How Much Does It Cost To Build A Duplex

Families with large houses tend to turn their homes into a duplex unit, which has two but completely separate accommodations under a single roof. While most Americans want to live independently, others still wish to live next to their parents, their favorite married sibling, or their best friend. For whatever reason, it will be wise to know the costs of building a duplex.

Estimated Costs to Build a Duplex


As a basis, real estate experts estimate the cost of house construction to be around $150 to $200 per sq. ft. This means that you would likely spend between $225,000 and $300,000 for a house with 1,500 sq. ft. area.

The cost to build a duplex depends on major factors like the size of the unit, the location, and the current status of the housing market. However, the national average is around $138,500 for a standard dwelling with an area of 900 square feet or a 30×60 feet footprint. This translates to around $154 per square feet using mid-range quality materials.

Additionally, this estimate includes the installation of cost-effective doors and windows, the formation of an efficient foundation, a fullyfinished basement, a turnkey finishing, and all the necessary appliances.

Apparently, the said duplex building costs do not cover the price of acquiring the building or site where the building is going to be built. You still need to pay for the lot, especially when the duplex is not going to be built from a pre-existing house.

Duplex Construction Cost

Keep in mind that you can never construct a duplex unit by yourself just because you think you can and you feel the need to save on cost. Even if you plan to supervise the project yourself, you will have to hire the services of an architect and a team of laborers.

On the other hand, a contractor or a cooperative developer can come in handy to make sure that the construction is done correctly and at a much faster pace. It may be more costly from your perspective but definitely a safer and more cost-effective in the long run. This is because reputable contractors are duly insured so any damages or any accidents that may arise during the construction are covered.

If you decided to hire construction personnel individually, below are some of their prevailing hourly rates to give you an idea. Please note that these vary depending on location and expertise.

  • Labor/Helpers – $15 to $22
  • Carpenters – $25 to $50
  • Excavators and masons $30 to $70
  • Electricians $45 to $120
  • Plumbers – $85 to $160
  • Painters – $25 to $50

Cost of a Two-Story Building

Apart from those above costs, you should remember that the cost to construct the second floor of your duplex house will not go lower than the price per square foot of the first-floor construction. Typically, the cost will be 20% higher, assuming the materials are of the same quality. The additional costs are mostly attributed to the additional foundation needed to carry the extra weight of the second floor.

Given the example above, expect the cost to be around, at least, $166,000 for a 900 sq. ft. for the second floor unit of your duplex home. Please do note that the cost of construction is almost always directly proportional to the cost of real estate in a particular county, city, or state.

For example, for the same square footage, it can cost around $270,000 to $360,000 in San Diego, California. On the other hand, the cost can range from $450,000 to $585,000 in Seattle, Washington.

Still, these figures do not include the price of land acquisition and the costs of adding improvements on the lot such as putting up gardens, playing areas, and a parking lot or demolition jobs.

The Architect and the Contractor

In building a duplex, the usual designs come in four-square and rectangular shapes. In most cases, developers would need the expertise of a professional architect and a contractor, which means additional costs for the completion of the project. The architect fee takes around 10% to 17% of the overall price of building a duplex.

The architect’s many responsibilities include the following:

  • determines the scope of the duplex construction
  • establishes the initial budget
  • comes up with a schematic design and create draft floor plans
  • consults with engineers and planning agencies to complete the requirements
  • completes the drawings that are incorporated with the necessary materials and finishes
  • obtains the needed permits and completes the documents for construction
  • administers the construction
  • works hand-in-hand with the contractor

Just like the architect, a contractor also has a handful of tasks to carry out until the project is completed. These include:

  • manages the project every day
  • provides the required materials and services to get the work done
  • hires a team of subcontractors when the need arises
  • gives suggestions to the developer to achieve the goals
  • obtains all the working permits and the documents for the utility installation
  • checks the services and supplies

Factors Affecting The Cost of Building A Duplex

Size of the project – the cost is always dependent on the size of the construction project. However, the cost per square foot sometimes decreases as the project size increases. That’s if all other things remain constant.

Number of rooms – adding rooms naturally adds up to the cost as you will be needing more materials for the additional partition or walls, windows, doors, and accessories.

Type of materials – your choice of materials would also spell some difference on your overall costs. You may opt to use wood, steel, or concrete or a combination of them all. Oftentimes, opting for the higher quality materials can be more practical in the long run as you can avoid having to replace or repair them every so often and to hire a handyman or contractor to do the job.

Style and design of the project – your choice of whether to have a modern design, minimalist, or just about anything you prefer will definitely impact the type of materials you need to purchase and how much architectural load you will be assigning to your contractor or architect of choice.

Location – the place where you reside will always have a huge impact on the overall cost of construction. This simply because the location impacts the price of commodities such as the price of materials, labor cost, as well as professional fees. Some areas may also require costly building or construction permits before you can commence the construction.

Whether DIY or hire a contractor – when you are an engineer yourself or have sufficient experience being a contractor, doing the project by DIY route can be a practical choice to save on cost. Otherwise, doing so would be a major risk. Hiring a contractor would still be the safest choice. In case of errors that lead to major damages, as mentioned, insurance companies can cover these costs as most contractors are duly insured.

Whether there is an existing structure or not – another major factor in the overall cost is whether there is an existing structure or you will be building from scratch. Naturally, the existing structure will have to be demolished first if it will not be part of the new project.

Time of Year – like seasonal commodities, house construction, in general, tend to be more costly during high season. If you are building your duplex strictly on a budget and you reside in an area where fluctuation in the weather is commonplace, consider commencing the project during the slow season.

1 thought on “How Much Does It Cost To Build A Duplex”

Leave a Comment