How Much Does It Cost to Build an In-Law Suite? [2024 Data]
Normal range: $25,000 - $265,000
The average cost to build an in-law suite ranges from $25,000 to $265,000, with a national average of $82,750. Expect to pay more for detached dwellings and room additions.
Do you want to add an extra living space to your property for visiting family or potential rental income? The average cost to build an in-law suite has a wide range of $25,000 to $265,000 with an overall national average of $82,750.
Costs vary greatly between room conversions and new construction as well as between attached and detached units. Size and features included also impact the cost of labor, materials, permits, and more.
- Average
- $82,750
- Low end
- $7,500
- high end
- $600,000
Cost by Type of Addition
There are many types of in-law suite additions. The type you choose will depend on whether you want to adapt an existing part of your home, extend your home, or create an entirely separate structure. Your budget and local building codes will also help guide your decision. Whatever space you design will likely require most of the following:
Drywall and insulation
Flooring
Plumbing and a bathroom
Water heater
HVAC
Gas line
Private entrance
Kitchen or kitchenette
We break down different in-law suite types and costs below.
| Addition Type | Average Cost Range |
|---|---|
| Converting a finished room | $10,150–$65,625 |
| Extending a room | $26,600–$54,800 |
| Adding a room | $40,000–$200,000 |
| Converting a garage | $20,000–$60,000 |
| Converting a basement | $10,000–$30,000 |
| Converting an attic | $25,000–$65,000 |
Converting a Finished Room
An existing, finished room in your home can be converted to an in-law suite for $10,150 to $65,625.
Extending a Room
The cost to bump out an existing room is $26,600 to $54,800. This requires excavation around and expansion on your home's foundation along with new insulation, wiring, and matching exterior paint or siding. Expect to pay more if you want to extend a second-floor room.
Adding a Room
A full room addition costs $100 to $200 per square foot, or roughly $40,000 to $200,000 on average. The high cost is because the new construction often requires a full team of contractors. Many homeowners opt to add a room above a garage.
Converting a Garage, Basement, or Attic
Converting a garage or basement is often ideal for an in-law suite since it already has framing and foundation. Expect to spend $20,000 to $60,000 to convert a garage and $10,000 to $30,000 to finish a basement. An attic is more complex due to the need for reinforced floor joists and a safe stairway. Expect to spend $25,000 to $65,000 on finishing an attic.
Material Prices for an In-Law Suite Addition
Building an in-law suite is a complex construction project that involves many different materials. Below are some of the costs you can expect.
Framing: $15 to $32.50 per square foot
Foundation: $4 to $16 per square foot
Drywall: $4 to $6 per square foot
Insulation: $0.30 to $1 per square foot
Plumbing: $15 to $40 per square foot
Plumbing fixtures: $400 to $2,000
Wiring: $2 to $4 per square foot
Windows: $100 to $1,500 each
Doors: $500 to $5,000 each
Roofing: $120 to $400 per square
Flooring: $3.50 to $21 per square foot
Siding: $12 per square foot
Size of In-Law Suite Addition
As with many projects, the larger your in-law suite addition, the more you can expect to pay. A small extension will cost much less than a separate ADU. On average, expect to spend anywhere from $100 to $200 per square foot on materials and labor combined.
| Addition Size (Square Feet) | Average Cost |
|---|---|
| 100 | $10,000–$20,000 |
| 200 | $20,000–$40,000 |
| 300 | $30,000–$60,000 |
| 400 | $40,000–$80,000 |
| 500 | $50,000–$100,000 |
| 600 | $60,000–$120,000 |
| 750 | $75,000–$150,000 |
| 1,000 | $100,000–$200,000 |
| 2,000 | $200,000–$400,000 |
General Contractor Cost
You’ll want to hire a local remodeling contractor that specializes in additions. The benefit of a general contractor for a project of this scale is they can build out the structure, paint, lay floors, install windows, and more. A contractor costs about 10% to 20% of the total project price. This amounts to about $300 to $500 per day, plus $150 to $250 per day for each additional laborer.
Electrician Costs
Any new living space will require electrical work. Most electricians charge between $50 and $100 per hour. Some of the necessary electrical tasks include:
Electrical panel upgrades: $1,600
Rewiring: $6,000
Adding light fixtures: $500 each
Installing outlets: $300 each
Plumber Costs
To qualify as a separate living space, your in-law suite will need a bathroom and kitchen. Both of these spaces will require new plumbing, and most plumbers charge $150 to $275 per hour. Plumbing tasks may include:
Rough-in plumbing: $6,500
Installing a sink: $450
Water heater installation: $1,400
Sewer main installation: $3,500
Additional Cost Factors
Materials and labor aren’t the only costs for an in-law suite. Keep the following in mind as you prepare for your project.
Permits
Whether you're remodeling or building a new structure, you'll need many permits for your in-law suite. Either the homeowner or the contractor can pull the required permits, but you should contact your city government for more information.
