How Much Does It Cost to Convert a House to a Duplex in 2025?
Converting a house to a duplex costs an average of $150,000
Most homeowners spend an average of $150,000 to convert a house to a duplex.
Major cost factors include the floor plan, selected components, material prices, and labor costs.
Most duplex conversions require the services of a structural engineer, a contractor, a plumber, and an electrician.
Not all zoning districts permit duplex conversions, so obtain the necessary permits before construction begins.
This article was updated using automation technology and thoroughly reviewed for accuracy by HomeAdvisor Editor Ryan Noonan.
The cost to convert a house to a duplex can vary widely, but the average project runs $150,000, with most homeowners spending between $90,000 and $200,000. Create a detailed budget that encompasses design changes, structural work, and professional labor, ensuring the finished duplex meets your goals.
House-to-Duplex Conversion Cost Factors
The size and layout of your home, the components you choose to include, and the raw materials you use are all key cost factors when estimating your house-to-duplex conversion project.
Home Layout
Ideally, the house already offers two similar-sized living areas. In that scenario, the conversion remains straightforward—add a dividing wall, reroute the HVAC and plumbing, and proceed without major new construction.
If one side is much smaller, expect to add square footage so both units feel functional and code-compliant. In this case, the average cost to build new components for a duplex ranges from $ 100 to $250 per square foot.
Components
Components drive cost. Prices swing from simply installing extra cabinets to building an entirely new bathroom.
Materials
When adding walls, replacing floors, or installing new finishes, factor material costs into your overall budget from the start.
| Material | Average Cost per Sq. Ft. |
|---|---|
| Drywall | $1.50–$3.50 |
| Flooring | $4.00–$15.00 |
| Interior trim | $4.00–$10.00 |
| Insulation | $1.00–$4.50 |
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 separate roofs. Both styles have separate exterior exits.
Side-by-side units cost more because they call for extensive plumbing changes. Multi-story conversions can edge higher if you need exterior stairs and a second entrance.
Finishes
After the structural work is complete, add the finishing touches. New walls and trim almost always need fresh paint—budget $25 to $50 per gallon for materials and $2 to $6 per square foot if you hire professional painters.
Other Duplex Conversion Cost Factors
Labor
Converting a house to a duplex requires a team of pros. If you plan to add or remove walls, consider consulting a structural engineer to ensure the project remains safe and code-compliant.
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.
| Professional | Average Cost Per Hour |
|---|---|
| Architect | $125–$250 |
| Structural engineer | $100–$250 |
| General contractor | $50–$150 |
| Plumber | $45–$200 |
| Electrician | $50–$100 |
Permits
Many zoning districts limit or prohibit duplexes. Confirm local rules with the permitting office before work begins, and ask your contractor to obtain the necessary 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 $800 and may be necessary for obtaining building permits.
Does Converting a House to a Duplex Increase Home Value?
A well-executed duplex conversion can often significantly boost property value and generate steady rental income. Living in one unit and renting the other can offset mortgage payments and help recoup the conversion cost.
Converting a house into a duplex may also increase the property value, depending on the local market. 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:
Confirm zoning early: Check local rules first; many districts restrict duplexes and always require permits.
Compare material prices: Get quotes on drywall, insulation, cabinets, and countertops, and ask your contractor about seasonal or bulk discounts.
Handle simple DIY tasks: Paint new walls or install trim yourself to trim labor costs, but leave plumbing, electrical, and HVAC to licensed pros.
Get several bids: Request detailed quotes from at least three home remodelers in your area before signing a contract.
DIY vs. Hiring a Pro for a Duplex Conversion
Tackling a house-to-duplex conversion yourself might seem like a way to cut labor costs, but it comes with big challenges. While experienced DIYers can handle simple tasks like painting or non-structural demolition, most conversions demand specialized skills in plumbing, electrical work, and framing.
Even if you go the DIY route, you’ll still need to cover permit fees, material costs, and potentially expensive tool rentals—plus the risk of costly mistakes if anything falls out of code. Licensed professionals are required for major construction and system upgrades, which is why full DIY conversions are uncommon and best reserved for those with solid building experience.
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.
