True Cost Guide Architects & Engineers Build a Duplex

How Much Does It Cost to Build a Duplex?

Typical Range:

$142,500 - $1,100,000

Cost data is based on research by HomeAdvisor.

Updated April 4, 2022

Reviewed by Ezra Laniado, Expert Contributor.

Written by HomeAdvisor.

The cost to build a duplex varies between $142,000 and $1,100,000. The average cost is $388,000. This significant variance in cost is due to the potential differences in the size and style of the duplex you choose. Although duplexes share many common attributes, they vary substantially in size, space, style, finish, and location, which all influence the cost to build one.

Average Cost to Build a Duplex

Low Cost	$142,500
Average Cost	$388,000
High Cost	$1,100,000

Building a Duplex Labor Prices

When you're building a duplex, you're taking on a substantial project that requires the skills of many different professionals. Take a look at this breakdown and see exactly where your budget goes on a project of this magnitude.

Project	Percentage of Project Cost
Cost to hire an architect	10% – 15%
Cost to hire a structural engineer	$500 – $20,000
Cost to hire a general contractor	25%
Cost to lay the foundation	8% – 10%
Cost of framing a house	10% – 12%
Cost to erect walls and finish the exterior	6% – 10%
Cost to build a roof	8% – 12%
Cost to install windows and doors	3% – 7%
Cost to finish the interior	6% – 10%
Cost to lay flooring	3% – 5%
Cost to install interior features	3% – 5%
Cost to install a bathroom	3% – 5%
Cost to install a kitchen	6% – 10%
Cost to hire an electrician	8% – 12%
Cost to hire a plumber	10% – 14%

Cost to Build a Duplex by Size

Building a duplex is a complex project that entails a lot of different components and many different professions. The cost to build a duplex varies from $95 to $220 per square foot, with a national average cost per square foot of $130, including parts and labor.

Duplex Size in Square Feet	Cost Range (All-In)	Average Cost (All-In)
1,000 sq. ft.	$95,000 – $220,000	$157,500
2,000 sq. ft.	$190,000 – $440,000	$315,000
3,000 sq. ft.	$285,000 – $660,000	$472,500
4,000 sq. ft.	$380,000 – $880,000	$630,000
5,000 sq. ft.	$475,000 – $1,100,000	$787,500

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Cost to Build a Duplex by Type

There are three main types of duplex, and each carries a different price per square foot. At the lower end, you've got the one up, one down style duplex in a stacked configuration. At the higher end, the two-story side-by-side duplex, and in the middle, the one-story side-by-side style.

Duplex Type	Cost Range (All-In)	Average Cost (All-In)
Stacked (one up, one down)	$95 – $135 per sq. ft.	$115 per sq. ft.
One-story side-by-side	$110 – $180 per sq. ft.	$145 per sq. ft.
Two-story side-by-side	$130 – $120 per sq. ft.	$175 per sq. ft.

Stacked One-Up, One-Down Duplex

One up, one down duplexes cost an average of $115 per square foot, including parts and labor. You can pay as little as $95 or as much as $135 per square foot, depending on materials and location.

A stacked duplex features one apartment on top of another, usually with the same amenities and layout. While usually not as spacious as side-by-sides, stacked duplexes are the least expensive to build and require the least amount of space.

Additionally, you reduce your costs with a stacked duplex because you need less roofing and a smaller foundation. Plus, you'll need less wiring and pipework because they can be centralized and shared easier.

One-Story Side-by-Side Duplex

The cost of a one-story duplex is $110 to $180 per square foot, all-in, with an average price of $145 per square foot.

A single-story duplex features two one-story apartments side by side, instead of stacked, each only on one level. With this configuration, the duplex has a larger footprint and requires more roofing and a bigger foundation, which adds to the total project cost.

Additionally, the plumbing and wiring are decentralized, requiring more work and more materials, further increasing costs.

Two-Story Side-by-Side Duplex

A two-story side-by-side duplex costs $130 to $220 per square foot for parts, materials, and labor. The average cost is $175 per square foot. Each half of the duplex has two floors and shares a roof and foundation.

Like single-floor side-by-sides, they require larger foundations and roofs, and the plumbing and electrics aren't centralized, which pushes up the cost. However, they are more spacious, have more square footage, and command a higher rental or resale price.

Cost to Convert a Single Family to a Duplex

If you have an existing single-family property and want to convert it to a duplex, expect to pay between $80,000 and $100,000. Not all homes can be converted into duplexes.

For example, if the home cannot be portioned off into two equal-sized living areas or the property isn't zoned for a multi-family building, then it's not possible to move ahead with the conversion.

However, if the property does meet all the necessary criteria, then a conversion is possible. But remember that there is still a significant amount of work involved. Rewiring, HVAC rerouting, plumbing installations, adding a new kitchen and bathroom, and more all need to be factored in.

Factors That Influence the Cost to Build a Duplex

Aside from location, style, and size, there are numerous other factors that influence the cost to build a duplex.

Demolishing an Existing Property

If there is an existing property on the lot that isn't suitable for conversion, you need to factor in demolition costs. The cost to demolish a house is between $3,000 and $25,000, with an average cost of $18,000.

If the existing property has asbestos, you'll need a licensed hazardous waste contractor to remove it. The cost to eliminate asbestos is around $2,000.

Interior Designer

If you want to individualize the interior of each half of the property, you can hire an interior designer. The cost to hire an interior designer is $50 to $200 per hour. While not essential, the services of an interior designer can elevate and enhance a space.

Attached Garage

Adding attached garages to each half of a duplex enhances the appearance, adds value, and increases vehicle security. The cost to build a garage is between $10,000 and $27,000 per garage for a single-vehicle unit. For a double-vehicle garage, expect to pay between $15,000 and $40,000 per garage.

Smart Home

Creating a smart home costs $200 to $3,000, with an average cost of $1,600. Home automation is a luxury feature that increases property value and adds a superior level of convenience.

You don't have to automate the entire home, but adding a smart thermostat, smart lighting, smart sockets, and similar features can also help make your home more energy-efficient by reducing energy waste, lowering your home's carbon footprint, and shaving dollars off your utility costs.

DIY vs. Hiring a Duplex Building Pro

Because building a duplex requires so many different skills, it's not practical to attempt it yourself. However, there are some tasks you can tackle to reduce the project cost if you have the necessary time and skill.

Some people think they can save up to 25% of the project price by going without a general contractor. However, these professionals are worth their weight in gold. They manage the whole project for you, pulling in more labor and the right pros at the right time to get the project completed on time and on budget.

They have to juggle a lot of moving parts and communicate at all levels. While you can, theoretically, manage without a general contractor, it adds a huge amount of work and responsibility and can lead to missed deadlines, overspending, and many problems.

If you really want to save and you've got some DIY skills, you can cut costs by doing a lot of the interior finishing yourself. With the right skills, you can lay flooring, paint walls and ceilings, and install crown molding and other finishing touches.

Alternatively, you can leave the entire project in the hands of the pros and save yourself a lot of headaches.

FAQs

Is a duplex multi-family?

Yes, a duplex is a multi-family property containing two individual dwellings.

What's the difference between a duplex and an apartment?

The main difference between an apartment and a duplex is that a duplex consists of only two individual dwellings within a single structure, while an apartment may be part of a much larger collection of dwellings.

In a duplex, you only have to share one wall or ceiling with a neighbor, whereas in an apartment, you'll likely share walls and floors or ceilings with multiple other residences.