story duplex has two apartments side by side, each with only one level. This means that the duplex takes up more space within the lot and needs a larger roof and foundation. For that reason, this type of duplex is more expensive to build than a one-up, one-down duplex, even if the apartments in both types are identical in shape, size, and layout. Expect costs for this duplex style of $100 to $150 a square foot.

Side-by-Side Duplex

The side-by-side duplex is the most common type. In this style, each apartment has two floors, which are mirror images of one another. These duplexes are larger, have more square footage, and are also the most expensive to build. They have the challenges of a one-story, meaning larger roofs and foundations and decentralized plumbing and utilities, while they also have added structural costs for building up. The average cost range for this style of duplex ranges from $125 to $175 a square foot.


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Average Cost to Build a Duplex

Every duplex is a little different in terms of materials, location, and building style. Your exact costs for labor and material vary. It is possible to break down the various components to give a general idea of where your money goes for this project.

Modular Duplex Cost

Modular building is a faster, more efficient method of construction than traditional stick building. The house is built in sections off-site in a factory under controlled conditions. The finished pieces are transported to the jobsite, where they are assembled and finished. The process usually uses more materials and stricter building allowances since the house needs to withstand transport. This means a more durable structure. Because it is built indoors, there are no weather delays, and with computer-aided programs and technology, the build can be done faster for less money.

Modular duplexes are usually at the lower end of the cost spectrum. While the average cost of a stick-built duplex is $150 a square foot, the average cost of a modular duplex is around $100 a square foot for the same building style.


Beautiful brick modular duplex buildings


How Much Land Is Needed for a Duplex?

The exact amount of land you need for a duplex varies, just like it does for a private home. Side-by-side duplexes and single-story duplexes require larger lots than one-up, one-down duplexes, which can take advantage of height to create the square footage.

In general, the total lot should be between 2.5 to 3.5 times the house’s size for a private residence. Because duplexes are shared spaces, you may decide that you do not need as much usable land around the building, or you may decide that you need more land to create separate yards. Either case is acceptable, as long as your building size meets your town or city codes and ordinances for how close it can be to the edges of the lot.

Pros and Cons of Living in a Duplex

Duplex living has a lot of positives and negatives to consider. If you own the duplex, living in one side and renting out the other provides a stream of income and helps pay the mortgage. Doing so means you live side by side with your tenant, making you always on-site for repairs and complaints.

Even if both you and the other resident rent, this can mean a lot of forced time interacting with one another about the property. If the other resident is a family member or friend, this can be beneficial. If it is someone you do not get along with, this can be a difficult experience.

Duplexes have shared roofs, foundations, and other areas. This means that any need for repair impacts the entire building and both residences at the same time. If it is not your side with an issue, you still need to deal with it on at least some level.

However, with many people living in multi-family dwellings, duplexes mean that you only have one other family to deal with, rather than several, making for a relaxed living atmosphere.


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Average Cost to Convert a Single Family to Duplex

Converting a single-family home to a duplex can have many benefits, such as being able to house a family member or friend while giving them some privacy or having a space to rent for additional income.

Not all homes are eligible for this type of conversion, however. Some are not laid out in a way that makes sense - a duplex has two, equal-sized living areas, and some homes cannot be cut this way. Some homes are also not zoned for multi-family buildings and cannot be legally converted.

If your home meets the above conditions, be prepared to work. Plumbing, HVAC, and electricity need to be rerouted. The new apartment needs a kitchen, bathroom(s), and a separate entrance. You also need to divide the spaces properly. The average cost of a conversion is between $80,000 and $100,000 by the time all these conditions are met, depending on the project’s size.


Semi-detached duplex house and garden


Cost to Build a Triplex

A triplex is a single building with three separate residences inside. This is also an infill apartment building like a duplex, but it is larger. Usually in a triplex, the three apartments are one over the other, rather than side by side, but some side-by-side designs work. The average cost to build per square foot is the same basic range as a duplex - $85 to $175 a square foot, depending on the location, materials, and layout.

The average triplex costs around $750,000 to build, assuming a three-story building, with all three units having the same layout and amenities.

Duplex vs Triplex

Both duplexes and triplexes fall under the category of an infill apartment, or a residential, multi-family dwelling that is “stick-built” or that uses traditional house construction for its build. Duplexes have two apartments, while triplexes have three. Duplexes are most commonly laid out side by side, while triplexes are most commonly laid out in three stories. They have similar costs to build per square foot and can often be zoned in the same areas.

