A duplex provides advantages to both homeowners and investors, offering a solution for multigenerational living or the opportunity for additional income via renting one or both units. These real estate advantages are the prime reasons people are looking at custom duplex construction, but the next question is: how much does it cost?
Let’s explore the building cost of a duplex and set budget expectations for this real estate opportunity.
Average Duplex Building Cost
Building a duplex is a unique real estate opportunity. It allows you to design a custom home for you and your family that suits your needs. At the same time, it’s also a permanent financial option for rental income. Many people turn to building a duplex themselves since they’re generally uncommon outside of densely populated areas.
Generally, the project cost of a duplex build is less than that of a single-family home, the average being between $285,000 and $537,000. The final numbers depend on the location, materials, square footage, and other details we’ll cover further down.
Cost to Build a Duplex by Square Foot
For homeowners, knowing the cost per square foot can be helpful in budgeting. It provides a basis for estimating costs and understanding how changes to the property might affect its overall value. It’s also handy in assessing the value of a property and, as a metric, allows for consistency in pricing.
With that, let’s break down the average cost of building a duplex into square footage:
- According to Home Advisor, the average total cost per square foot of a duplex build is $95-$220.
The price range comes from each square foot’s value depending on the materials used, the cost of labor, and other factors that go into constructing a building. If you have questions on ensuring the cost by square foot in your custom-built duplex is within your budget, contact our Home Consultants to discuss your options.
Cost to Build a Duplex by Type
There is a general idea of a duplex, usually akin to a larger home with two entrances or a townhouse. People are surprised that a duplex comes in different shapes and forms. According to Home Advisor, the building costs by duplex type are:
- Average single-story duplex build cost: $95-$135 per square foot
- Average two-story duplex build cost: $110-$180 per square foot
- Average side-by-side duplex build cost: $130-$220 per square foot
To better understand the square footage cost for each type of duplex, here is what each type entails:
Two-Story One Unit Up, One-Down Duplex
Side-by-side duplexes are the type people tend to think of, and while they can have two stories, a stacked duplex with one unit above is less expensive than side-by-side. This is because the amount of roofing and foundation is reduced with one unit above the other, with the piping and electrical wiring centralized.
One-Story Duplex Side-By-Side
This type of duplex typically comes to mind: two units side-by-side, each one-story. This kind of build has more space, needing a larger roof and foundation, making it a more expensive option on average.
Two-Story Duplex Side-By-Side
While the single story is what many people think of when they hear “duplex,” this type is the most common. Each unit has two floors that mirror each other. The building has more square footage, which is more expensive due to the larger foundation, roof, decentralized plumbing, and utilities.
Project Cost Breakdown or Cost to Build a Duplex by Labor
After choosing what type of duplex you want built, your labor cost is the next factor to consider in budgeting. It’s important to note that the exact cost depends on the type of build and materials used, but we can perform a general breakdown to help with a working budget. According to Home Advisor, the cost to build a duplex by labor is the following:
- Contractor Fees: 25% of total project costs
- Foundation: 9% of the project cost
- Floor Structure: 12% of the project cost
- Walls and Exterior Finish: 6%-10% of the project cost
- Roof: 10% of the project cost
- Windows and Doors: 5% of the project cost
- Flooring: 3%-5% of the project cost
- Interior Finish: 6%-10% of the project cost
- Bathroom: 4% of the project cost
- Kitchens: 8% of the project cost
- Electrical: 10% of the project cost
- Plumbing: 12% of the project cost
- Interior Features: 3%-5% of the project cost
The amounts can give people pause, but remember that going cheaper on labor nearly never turns out well. The work is too important to cut corners for the property value and structural integrity. Also, remember these are percentages of your project; it depends on the materials used and the square footage.
Cost to Convert a Single-Family Home to a Duplex
Rather than building a duplex, some people think it’d be better to convert a single-family home into a duplex to save money. Not all homes can be converted into duplexes. But for those who can, Home Advisor reports that the average cost is between $80,000 and $100,000.
