What Is an ADU?

Some homeowners build separate and independent living spaces on their properties, often for older relatives to live in. Sometimes known as mother-in-law suites, such spaces are legally called an accessory dwelling unit, or ADU.

What is an accessory dwelling unit? The law defines an accessory dwelling unit as a separate, independent living space located on the same lot as a single-family home. An ADU can be added either by converting part of an existing home or by building a detached, separate structure.

ADUs can come in handy as an affordable and convenient housing solution for older relatives who wish to maintain some independence. ADUs also can be rented out to unrelated tenants — either in the short term or long term — generating an additional stream of income for the property owner.

Primary ADU Requirements

Many government agencies offer homeowners help to finance and build an ADU. However, the unit will need to meet certain requirements:

• Unit size. The unit must be smaller than the primary home on the property.
• Full kitchen. The kitchen must include a sink with running water, cabinets, countertops, and a stove or stove hookups. Microwaves, hot plates, and toaster ovens don’t count as a substitute for the stove.
• Full bathroom. The unit must have a private toilet and bathing area.
• Private entrance. The unit must have its own private entrance so that whoever lives there can enter and exit without having to go through the main home.
• Zoning. There can only be one ADU on the property.

Utilities

The utilities for an ADU typically are included in the primary home’s service. Homeowners who plan to rent out their ADU may include the estimated cost of utilities in the rent they charge. However, some areas and utility providers may allow separate utility connections for ADUs that let the tenant pay for their own utilities.

Homeowners Association

If the primary home is part of a homeowners association, any ADUs you plan to add will need to adhere to its regulations. If you intend to rent out your ADU, be sure it’s allowed under your HOA rules.

FAQ: What Is an ADU?

Here are answers to some frequently asked questions about ADUs.

What are the pros and cons of an ADU?

An ADU can be a long-term housing solution for older relatives, or a guest room or short-term rental. Even better, adding an ADU can increase the value of your home.
However, ADUs cost money to build and maintain. If you rent out your ADU, you’ll be taking on added costs and liabilities. If you depend on the income from an ADU, vacancies can cost you money.

Can I Airbnb my ADU?

Unless you belong to an HOA that prohibits the practice, you should be free and clear to rent out your ADU on Airbnb or another short-term rental platform.

Are ADUs worth the investment?

ADUs can increase your property’s value by adding to your home’s square footage and increasing the number of bedrooms and bathrooms it has. ADUs also can be considered an affordable type of home to construct because you can build them on land you already own. If you plan on renting out your ADU, the income can help you pay for the cost of building it, and eventually turn a profit.