The cost to build a duplex varies widely, based on many factors. The average approaches $390,000.
Understanding the nuts and bolts of constructing a brand-new two-unit structure gives a better sense of how much it will cost to build a duplex.
Let’s define duplexes and then examine estimates for building one.
Table of Contents
Key Points
• The cost to build a duplex can vary depending on factors like location, size, materials, and labor.
• On average, the cost to build a duplex ranges from $142,000 to $1,100,000.
• Additional costs to consider include permits, design fees, landscaping, and utility connections.
• Building a duplex can be a good investment opportunity and provide rental income.
• It’s important to work with professionals and create a detailed budget before starting a duplex construction project.
What Is a Duplex?
Duplexes come in different sizes and designs, but they have commonalities, like:
• One building, one lot. The two units are in one building on the same piece of property.
• Common partition. Duplex units have a shared wall or ceiling/floor. Occupants may share the yard space and a laundry room.
• Mirrored size or layout. The two residences in a duplex are often mirror images of each other or the same size.
In general, buying a duplex will cost less than purchasing a stand-alone single-family home in the same area. And it might be cheaper to buy a duplex than build one, although you can customize new construction. Then there are people who convert a single-family home into a duplex. That could cost $80,000 on average.
Duplexes are in demand, thanks to owner-occupant financing advantages and potential rental income. They also can be found among HUD homes for sale. If you are thinking of buying an existing home loan, you may be able to finance your purchase with a home loan. If you have an existing home to leverage for funds to invest in building a duplex, a home equity line of credit (HELOC) could be a suitable financing option.
First-time homebuyers can
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with as little as 3% down.
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Factors That Determine the Cost of Building a Duplex
Plenty of factors influence the cost to build a duplex, with some choices stretching the budget more than others.
Location
In more desirable areas, the plot could really thicken in terms of price. Land prices in the Northeast tend to be the highest, with Rhode Island, New Jersey, and Delaware terra firma the dearest.
Materials and Labor
Depending on supply and demand, the cost of materials and labor can vary dramatically. If there’s a shortage of labor or supplies, duplex builders may pay a premium.
Building a duplex, or any property from the ground up, requires specialized labor, including these pros:
• Architect
• Structural engineer
If the lot has a property on it, the buyer may need to pay to demolish it before building a duplex. If the lot is bare, adding utilities such as plumbing, electricity, and gas will factor into the cost of the build.
Size of the Duplex
In general, the larger the structure, the higher the cost.
The more rooms and the more complicated the layout, the higher the price.
Type of Duplex
The type of duplex a person decides to build can affect the project’s cost. Here’s how the kind of duplex can influence its price tag:
• Stacked ($95 to $135 per square foot). Stacking the units on top of each other will typically be the least expensive build, as it’s the most efficient. Owners may be able to save on labor as the units will mirror each other and save time on plumbing.
• One-story, side-by-side ($110 to $180 per square foot). This is likely a more complex build.
• Two-story, side-by-side ($130 to $220 per square foot). This type of duplex is even more complex and has more square footage than the above options.
Miscellaneous Factors
Depending on the lot purchased or desired features, there could be additional costs associated with the build. Common expenses include:
• Tearing down an existing home. If there’s a property on the lot, it can cost between $7,500 and $15,000 to tear it down.
• Interior design. While not required, hiring an interior designer could help both spaces feel more liveable and comfortable. The average interior designer costs between $75 to $450 an hour.
• Modular duplex. A modular duplex, meaning buying a prefabricated home, costs $100, on average, per square foot.
• Garages. If the duplex owner wants a garage or two attached to the home, they may pay $35,000 more.
How Much Does It Cost to Build a Duplex?
With an understanding of the cost factors that can affect the budget for the duplex, now it’s time to address the big question.
Here are overall costs, then costs based on labor and square footage using up-to-date national averages.
Overall Construction Cost
These are the high-end, low-end, and national averages to build a duplex.
| High end | $1,100,000 |
| Low end | $142,000 |
| Average | $388,000 |
By comparison, building a new house of 2,500 square feet could cost $329,000. The average existing single-family home in the country sold for $402,600 in late 2024.
Labor Cost
A large portion of the budget to build a duplex will go into labor and specialized professionals. Construction workers averaged about $35 per hour in 2024, though there is wide variation by region and type of labor. The overall cost of construction labor has increased steadily for more than a decade.
Cost by Square Foot
Here’s a breakdown of average cost per square foot (including labor) for duplexes:
• 1,000 square feet: $95,000 to $220,000
• 2,000 square feet: $190,000 to $440,000
• 3,000 square feet: $295,000 to $660,000
• 4,000 square feet: $380,000 to $880,000
• 5,000 square feet: $475,000 to $1,100,000
The Takeaway
While building a duplex isn’t that different from building a single-family home, the process does include additional labor and considerations that can sway the budget dramatically. Size, style, and location can influence the cost to build a duplex.
Some people interested in building a new duplex will look for a construction loan, but if you’re a homeowner who’s eligible for a home equity line of credit, that could be a good source of funding.
SoFi now offers flexible HELOCs. Our HELOC options allow you to access up to 90% of your home’s value, or $500,000, at competitively low rates. And the application process is quick and convenient.
FAQ
Is it cheaper to buy or build a duplex?
Given the price of labor and materials, it is often cheaper to buy a duplex than build one from the ground up.
How much do you have to put down to build a duplex?
A construction loan typically requires a 20% to 30% down payment. A HELOC or home equity loan could be used instead if you’re eligible.
How long does it take to build a duplex?
It takes about 12 months on average to build a two- to four-unit residential building, not counting the time it takes to obtain permits, according to the U.S. Census Bureau’s latest Survey of Construction.
Photo credit: iStock/Luckie8
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