How Much Does an In-Law Suite Cost?

Average Cost to Build an In-Law Suite Addition

In-Law Suite Addition Costs by Type

If you’re planning to have family members move into your home, you can convert existing rooms, including the basement or attic, into a functional suite. To add a rental property, you might consider turning your garage into an ADU or building a new structure.

Converting a Finished Room

You can turn an existing, finished room in your home into an in-law suite for about $10,300 to $11,250. This includes the cost to add a bathroom or thecost to build a kitchen, both needed to convert an existing room into a fully functional in-law suite. Each of these additions costs about $5,000 minimum. Installing new walls costs $1,800 per wall on average.

Extending a Room

The cost to bump out a room for an in-law suite is $20,600 to $54,800. More than simply converting a room, an extension also involves expanding on the foundation at $75 per yard, excavating around the home’s perimeter at $2,600 on average, installing insulation and wiring, and matching exterior paint or siding. Extending a second-floor room costs even more than a first-floor room.

Converting a Garage, Basement, or Attic

If you aren’t ready to dig up precious space in the backyard to build an ADU, consider converting existing unused parts of your home into an in-law suite. Keep in mind that each type of space will need to be outfitted with drywall, insulation, flooring, HVAC, a water heater, plumbing, gas line or 220 outlet, private entrance, bathroom, and kitchenette to function as a separate dwelling.

• Garage: With a foundation already in place, you can convert a garage to an in-law suite for $20,000–$60,000.

• Basement: By tapping into the main home’s plumbing, the cost of a basement remodel for an in-law suite can be as little as $10,000–$30,000.

• Attic: An attic conversion is more expensive at $40,000–$100,000 due to the need for reinforced floor joists and a safe stairway.

Building an ADU

The average cost to build a guest house or an ADU on your property is about $82,500, but typically ranges from $40,000 to $125,000 or more depending on your design preferences and needs. In some regions, you could pay up to $400,000 for an average single-story detached ADU.

In-Law Suite Addition Costs by Size

You can expect to spend about $100 to $200 per square foot for the cost of an in-law suite, including materials and labor.

• 400 square feet: A small, 400-square-foot suite costs $40,000–$80,000

• 500 square feet: A 500-square-foot in-law suite costs $50,000–$100,000

• 600 square feet: A 600-square-foot addition costs $60,000–$120,000

• 750 square feet: In many municipalities, this is the maximum size allowed for an ADU. A 750-square-foot suite would cost $75,000 to $150,000.

In-Law Suite Addition Costs for Labor

To build an in-law suite, you’ll need to hire several professionals, including architects, electricians, HVAC/mechanical technicians, and plumbers.

Architect

Hiring local architectural services will cost about 10% to 20% of the project’s total cost. For example, for a $100,000 ADU, you’d spend an additional $10,000 to $20,000 for an architect. Hiring an architect will help you plan an efficient, functional in-law suite. If you’re moving in older family members with limited mobility, discussing universal, accessible design with the architects is important. 

Electrician

A new in-law suite will need electrical work, which costs an average of $50 to $100 an hour. Work includes essential changes to your home’s current electrical system to bear the load of multiple families living under one roof. For safety, the unit needs lighting leading to an outdoor exit, as well as smoke alarms and carbon monoxide detectors connected to the main home.

Plumber

Both the bathroom and kitchen of the suite will require new plumbing, and the bathroom must connect to the sewage system. Plumbers charge about $200 an hour for these intensive jobs.

• Water main installation: $600–$2,500

• Plumbing pipes: $300–$2,000

• Sewer main installation: $1,500–$5,000

HVAC

Depending on the size of the space, HVAC (heating, ventilation, and air conditioning) can be a relatively inexpensive extension of your existing systems, or require the installation of a new system. A new HVAC system costs around $7,500 on average.

“Many of our clients choose what is called a ‘mini-split’ system,” says Bob Tschudi, Expert Review Board member and Raleigh, NC-based general contractor. “These systems are great at heating and cooling smaller spaces and cost a fraction of a traditional HVAC system with ducts, vents, and air returns.”

