Mother-in-Law Suite: Should You Buy or Build?

• Nearly 1 in 5 Americans now live in multigenerational homes, doubling since 1980.

• Homes with accessory dwelling units can increase in value by 20–30%.

• ADUs can lead to tax implications like reassessments and income taxation.

• Building an ADU takes significantly longer than buying a home with one already included.

• Listings may not use the term “mother-in-law suite”—look for “casita,” “guest unit,” or “ADU.”

What Is a Mother-in-Law Suite?

A mother-in-law suite, also called an accessory dwelling unit (ADU), is a self-contained living space on the same property as a main house. These units work as independent homes but are still part of the same lot. They come in many forms. Some are finished basements, converted garages, or separate backyard cottages. Others are additions built right onto the main home. What makes an ADU or in-law suite special is that it usually has its own entrance, bathroom, kitchen (or kitchenette), bedroom, and living area. These spaces give occupants independence, whether they are older family members, adult children, or renters.

And don’t be surprised if listings don’t directly say “mother-in-law suite” or “ADU.” Instead, look for terms like “guest house,” “second unit,” “casita,” “dual living,” or “multigenerational housing.”

Why More People Want Homes With In-Law Suites

More people want homes with in-law suites or ADUs. This isn’t just a passing trend. It shows big changes in how people live and spend money. Home prices are going up, more people are getting older, and many want living spaces that can change with their needs. These things are making buyers look for homes with secondary units. Multigenerational living, which means different family generations share one property, is a big part of this trend.

According to Pew Research, nearly 1 in 5 Americans now live in multigenerational homes. This number has doubled since 1980.

Also, other trends causing this increase include:

• Sharing costs for housing, utilities, and property taxes.

• Having on-site care for older parents.

• ‍ Giving adult children a place to live after college as they get on their feet financially.

• Making independent rental units to earn extra money.

The good thing about an ADU is that it can change as your life does. It can meet family needs now, and then earn rental money later.

Buying a Home With an In-Law Suite: Good Points and Bad Points

Buying a property that already has a mother-in-law suite can have many benefits. But it can also come with some challenges. Here is a list to help you decide.

Good Points

• Ready to move in: You skip the time and trouble of design and building. This is great if you need the space right away.

• Better mortgage: Lenders might count the ADU’s value in the total property appraisal. This makes it easier to get a loan.

• Quick rental income: You can start earning money right away if the unit follows local rental laws.

• Easy for multigenerational living: This is great for families who want to be close but also have their own space.

Bad Points

• Few homes available: Not all areas have many homes with legal, working in-law suites.

• Permit problems: Older or do-it-yourself units might have been built without permits or break current zoning rules.

• Higher price: Homes with legal ADUs can cost more than similar homes without one.

• Possible repair costs: Older units might need updates to work well, be safe, or feel comfortable.

And deciding to buy a home with a mother-in-law suite often means you have to balance cost, timing, and how flexible you need the space to be.

How to Look for Homes With In-Law Suites or ADUs

Finding the right home with an ADU can be hard. Real estate websites don’t always have easy filters for them. Here are simple ways to make your search easier:

Use Good Search Words

Look for terms like:

• “Guest house”

• “Casita”

• “In-law apartment”

• “Multigenerational living”

• “Second kitchen” or “separate entrance”

Use Website Filters

Some real estate websites have advanced search filters. These let you look for homes with:

• Multiple units

• Finished basements

• Separate entrances

Check Online Zoning and Permit Records

Look at local government GIS (Geographic Information System) databases or permit search tools. These often show:

• How the property is zoned

• If additions or changes are legal

• If inspections were done and approved

Work With Agents Who Know Their Stuff

It’s key to have a real estate agent who knows a lot. Find an agent who:

• Knows how to spot units not called “ADU”

• Can explain zoning rules and legal status

• Might know about properties not yet listed or off-market

What You Should Know About Local ADU and Zoning Laws

When you buy or build a mother-in-law suite, local laws are very important. They control what you can and cannot do with the unit.

Common Rules:

• Minimum Lot Size: Some places only let you build ADUs on lots bigger than a certain size.

• Size Limits: The total size allowed might be capped. This is usually between 500–1,200 sq. ft.

• Distance from Property Lines: ADUs must be a certain distance from property lines.

• Parking Rules: You might need to add more off-street parking spots.

• Owner-Occupancy Rules: Some areas say that either the main house or the ADU must be lived in by the owner.

Before you make an offer or start building:

• Ask for the property’s full permit history.

• Check that final inspections and permits were approved.

• Get a zoning certificate that confirms the unit’s legal use.

And mistakes here can slow down your financing, make insurance cost more, or stop you from renting the unit.

Should You Build Your Own Mother-in-Law Suite?

If you can’t find a ready-made ADU that works for you—or if you already own a home—you might do better to build one yourself. This way, you get custom layouts, new finishes, and features built just for your purpose.

Who Might Build New:

• Homeowners with big lots or unused space.

• People in neighborhoods with good zoning rules.

• Those who want to earn money from rentals over a long time.