While that amount can be reassuring for those wanting to convert a home into a duplex, remember that many challenges can drive the cost up, such as:
- Building Codes and Zoning Regulations: Converting a single-family home into a duplex may require adherence to specific building codes and zoning regulations, which could involve acquiring permits and approvals from local authorities.
- Structural Modifications: Depending on the layout and design of the existing home, structural modifications may be necessary to create separate living spaces for each unit. This could involve adding additional walls and entrances or expanding the property’s footprint.
- Utility Separation: Duplexes typically require separate utility meters for each unit, which may require significant modifications to the existing plumbing, electrical, and HVAC systems to ensure they can be effectively separated.
- Parking and Access: Local regulations often require several parking spaces per unit for multifamily dwellings. Converting a single-family home into a duplex may necessitate creating additional parking spaces or ensuring adequate access for both units.
- Fire Safety Requirements: Duplex conversions must meet stringent fire safety regulations to ensure residential safety in both units. This may involve installing fire-rated walls, doors, and other safety features to meet building code requirements.
- Soundproofing: To maintain privacy and minimize disturbances between units, adequate soundproofing measures may be implemented, including insulation, soundproof barriers, and acoustic treatments.
Additional Costs
The cost to build a duplex is generally assigned to the materials, labor, and the construction itself. That gives you the duplex, but what other costs are in making the house a home?
Interior Designer
You can expect to pay between $50 to $200 an hour for an interior designer to enhance the space in your home
Attached Garage
It is common for a duplex to have a one-car garage attached for each side; for larger duplexes, two-car garages are possible. For building your own duplex, you can expect adding an attached garage to be around $35,000.
Others
In any residential construction, there are surprise costs or miscellaneous costs beyond the materials, labor, and other services used in the build:
- Appliances
- Smart home technology integrated into the duplex, such as the smart thermostat that automatically adjusts the temperature settings in your home to reduce energy costs.
- The size of the building means more materials, a larger roof, a bigger foundation, and more construction work.
- The number of rooms means more work for the interior designer, more walls, windows, doors, and amenities.
- HVAC systems or central air conditioning.
Two-Story Duplex Side-By-Side
Duplexes that have one roof, foundation, and exterior structure. You can increase your income by renting out one or both units. While you can also rent out a second, unattached house, you still have two foundations, two roofs, and two wall structures, making the cost to build significantly higher than two kitchens and two space layouts.
On average, the cost to build a duplex is 63% of the cost to build two single-family homes.
That’s only one of the reasons building a duplex is a solid investment, whether occupying one unit and renting the other or embracing a multigenerational lifestyle.
We at HiLine Homes pride ourselves on the streamlined custom duplex construction process. By helping clients navigate the steps of a build. Our Home Consultants help you make the best decisions for your duplex goals and secure financing through our Approved Lenders list.
Discover how the cost to build a duplex can fit within your budget with expert home builders like our team at HiLine Homes.
Duplex FAQs
Due to reduced construction costs and land requirements, a stacked duplex or a townhouse-style duplex with shared walls is often the cheapest to build.
The size of land needed to build a duplex varies depending on local zoning regulations and the desired layout of the duplex. Generally, a minimum lot size of around 5,000 to 6,000 square feet is typically required.
The average square footage of a duplex can be different depending on variables such as location, design, and local building codes. However, a typical duplex might range from 1,500 to 3,000 square feet.
The construction timeline for building a duplex can vary based on weather, permitting, and project complexity. It may take 6 to 12 months to build a duplex from start to finish.
Building or choosing a duplex for sale depends on budget, location, timeline, and personal preferences. Buying an existing duplex may offer immediate rental income, but building allows customization and potentially lowers long-term maintenance costs.
The down payment for building a duplex typically depends on investing factors such as the cost of construction, financing options, and lender requirements. Generally, down payments for construction loans are commonly 20% to 30% of the total project cost.