General Contractors

You can hire local addition and remodeling contractors for many parts of the process, such as building the structure, painting the interior and exterior, laying floors, and installing windows. You’ll typically have a general contractor oversee the entire project, which costs 10% to 20% of the total. Additional workers who build, install, and paint cost about $100 to $300 per laborer, per day.

In-Law Suite Addition Material Prices

An in-law suite is similar to an apartment or tiny home, meaning you need many materials to build this structure inside and out. You’ll need everything from wall support beams to new floors to bathroom fixtures and kitchen stoves. The material costs to build an addition will vary depending on your design choices.

• Support beams and roof trusses: For new construction, whether an extension of your home or a new structure on the property, you’ll need to build out the supportive frame. This will cost $15 to $30 per square foot.

• Drywall and insulation: Adding drywall will cost $400–$600 for every 100 square feet, and insulation will cost $0.30–$1 per square foot.

• Foundation materials: Building a new structure on your property requires a foundation or a load-bearing base level. This will cost $400–$700 for 100 square feet.

• Bathroom plumbing: The in-law suite needs its own bathroom, whether built into an existing room or added to a new structure on your property. Plumbing materials, like pipes, will cost $1,500–$4,000 for 100 square feet.

• Plumbing fixtures: New plumbing fixtures, like sink faucets, sinks, showerheads, bathtubs, and toilets, will vary widely in cost depending on your preferences. Expect to spend around $400 to $2,000 for each plumbing fixture.

• Electric meter: You’ll need to install a separate electric meter for a detached property, especially if the person living there will be paying their own utilities. A new meter will cost $2,000–$5,000.

• Water heater: A water heater is another necessity for a detached suite, and it will cost anywhere from $600–$3,000.

• Paint: Adding new paint to an in-law suite will range from $5,000 to paint the interior and an additional $8,000 for the exterior.

• Siding: Siding for an ADU costs about $10,000. The average is around $12 per sq. ft.

• Windows: Expect to spend anywhere from $100 to $1,500 per window.

• Doors: New doors for the interior and exterior will range from $500 to $5,000 each.

• Floors: Adding new floors will cost around $5 to $20 per square foot, with options like hardwood or marble costing more, while laminate or vinyl will be less expensive.

Benefits of Adding an In-Law Suite

An in-law suite is a flexible addition to your property that can offer many benefits. On the one hand, you can bring multiple generations of family under one roof, giving elder parents accessibility and independence. On the other hand, you can generate income with a rental property and increase your home’s value.

DIY In-Law Suite Addition vs. Hiring a Pro

There’s no way around it: you need to hire multiple professionals to build an in-law suite addition. This process requires permitting, excavations, construction, electrical work, HVAC, and plumbing, so you need to work with several experts to do the job. Start by finding the right local general contractor. They’ll help you manage the project and assemble the team you need.

If you convert an existing room or basement into an in-law suite, you might save several thousands of dollars on labor costs by taking on the project as a DIY. But even converting a room has risks—especially if you need to install a new bathroom for the resident. It’s crucial to invest in skilled professionals to add an in-law suite to your home or property.

Cost to Build an In-Law Suite Addition Yourself

Building an addition is a huge undertaking that requires construction, plumbing, HVAC, and electrical know-how. You’ll need to consult several contractors to complete this project; we do not recommend that you DIY this project. Even an experienced DIYer should leave this huge and dangerous job to professionals.

However, contractor labor costs make up about 30% to 50% of your total budget for a home addition project. You can take on certain tasks yourself (depending on your skill level) to cut some costs. For example, handy homeowners can lay flooring as a DIY for $0.50 to $20 per square foot. You can also do the interior painting for just $200 to $300.

If you’re interested in saving money on your project, be sure to do research in your area. Compare similar properties near you and aim to spend less on your build than on the projected increase in your home’s value, which can reach up to 30%.