How Much Does It Cost to Convert a Single-Family Home Into a Duplex?

Average Cost to Convert a Single-Family Home to a Duplex

Converting a Single-Family Home to a Duplex Costs

When looking at converting a single-family home into a duplex, you’ll need to hire a number of professionals with different sets of expertise. Here’s a breakdown of what you can expect to pay for your conversion project.

Cost to Convert a Single-Family Home to a Duplex by Type

In order to be considered a duplex, each unit on a property must have:

• An exterior door (in some cases, two doors)

• A minimum of one bedroom

• A full kitchen

• A full bathroom

• Separate HVAC systems

• Their own utilities and meters

With those elements, the different types of duplexes are stacked (one up, one down), one-story side-by-side and two-story side-by-side.

“Many municipalities do not allow residential builders to construct duplexes or townhomes,” says Bob Tschudi Angi Expert Review Board member and general contractor in Raleigh, NC. “For example, in North Carolina, only builders with commercial licenses can work on multi-unit homes.”

Stacked One-Up, One-Down Duplex Conversion

Stacked duplex conversions usually cost an average of $115 per square foot. You could pay as little as $95 per square foot or as much as $220 per square foot, depending on what elements need to be added to the unit.

A stacked duplex usually consists of two identical apartments, one on top of the other. For a stacked duplex conversion, you’ll likely have to add a kitchen, an exterior door with a staircase to the second level, a separate HVAC system and separate utilities. If your home has only one bathroom, you’ll have to add a bathroom to the second unit.

Wiring and pipework are usually shared in a stacked duplex, so this conversion is a little easier than a side-by-side duplex where the wiring and pipework are separate.

One-Story Side-by-Side Duplex Conversion

A one-story side-by-side duplex conversion averages $145 per square foot, with a range of $110 to $220 per square foot, depending on what’s needed.

This type of duplex has two apartments side by side, and the property usually has a larger footprint than a stacked duplex. In addition to the likelihood of adding a kitchen, you may have to add a bigger foundation and more roofing, which contributes to a higher price tag. The plumbing and wiring have to be decentralized for side-by-side duplexes, so that also plays a role in the cost.

Two-Story Side-by-Side Duplex Conversion

The average cost for a two-story side-by-side duplex conversion is $175 per square foot, with an average range of $130 to $220 per square foot.

Adding a kitchen is a large part of the cost with this type of conversion, as is separating out the entrances, plumbing, wiring and possibly expanding foundation and roofing. If both units don’t have a bathroom, you’ll need to add at least one bathroom for each unit. Two-story duplexes are usually more spacious than one-story and stacked duplexes and have a higher resale price.

Cost to Convert a Single-Family Home to a Duplex by Style

Aside from the different types of duplexes (stacked, side-by-side), duplexes come in a range of styles, some of which lend themselves to easier conversion than others.

Colonial Duplex

The cost to convert a single-family home into a Colonial duplex is around $95 to $135 per square foot. Colonial duplexes are usually stacked and, because there is already a central staircase, converting the entrances is not as labor-intensive as some other types. Some owners choose to convert Colonial single-family homes into side-by-side two-story duplexes, which requires widening the central “tower” to contain two doorways.

Craftsman Duplex

Craftsman single-family homes can be split into any of the duplex types. The cost to convert a Craftsman single-family home into a duplex usually ranges from $115 to $220 per square foot, depending on the conversion type. Side-by-side conversions tend to cost more because a new entrance needs to be added to one side of the property.

Hampton-Style Duplex

Hampton-style duplex conversions usually range from $190 to $220 per square foot. A single-family Hampton home converts into a two-story side-by-side duplex, and each side usually has a single-car garage, which adds to the cost of the conversion. Hampton homes have luxury features such as butler’s pantries, gourmet kitchens and a deep central staircase.

Mid-Century Duplex

Mid-Century single-family homes are usually converted into side-by-side duplexes. Conversion averages $200 to $230 per square foot, because mid-century homes are typically asymmetrical, which makes conversion more difficult. These homes have a contemporary look featuring clean lines.

Modern Farmhouse Duplex

Converting a single-family modern farmhouse into a duplex averages $95 to $220 per square foot, depending on the conversion style. These homes can be converted into stacked or side-by-side duplexes, and feature large front porches and optional individual garages.

Ranch-Style Duplex

A ranch-style conversion is typically a single-story side-by-side duplex conversion and runs $110 to $220 per square foot. Occasionally, ranch style-homes have two stories, but that’s a rare design feature. These homes usually have open floor plans and would need a second kitchen installation and separation of the HVAC, plumbing and wiring at a minimum.

Victorian Duplex

The most common conversion for a single-family Victorian home into a duplex is the stacked configuration and runs from $95 to $220 per square foot. These houses usually appear as single-family homes even though there are two units inside. A side-by-side conversion can be done on Victorian homes, usually into a two-story side-by-side, but it’s not a common choice.

Single-Family Home to Duplex Conversion Cost Factors

A few things can impact the cost to convert a single-family home into a duplex.

Zoning/Permitting

Before beginning your conversion, confirm that you can have the zoning on your home changed from a single to a double. Depending on your geographical location, the permitting cost for changing zoning averages $500 to $5,000.

Structural Requirements

The structural elements you have to add to your home to change from a single-family to a duplex will significantly impact the cost of the project. For example, the cost to add a kitchen averages around $65,000, which is a commonly needed feature in a conversion. Make sure you determine all the elements you’ll need to add in your conversion when putting together your budget.

Utilities

In a duplex, each unit must have separate meters for electricity, water and gas. While stacked duplexes can share their ductwork, side-by-sides usually have their own, so converting to two separate sets of ductwork will tack on costs. Meter installations usually cost $400 to $600 per meter, and ductwork usually runs $10 to $20 per linear foot.

Lender/Home Value

Converting your single-family home to a duplex will have an impact on the value of your home. If you still have a mortgage, your lender will see an impact as well. If your home value declines because of the conversion, you’re less likely to get approved for a loan in the future, whereas if your home value increases, your future approval odds may go up.

Taxes

If you convert your single-family home to a duplex, your property taxes will rise. However, you’ll be able to offset some of this expense because you can deduct utility, property taxes, maintenance costs, mortgage interest and insurance on any rental properties. The tax treatment of the property depends on the location, so do your research before beginning your project so you know exactly how much your tax liability is going to change.

DIY vs. Hiring a Pro to Convert Single-Family Home to a Duplex

The amount of work necessary for converting a single-family home to a duplex makes it an impractical DIY project. You’ll need several different pros to complete the project, including a local architect, a local electrician, a local general contractor, a local plumber and others depending on the project scope. However, you may be able to save on things like interior finishing, painting, laying flooring and other touches by doing those yourself.

FAQs

Is a duplex a multi-family dwelling?

Yes, a duplex is considered a multi-family dwelling as it contains two individual units for two families.

What’s the difference between a duplex and an apartment?

The only difference is that the term duplex refers to a dwelling that has only two units, where an apartment is usually one unit in a larger building with more than two units. In a duplex, you’ll only have one neighbor to share floors/walls/ceilings with, but in an apartment, you could have people on both sides of you or above and below you.

How many bedrooms are in a duplex?

A duplex contains at least two bedrooms (one in each unit) and usually has two or four.

Is a single-family to duplex conversion worth it?

In many cases, you’ll be able to add an additional income stream from renting the new unit. Since the home will now be looked at as an investment property, your property value is likely to increase. But converting a single-family home into a duplex requires a lot of time and upfront investment, so deciding whether it’s worth it to convert is a personal decision.