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Build a Duplex Cost Guide
Updated: August 17, 2022
Duplexes are popular investment properties for homeowners who want rental income without owning a large multi-dwelling property. Duplexes come in many shapes and sizes, although they have many common attributes. 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 $285,000 and $537,000, with most people paying around $388,000 for a 3,000 sq.ft. side-by-side duplex with two floors. At the lowest cost, you can build a 1,500 sq.ft. stacked duplex for $142,500. A 5,000 sq.ft. high-end single-story side-by-side duplex costs $1,100,000 to complete.
Cost to Build a Duplex
|Duplex Construction Costs
|National average cost
2022 Notice: The Effect of the Pandemic on the Duplex Construction Industry
Like many industries, the construction industry has been negatively impacted by the events of the pandemic over the last two years. What began as a lumber shortage has become a volatile fluctuation in the cost and availability of many goods used for construction. This includes many materials used in the buildings of duplexes, including copper and brass, insulation, drywall, lumber, and many plastics.
In addition, the cost of building has risen approximately 4% over the last year, and predictions say that it will continue to climb a further 4% to 7% in 2022. The housing shortage and the housing market are also predicted to remain in high demand in the coming year. This may mean a surge of not only new construction, but also duplexes in particular, which can be used as rental properties. For those looking to build in 2022, it is recommended that you enter a contract sooner rather than later to help lock in costs before they begin to climb. This can also help get your project going faster, in case of future labor shortages or delays.
What Is a Duplex House?
A duplex is a multi-family dwelling or type of apartment building. It is known as an infill - a stick-built, home-style building containing 2 to 6 separate apartments. They have two separate residences, each with an entrance to the outdoors, while triplexes have three residences, and quadrexes have four.
Duplexes are normally side-by-side but can have one apartment stacked. The two residences have a shared interior wall or floor/ceiling. Typically, it is owned by one person who lives in one half and rents the other or rents 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 the location, materials, and style. Side-by-side duplexes are more costly than duplexes with one apartment stacked. The average cost range to build a duplex is between $95 and $220 a square foot. Most people pay around $130 a sq.ft. for mid-range duplexes.
|Average Costs (Labor Included)
|$95,000 - $220,000
|$190,000 - $440,000
|$285,000 - $660,000
|$380,000 - $880,000
|$475,000 - $1,100,000
Duplex Prices by Type
Duplexes can be laid out in one of two ways. They can be separate apartments beside each other with one or two stories. This is a side-by-side layout. It can also be two stories, but each apartment takes one floor, with one apartment over the other. This is a stacked or a one-up, one-down duplex.
The two apartments are usually identical in shape, size, and layout, and they each have an entrance to the outdoors.
Both types 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.
|Average Cost per Square Foot (Labor Included)
|$95 - $135
|$110 - $180
|$130 - $220
Two-Story Duplex One Unit Up, One Down
The average cost range for this type of duplex is between $95 and $135 a square foot. While side-by-side duplexes can have two stories, a stacked duplex with one apartment above the other is the least expensive method. Assuming 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.
Expect costs for one-story duplexes to average $110 to $180 a square foot. It has two apartments side-by-side, each with one level. This means it takes more space and needs a larger roof and foundation. This type 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.
The average cost for a side-by-side duplex ranges from $130 to $220 a square foot. This type is the most common. In this style, each apartment has two floors, which are mirror images. They are larger, have more square footage, and are the most expensive. 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.
Duplex Construction Styles
Duplexes can be built in several styles. Depending on the home, they can be converted from a single-family home into a duplex or are built this way. Some styles can be built as duplexes, while others may have challenges from how they are laid out.
Hampton-style homes are small modern buildings, and the duplex is no different. These two-story homes are built side-by-side as duplexes. Each side usually has a single-car garage to complete the appearance. The Hampton style is designed for luxury living. These homes have gourmet kitchens, studies, and walk-in butler’s pantries. A deep staircase, usually made of oak, is a central feature for reaching the second floor.
Ranch-style duplexes come in as many styles as a ranch home. They are frequently single-story side-by-side duplexes, but they may have two stories as well. Just like a traditional ranch can be split-level or raised, so can the duplexes. A California style is less likely because they are already so spread out that adding another side usually takes too much space. Therefore, the suburban ranch is the most common style for duplexes. Like all ranches, the duplexes have open floor plans and many modern features.
Modern Farmhouse Duplex
The modern farmhouse duplex comes in several styles. Modern farmhouses are a transitional design that embraces some of the components of a traditional farmhouse, with more modern features. The duplexes work the same way. Some are one-up, one-down, while others are side-by-side. It is common to include the wide front porch synonymous with farmhouses and things like porches and balconies for upper stories. Like many modern farmhouses, these homes are typically painted white.
There are many styles of Craftsman homes, and any could be built as a duplex. This includes the four-square, bungalow, and prairie styles. In some cases, the home could be a one-up, one down, such as a converted four square. You could also have a side-by-side single story, with either the bungalow or prairie styles. If the property is large enough, you can create a two-story duplex in the four-square style. This is the most common of the Craftsman styles to create as a duplex. Like all Craftsman homes, these properties have built-in seating, shelves, and cabinetry and prioritize local materials.
Mid-century modern duplexes come in several styles. Mid-century modern homes may be single-story, two-story, or one-and-a-half stories. This means they are usually side-by-side duplexes. Mid-century homes are frequently asymmetrical, making it more difficult to create as a duplex than other styles. Because there is no one single style for this home, you can add characteristics to other duplexes to get parts of the look. This can include using lots of glass, mid-century pillars on a porch, or very clean, spare lines in the design.