Ways to Build an ADU

Each kind of ADU has different benefits. These depend on what you want and how much space you have.

• Detached ADU (“Casita” or Tiny Home): A building completely on its own.

• Often in the backyard.

• Gives the most privacy.

• Garage Conversion: Turns an existing garage into a living space.

• Usually costs less.

• Is easier to connect to existing utilities.

• Basement Apartment: Uses existing space in a smart way to save money.

• Great for city areas where there’s not much outdoor space.

• Bump-out/Home Addition: A new part added to the main house.

• Good for older parents who need to be close by.

And every build type needs planning and permits. It also means you must follow local building codes.

How Much It Costs to Build an ADU in 2025

Source: National Association of Home Builders, 2025 Construction Projections

And some cities have faster ways to get permits or will waive fees to help people build ADUs. Check if your city offers these kinds of programs.

Timeline: Buying vs. Building

If you need a place to live or want rental money soon, buying might be quicker. But if you want a custom space for the long run, building gives you more say.

Financing: How It Works

It’s key to know how financing works for ADUs, no matter if you buy or build.

Buying a Home With an ADU

• Appraisers might add the ADU’s value to the total home value. This is especially true if the unit is legal and can be rented.

• Rental income might help you get a bigger loan.

• And loan types like FHA, VA, and Fannie Mae have different rules for ADUs.

Building Your Own

• Ways to get money include: HELOC (Home Equity Line of Credit)

• Cash-out refinance

• Renovation or construction loans

• You will likely need to give them: Approved building plans.

• Contractor quotes.

• A paper that says it meets rules.

And talk to your lender early on. This helps you know what they can and cannot fund.

Investing and Renting With ADUs

Owning an accessory dwelling unit offers flexibility. It can also be a good way to invest.

Ways to Earn Money:

• Long-term renters: Money from monthly leases.

• Short-term or vacation rentals: If local rules allow this.

• Housing for students or traveling nurses.

• Places for caregivers or independent family members.

Homes with ADUs can go up in value by 20–30%. This depends on where they are and how good the unit is.

But remember to think about how often the unit might be empty, how much it costs to manage, and what licenses you need.

Legal and Insurance Things to Think About

Besides zoning and financing, there are legal and risk issues to think about.

• Home Insurance: Not all insurance companies cover separate units or rentals. Tell your insurer so you get the right coverage.

• Responsibility: If tenants or renters don’t have insurance, you could face legal risk.

• Separate Utilities vs. Shared Systems: These can change costs, privacy, and how you bill.

• Airbnb Rules: Some cities cap short-term rentals or need special licenses.

• HOA Rules: Your homeowner association might ban or limit second units.

And if you ignore these points, you could run into permit problems or even lose insurance claims.

Taxes for Owning or Building an ADU

Your tax duties can change a lot once you own or use an ADU.

• Property Taxes: New ADUs might cause your property to be re-assessed.

• Rental Income: Any rent you get is taxable. But you might be able to deduct costs like maintenance or depreciation.

• Capital Gains: If you rent out the unit, it could change your main home’s tax break when you sell.

• Homestead Exemption: Properties used for two things might not qualify for this tax break, or they might get a smaller one.

Always talk to a licensed CPA or tax advisor. They can help your money goals match your tax plan.

Questions to Ask Before Buying a Home With an In-Law Suite

Buyer Checklist:

• Is the unit fully permitted and built to code?

• Does it meet zoning rules for short- or long-term rentals?

• Will your insurance company cover the unit?

• Is the plumbing, HVAC, and electrical system shared or separate?

• Can the expected rental income help you get financing?

• And what are the local ADU rules and any new updates from the city?

Getting these answers early helps make sure the unit can be used for a long time and follows all rules.

How Our 1% Listing Fee and Commission Rebate Can Help

We believe in clear pricing and good value, whether you’re buying or selling a property with a mother-in-law suite.

• Sellers save a lot by paying just a 1% listing fee. This is less than the usual 2.5–3%.

• Buyers might get money back at closing. This depends on state laws and what their lender needs.

• Our agents check zoning laws, permits, and if an ADU is legal. This saves you time and stress.

So why pay more when making smart real estate choices?

Should You Buy or Build?

Are you still deciding between buying a home with an ADU already there or building one yourself?

Buy If:

• You need an ADU right away.

• You want to start earning rental income sooner.

• You live in an area with strict rules where permits are tough to get.

Build If:

• You already own land or a home with a good-sized lot.

• You want a space made just for what you need.

• You are in a market with few homes for sale or high prices.

Buying or building, mother-in-law suites give you flexibility and a chance to earn money. They also help with future housing needs. Make your next move with good information and expert help.

Talk to an expert now — Your free, no-pressure chat is just one click away.

Citations:

• Pew Research Center. (2022). Financial Issues Top Reasons U.S. Adults Live in Multigenerational Homes.

• Freddie Mac Multifamily Report. (2023). Accessory Dwelling Units (ADUs): Positioning for Multifamily Potential.

• National Association of Home Builders. (2024). 2024 Construction Cost Survey.