Cost to Build a Fourplex

A fourplex or a quadplex is another infill apartment building. This type of multi-family dwelling is usually laid out similarly to a side-by-side duplex, but each half of the house has two apartments, one located over the other. Fourplexes have the same basic cost range to build as other infill apartments - $85 to $175 a square foot, depending on the location, materials, and layout. The average fourplex costs around $1,200,000, with all four units having the same layout and amenities.

Duplex vs Fourplex

Both duplexes and fourplexes are infill apartments that are laid out similarly. The biggest difference is that duplexes have a direct entrance to each apartment from the outdoors. At the same time, in a fourplex, there are two direct exits to the outdoors, and each entry leads to interior entrances to the two apartments. This means that there is more shared space in a fourplex than in a duplex, where the living is closer to that of a single-family home. They have similar costs to build per square foot and are often zoned in the same areas.

Is It Cheaper to Build a Duplex than Two Houses?

Many people build duplexes to have an income stream from renting one half. Others build duplexes to house a family member or friend while retaining some privacy. Building another house on an adjoining lot could do many of the same things, but building two houses is much more expensive than building a duplex.

Duplexes have one roof, one foundation, and one general exterior structure. Because they have two kitchens and living areas, they are more costly to build than a single-family home of the same size, but not by that much. If you were to build two separate homes, you would have two separate foundations, two separate roofs, and two separate wall structures. This costs significantly more to build than to install a second kitchen and to divide the layout of the duplex into two equal spaces.

If you are looking for a way to build two residences, building a duplex costs about 63% the cost of two single-family homes. In addition, two single-family homes need two separate lots of land, while a duplex can be built on one. Land is often a considerable expense that adds to the property’s value and cost, which makes building a duplex a strong financial choice.

Duplex vs Townhouse

Duplexes and townhouses both offer side-by-side living spaces with shared walls. But while a duplex is a single building divided into two separate residences, both usually owned by one person, a townhouse is a group of 4 or more residences with shared walls. Townhouses are usually owned individually, making them closer to condos than to duplexes despite the shared wall layout. In a townhouse, each owner helps offset some of the maintenance costs for the overall structure, while each unit pays its own expenses. In a duplex, the entire property is owned as one, with one or both units being rented out.


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Enhancements and Improvement Costs

Interior Designer

Interior designers make the most of the layout in each half of the duplex. This is useful for individualizing the spaces and making them both work for their residents. The average cost to hire an interior designer is $75 to $450 an hour.

Attached Garage

It is very common for each side of the duplex to have an attached one-car garage, and larger duplexes may have two-car garages. The average cost to add an attached garage is around $35,000.

Additional Considerations and Costs

  • If there is already a structure on the lot you intend to build on, remodeling it into a duplex can save you money because tearing it down and removing it increases costs.
  • Maintenance for duplexes is often tax-deductible because it is an income property. This includes things like yard work and regular ongoing maintenance for both units.
  • Duplexes and “semi-detached” houses are the same. They refer to a single building divided into two equal living areas but are detached from a row of houses like a townhouse.
  • Duplexes usually have the same address, with one side being labeled as apartment A or 1 and the other B or 2.
  • In some areas, you can find a single building divided into two residences where each side is deeded separately. These are known as halfplexes or condexes, and they are treated like condos, where each owner maintains their side. However, they share expenses for general exterior maintenance and repair.

FAQs

  • How much does it cost to build a fourplex?

Fourplexes cost between $85 and $175 a square foot to build, with the average fourplex costing around $1,200,000 in total costs.

  • What is the difference between a duplex and an apartment?

A duplex is a subset of apartment building types, specifically in “infill” apartments. While some apartment buildings have many units, a duplex only contains two.

  • How much does a modular duplex cost?

Modular duplexes have an average cost to build of around $100 a square foot.

  • How many bedrooms are in a duplex?

Duplexes come in many sizes. They may have one, two, or three bedrooms in each half.

  • Is a duplex multi-family?

Yes, a duplex is considered a multi-family dwelling, consisting of two apartments.

Cost to build a duplex varies greatly by region (and even by zip code). To get free estimates from local contractors, please indicate yours.

Updated:
The information provided by our cost guides comes from a great variety of sources, including specialized publications and websites, cost studies, U.S. associations, reports from the U.S. government, contractors and subcontractors, material suppliers, material price services, and other vendor websites. For more information, read our Methodology and sources.
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Cost to build a duplex varies greatly by region (and even by zip code). To get free estimates from local contractors, please indicate yours.

The information provided by our cost guides comes from a great variety of sources, including specialized publications and websites, cost studies, U.S. associations, reports from the U.S. government, contractors and subcontractors, material suppliers, material price services, and other vendor websites. For more information, read our Methodology and sources.