Several home styles are categorized as Victorian, and most can be adapted into a duplex style. The most common is to split a larger Victorian into a one-up, one-down duplex. This means the outside still has the unified look of a Victorian with the gingerbread, trim, and somber color palette, while there are two homes inside. It is less common to create a side-by-side Victorian duplex, but it can be done. The key is keeping the two sides perfectly symmetrical and using the same trim throughout. Features like towers and turrets are likely not included in the design.
Colonials are one of the most popular styles. This is true for single-family and duplex. The Colonial can be split into a one-up, one down easily. This means the center “tower” on the front can remain intact, so it keeps the appearance while containing two homes. Another method is to create a side-by-side colonial and widen the “tower” to include two doorways. The doors must be fairly close together, sharing an entrance rather than each having its own.
Labor Costs to Build a Duplex
Every duplex is different in materials, location, and building style. Your exact costs for labor and materials vary. You can break down the various components for a general idea of where your money goes for this project. You may not have all the following costs, and some ranges change depending on the area. Architect, structural engineer, and contractor fees are added to your final costs rather than being already included.
|Percent of Project Cost
|10.5% - 15% of project costs (added)
|Structural Engineer Fees
|$500 - $20,000 as needed (added)
|25% of project costs (added)
|Walls and Exterior Finish
|6% - 10%
|Windows and Doors
|6% - 10%
|3% - 5%
|3% - 5%
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 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 because the house must withstand transport. This means a more durable structure. Because it is built indoors, there are no weather delays, so the build can be done faster for less money with computer-aided programs and technology.
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.
How Much Land Is Needed for a Duplex?
The exact amount of land you need for a duplex varies, just like for a private home. Side-by-side and single-story duplexes require larger lots than one-up, one-down duplexes, which 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 size for a private residence. Because they are shared spaces, you may decide you do not need as much usable land around the building, or you may decide you need more land for separate yards. Either case is acceptable if your building size meets your town or city codes and ordinances for how close it can be to the edges.
Pros and Cons of Living in a Duplex
Duplex living has many positives and negatives to consider. If you own the duplex, living on one side and renting 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 forced time interacting with one another. If the other resident is a family member or friend, this can be beneficial. This can be difficult if it is someone you do not get along with.
Duplexes have shared roofs, foundations, and other areas. This means repairs impact the entire building and both residences at once. If it is not your side with an issue, you still need to deal with it at some level.
However, with many people living in multi-family dwellings, duplexes mean you only have one other family to deal with rather than several. This can make for a relaxed living atmosphere.
Average Cost to Convert a Single Family to a Duplex
Converting a single-family home to a duplex can have many benefits, such as being able to house a family member or friend and give them privacy or having a space to rent for additional income.
Not all homes are eligible for this 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 size.
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 larger. Usually, the three apartments are one over the other in a triplex 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 - $95 to $220 a square foot, depending on the location, materials, and layout.
The average triplex costs around $787,500 to build, assuming a three-story building, with all three units having the same layout and amenities.
Duplex vs Triplex
Duplexes and triplexes fall under the category of an infill apartment or a residential multi-family dwelling that is stick-built or uses traditional house construction. Duplexes have two apartments, while triplexes have three. Duplexes are most commonly laid out side-by-side, while triplexes are most commonly three stories. They have similar costs to build per square foot and can often be zoned in the same areas.
|Average Costs (Labor Included)
|$285,000 - $660,000
|$427,500 - $990,000
Cost to Build a Fourplex
A fourplex or a quadplex is another infill apartment building. This 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 - $95 to $220 a square foot, depending on the location, materials, and layout. The average fourplex costs around $1,050,000, with all four units having the same layout and amenities.
Duplex vs Fourplex
Duplexes and fourplexes are similar infill apartments. The biggest difference is duplexes have a direct entrance to the apartments from the outdoors. In a fourplex, there are only two direct entries, and each entry leads to interior entrances to the two apartments.This means 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.
|Average Costs (Labor Included)
|$285,000 - $660,000
|$570,000 - $1,320,000
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 them 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 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 much. If you build two separate homes, you have two foundations, two roofs, and two wall structures. This costs significantly more to build than to install a second kitchen and to divide the layout into two spaces.
If you are looking for a way to build two residences, building a duplex costs about 63% of the cost of two single-family homes. Two single-family homes need two separate lots, while a duplex can be built on one. Land is often a considerable expense adding to the property’s value and cost, making them a strong financial choice.
Duplex vs Townhouse
Duplexes and townhouses 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 duplexes despite the shared wall layout. Each owner offsets some of the maintenance costs for the overall structure in a townhouse, while each unit pays its expenses. In a duplex, the entire property is owned as one, with one or both units rented out.
|Average Costs (Labor Included)
|$111,000 - $222,000
|$285,000 - $660,000
Enhancement and Improvement Costs
Interior designers make the most of the layout in each half of the duplex. This is useful for individualizing the spaces and making them work for their residents. The average cost to hire an interior designer is $75 to $450 an hour.
It is common for each side 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
- Remodeling. 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. Maintenance for duplexes is often tax-deductible because it is an income property. This includes yard work and regular ongoing maintenance for both units.
- Semi-detached. 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.
- Address. Duplexes usually have the same address, with one side being labeled apartment A or 1 and the other B or 2.
- Condexes. 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 are treated like condos, where each owner maintains their side. However, they share expenses for the general exterior maintenance and repair.
- How much does it cost to build a fourplex?
Fourplexes cost between $95 and $220 a square foot to build, with the average fourplex costing between $570,000 and $1,320,000.
- 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 of around $112 a square foot to build.
- 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.