An in-law suite—also known as an in-law apartment or accessory dwelling unit—is a small living space located on the same property as a single-family home. Originally designed to house aging parents, these suites have evolved into one of the most versatile features a home can offer.
Often equipped with a bedroom and private bathroom—and sometimes even a kitchenette or full kitchen—these suites can be attached to the main home (like in a basement or above a garage) or stand alone as separate structures.
They go by different names depending on the region: granny flat, secondary suite, ohana unit (in Hawaii), or casita (in the Southwest). Regardless of what you call them, they’re increasingly valued for their flexibility—regardless of whether you’re planning to move in a relative.
What to know about an in-law suite
The classic in-law suite is a self-contained space that offers both proximity and privacy. At a minimum, it includes:
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A sleeping area (usually a bedroom)
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A private bathroom
Many suites also feature a living room, kitchenette, or even a full kitchen. They’re ideal for aging parents, adult children, live-in caregivers, or frequent guests.
Different types of in-law suites
When not in use by an aging parent, an in-law suite can serve many purposes, making it a wise investment. Here are some uses to consider:
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Home office: “More and more buyers are looking for a place to work from home,” says Mike Dinella, broker salesperson with Lenny, Vermaat & Leonard Inc. Realtors® in Haddonfield, NJ. “So this area could be the perfect spot for your small business.”
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Guest quarters: When out-of-town guests visit, an in-law suite is the perfect place to give them a little privacy, with their own bedroom and bathroom.
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Residence for an older child: Adult children who might need to live at home while establishing themselves financially can use the space as an apartment, perhaps even paying a little rent.
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Short- or long-term rental apartment: Since many in-law suites are fully equipped apartments, they make ideal rentals, which can bring in income from long-term renters or short-term rentals on Airbnb.
Can I build an in-law suite on my property?
Local ordinances vary when it comes to the amenities of an in-law suite and its use. To find the laws specific to your property, go to the zoning office with your lot and block number to find out if having such a suite on your property is permitted.
If zoning laws do not allow an in-law apartment, it might be possible to get a variance.
“You may have to send out certified letters to the neighbors and get their signatures,” says Dinella. “The cost of a variance could run up to $500.”
You will also need to obtain building permits. Even then, there might still be limitations on what the suite can include or how it may be used. Some zoning laws do not allow full kitchens because of the risk of stove fires. Some laws do not allow such suites to be rented out if they are no longer being used for an older relative.
Bottom line: Know the local laws before investing in a home with this amenity, if you are hoping that it will become a moneymaker.
How much does it cost to build?
The cost to add this amenity to your home varies widely, depending on the size, details, and whether it will be an addition to an existing home or a stand-alone structure. When adding an in-law suite to an existing home, expect to spend an average of $30,000 to $70,000. If you’re building a new structure, it can cost as much as $125,000 (or more).