How Much Does It Cost to Convert a House to a Duplex in 2025?

Average Cost to Convert a House to a Duplex

House-to-Duplex Conversion Cost Factors

The size and layout of your home, the components you choose to include, and your raw materials are all key cost factors when estimating your house-to-duplex conversion project.

Home Layout

When you’re considering whether to convert your home to a duplex, it’s best if your home is laid out in a way that has two fairly equal-sized living spaces. In this case, modifications will be fairly straightforward—you may need to build a dividing wall and reroute HVAC and plumbing, but you won’t generally need to undertake additional building. 

However, if your layout means that one side is significantly smaller, you may need to build an addition to create a comfortable duplex. In this case, the average cost to build new components for a duplex ranges from $95 to $220 per square foot.

Components

A key factor in your duplex conversion costs is the components you choose to include. This can be as simple as installing a few cabinets or as complex as adding a new bathroom. 

Materials

For larger modifications like adding walls or redoing floors, it’s important to factor the cost of materials into your total cost calculations.

Design Complexity

There are two primary designs for duplexes: multi-story and side-by-side. Multi-story duplexes have one unit stacked on top of the other, while side-by-side units have their own separate roofs. Both styles typically have separate exterior exits.

Side-by-side units are often more costly since they typically require bigger changes to plumbing. However, a multi-story unit may cost more if you have to install exterior stairs to add a new entrance.

Finishes

Once you’ve completed major changes and installations, you’ll need to put the finishing touches on your space. For example, new walls and trim typically require a coat of paint, with paint costs averaging $25 to $50 per gallon. If you’d like to hire professional painters for the job, budget between $2 to $6 per square foot in labor costs.

Other Duplex Conversion Cost Factors

In addition to your existing home layout, it’s important to budget for labor costs, permits, and home inspections before you begin construction.

Labor

Converting a duplex often requires hiring multiple professionals. Particularly if you’re adding or removing walls, you’ll want to consult with a structural pro to ensure your home remains structurally safe and sound. 

Many home professionals charge by the hour, although some may prefer to offer a per-project quote. Shop around and obtain multiple quotes to find the right fit for your duplex conversion.

Permits

Not all zoning laws allow you to convert a single-family home into a duplex, so it's important to check with your local permitting office before you begin your project. Your contractor may also be able to help you obtain the required building permits.

Inspection

Before you begin construction, it’s a good idea to conduct a home inspection to ensure your structure is sound and suitable for conversion. On average, a home inspection costs between $300 and $450 and may be necessary for obtaining building permits.

Additional Upgrades

In addition to rerouting electricity and plumbing, you may also need to reroute HVAC to ensure both duplex units receive good heating and cooling capacity. Adding or modifying HVAC typically costs $25 to $60 per square foot.

Converting a home to a duplex also often requires building a second kitchen. You'll need to budget for kitchen appliances as well as basics like countertops and cabinets. These can run anywhere from $2,500 to $6,800 per kitchen.

Landscaping Repair

Creating or modifying a duplex may require some exterior work, especially if you’re adding an outdoor entrance. Once you’re done, you may want to hire a landscaping pro to repair the outdoor space. Landscaping costs an average of $50 to $100 per hour, although some landscapers may prefer to charge by the task—for example, tree planting, shrubbery installation, or landscape grading.

Does Converting a House to a Duplex Increase Home Value?

In many cases, converting a single-family home to a duplex can be a good way to increase home value. The primary benefit of a duplex is that it allows homeowners to live in one unit and rent out the other, providing a steady stream of income. This can be used to pay mortgage payments and help pay off the cost of the conversion.

Converting a house to a duplex may also increase the property value, depending on the market in your area. It’s a good idea to browse and compare the market prices of single-family homes and duplexes in your state to assess whether there’s a strong demand and how much the conversion might increase your home’s value.

Budgeting for Converting a House to a Duplex

Converting a home to a duplex requires the skills of multiple professionals, including architects, structural engineers, and contractors. However, there are several steps you can take to ensure your project stays on budget:

• Research your zoning laws: Before you begin hiring contractors, research your local zoning laws to make sure you can legally convert your home to a duplex. Not all areas allow duplex conversion; those that do still typically require building permits before construction can begin.

• Shop around: You’ll likely need quite a few materials for your conversion, including drywall, insulation, and things like countertops and cabinets. Shop for seasonal deals and talk to your contractor to see if they can access any special discounts.

• Tackle small tasks yourself: While major changes like rerouting plumbing, electrical, and HVAC require a pro, there are plenty of details you can tackle yourself if you’re comfortable with DIY. Installing interior trim and painting new walls yourself can save you money on labor costs.

• Contact multiple pros: Talk to several home remodelers in your area to compare quotes and find the best fit for your project.

How HomeAdvisor Gets Its Cost Data

No place is more important than your home, which is why HomeAdvisor connects homeowners with local pros to transform their houses into homes they love. To help homeowners prepare for their next project, HomeAdvisor provides readers with accurate cost data and follows strict editorial guidelines. After a project is complete, we survey real customers about the costs to develop the pricing data you see, so you can make the best decisions for you and your home. We pair this data with research from reputable sources, including the U.S. Bureau of Labor Statistics, academic journals, market studies, and interviews with industry experts—all to ensure our prices reflect real-world projects.