Building permit costs vary by type—here’s a look at common permit prices.
| Permit Type | Average Cost |
|---|---|
| New construction | $150–$2,000 |
| Roofing installation | $250–$500 |
| Garage or basement conversion | $1,200–$2,000 |
| Electrical work | $10–$500 |
| Plumbing work | $50–$500 |
| Window installation | $50 per window |
| HVAC installation | $250–$400 |
Egress Window
For your in-law suite to be considered an independent living space, it needs a safe exterior exit and entrance for guests, residents, and emergency personnel. In a basement, this often takes the form of an egress window, which must fit specific measurements.
Utility Meters
If you plan to rent your in-law suite and want your tenants to pay separate utilities, you’ll need an electrical meter. Adding a meter costs $2,000 to $5,000 depending on local regulations.
HVAC Installation
The cost of HVAC installation ranges from $5,000 to $12,500 and depends on the extent of your project. Extending your current HVAC system into an addition will cost significantly less than installing an entirely new system in an ADU.
Architect Designs
Whether you need an architect for an addition is up to you. They can help plan your in-law suite to ensure you get the most out of your investment. They're especially important if you're designing an accessible space for an older family member with mobility issues. Expect to pay an additional 10% to 20% of the total project price for the cost of hiring an architect.
DIY In-Law Suite Construction vs. Hiring a Pro
We don’t recommend taking on a building addition like an in-law suite as a DIY project. Between permits, excavation, construction, electrical work, HVAC installation, and plumbing, many types of expertise are required, and lots of dangerous work is involved.
Instead, hire a general contractor to help you assemble a team of professionals and consider saving on small, manageable tasks. Laying vinyl flooring or painting interior walls are good examples of low-risk DIY tasks that homeowners can complete.
In-Law Suite Renovation vs. Remodel vs. Expansion
You may hear the terms renovation, remodel, and expansion as you plan your in-law suite and talk to pros. Learn the difference between each term and what they involve.
Renovating an In-Law Suite
If you already have a functional living space with working plumbing and kitchen appliances, you may just need a renovation. Repairing or replacing appliances, refinishing floors and cabinetry, and replacing plumbing fixtures are all ways to renovate a space.
Remodeling an In-Law Suite
Another way to approach an existing space is a full remodel. You may need to change the layout and placement of appliances to make a space functional as an independent in-law suite. This can involve adding windows and doors, removing walls, rerouting plumbing, and upgrading your electrical system. By the end of a remodel, your in-law suite will look completely new.
Expanding an In-Law Suite
If you want to increase the square footage of a space to provide more room for guests or residents, you'll likely need to bump out walls and lay additional foundation. This also involves extra exterior coverings and roofing, all of which come with higher costs.
| In-Law Suite Renovation | In-Law Suite Remodel | In-Law Suite Expansion |
|---|---|---|
| Refinish and refurbish the space | Layout may change, including placement of appliances | Bump out an existing room to increase square footage |
| Layout remains the same, with a focus on repairs and replacements | May involve new doors, windows, plumbing, and electrical connections | Typically involves new foundation, exterior siding, and roofing |
| Costs are relatively low to moderate | Costs are moderate to high | Costs are moderate to high |
How You Can Save Money While Building an In-Law Suite
Aside from handling smaller tasks on your own, there are some significant ways to save on the overall cost of an in-law suite.
Opt for a modular or prefabricated home addition
Convert an existing space rather than building from scratch
Build upon your home's existing foundation when possible
Keep your timeline flexible in case of changing material costs
Compare quotes from multiple contractors
Opt for an attached addition over a detached ADU
Opt for a kitchenette over a full kitchen
Connect the new plumbing to your home's existing plumbing
Does Building an In-Law Suite Increase Home Value?
"There is some demand in the market for ADU's, specifically in-law suites. Most of this is driven by new homebuyers looking for ways to help pay their mortgage by renting space without having to qualify for an additional loan to purchase a separate investment property. This has increased as mortgage rates have continued to increase and homebuyers look for ways to save."
— Maureen McDermut, Realtor at Sotheby's International-Montecito
An in-law suite or guest house can add value to your home in several ways. Any time you add square footage, you'll add value. Overall, expect to see up to a 30% increase in your property value when you invest in an in-law suite.
An in-law suite can also double as a rental property, giving you and potential buyers the opportunity to earn an additional $15,000 to $30,000 of annual income. If you plan to operate a rental property, you should check with your local municipality and homeowner's association beforehand to ensure you meet all the requirements.
Frequently Asked Questions
The benefits of adding an in-law suite include the opportunity to bring multiple generations of your family under one roof. An in-law suite can provide elderly parents and family members with independence and accessibility while avoiding the costs associated with assisted living. Alternatively, you can generate rental income and increase the overall value of your home.
The floor plan for a mother-in-law suite can vary, but should, at minimum, include a sleeping area and full bathroom. Most also include a small kitchen or kitchenette and a living area. Larger suites may also have space for an office or laundry room, which can add utility and increase independence for guests and residents.
How long it takes to build an in-law suite will vary by type. The time it takes to build an addition will typically be less than for completely new construction. Expect to spend about two months if you convert a basement, attic, or other existing room in your home. New structures can take up to five months, plus up to two months to receive the required permits.