Several years ago, we bought an extra-large home in an inner-city neighborhood, which had a separate apartment on the third floor.

We felt that the comfortable third-floor space, with its terrific territorial view, was one of the big amenities of this big house. It could be reached from the interior of the house or from a convenient separate entry off the driveway.

The idea was to rent the apartment to help with the hefty monthly mortgage or to swap the space for nanny services. The only problem was that there was no stove to heat the space.

One afternoon a young woman named Abby pulled up in a high-mileage, orange VW bug and asked if we had already rented our third-floor apartment. Abby said she had rented the apartment before and knew all the do’s and don’ts of coming and going to a third-floor apartment — especially when young children were sleeping on the floor below. She also said the space was illegal.

At the time, our apartment, like most of the estimated 50,000 mother-in-law apartments in the city, zoned single-family, was "nonconforming." Since we left, the new owners obtained a permit for the "accessory dwelling unit," or ADU. Now, while building codes vary, many jurisdictions allow one ADU per single-family residence.

ADUs have become extremely helpful. Not only do they give adult children a less expensive and safer way to keep an eye on the folks, ADUs also have provided needed shelter for caregivers or family members unable to afford a home or apartment of their own. Income from ADUs often helps ease difficult financial situations, especially retired folks who need help to pay high property taxes. The apartments also would be an attractive option for seniors on a limited income and other low-income residents.

When homeowners do the research on how to construct a workable ADU space — be they apartment carriage houses, cottages or casitas — it’s also best to know how many people can live there before you break ground or knock down walls.

There are stipulations for accessory housing, but the one most discussed is the number of people who can occupy the accessory unit. A typical code might read "The total number of people who may occupy principal residence and the accessory unit, together, shall not exceed the number of people who may occupy a single-family dwelling. …"

The definition of family can mean "an individual, or two or more persons related by blood or marriage, or a group of not more than eight persons who are not related by blood or marriage, excluding servants, living together in a dwelling unit." But what about minors? Are they included, or can there be any number of offspring allowed because they are related by blood?

One Puget Sound, Wash.-area resident moved from her home in a multifamily, business-zoned area to a single-family-zoned area because the traffic and noise had become too much for her to handle. After about three years at her new address, she started experiencing some of the same problems that led her to move. This time, they were right next door.

"The basement had been totally renovated with its own separate entrance," she said. "There were now two separate units and one was being rented to three young men in the construction business. There were extra cars being parked on the street, and the congestion and noise were becoming a problem."

She spoke to other neighbors who also felt the same way. When she went to the library and discovered any homeowner could apply for "accessory housing," she was shocked.

"I thought it was crazy that there is no real single-family zoning," she said. "As long as it’s owner-occupied, you can put in a mother-in-law apartment. The only reason it’s not classified a duplex is that the owner lives there."

I bet if you polled the employees in most building departments you would get a variety of answers and find confusion about the number of people who could occupy a single-family residence with an accessory unit.

Some jurisdictions classify an ADU "as its own dwelling unit" and can accommodate an entirely different family than the one living in the principal dwelling. Some stipulate a specific number that includes minors.

If you are planning to buy or rent in a single-family neighborhood, spend a lot of time talking to neighbors about the area and your new block in particular. Take a lunch hour and watch traffic. Then take a dinner hour and do the same. Finding out what’s up now could make your future a lot more pleasant.

If you planning to add an ADU, consider something close to the original connotation of mother-in-law apartments. Maybe that’s how they got their name.

Show Comments Hide Comments


Sign up for Inman’s Morning Headlines
What you need to know to start your day with all the latest industry developments
By submitting your email address, you agree to receive marketing emails from Inman.
Thank you for subscribing to Morning Headlines.
Back to top
Only 3 days left to register for Inman Connect Las Vegas before prices go up! Don't miss the premier event for real estate pros.Register Now ×
Limited Time Offer: Get 1 year of Inman Select for $199SUBSCRIBE×
Log in
If you created your account with Google or Facebook
Don't have an account?
Forgot your password?
No Problem

Simply enter the email address you used to create your account and click "Reset Password". You will receive additional instructions via email.

Forgot your username? If so please contact customer support at (510) 658-9252

Password Reset Confirmation

Password Reset Instructions have been sent to

Subscribe to The Weekender
Get the week's leading headlines delivered straight to your inbox.
Top headlines from around the real estate industry. Breaking news as it happens.
15 stories covering tech, special reports, video and opinion.
Unique features from hacker profiles to portal watch and video interviews.
Unique features from hacker profiles to portal watch and video interviews.
It looks like you’re already a Select Member!
To subscribe to exclusive newsletters, visit your email preferences in the account settings.
Up-to-the-minute news and interviews in your inbox, ticket discounts for Inman events and more
1-Step CheckoutPay with a credit card
By continuing, you agree to Inman’s Terms of Use and Privacy Policy.

You will be charged . Your subscription will automatically renew for on . For more details on our payment terms and how to cancel, click here.

Interested in a group subscription?
Finish setting up your subscription