What Is an ADU?

3 Min Read
Published Feb. 17, 2023
Father and son prepare to paint a room.
Written By
Reviewed By

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.


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.


Ready for more learning?

Here’s some other helpful articles

Related Articles

**itsHome, a LMB Mortgage Services, Inc. company, is not acting as a lender or broker. The information provided by you to itsHome is not an application for a mortgage loan, nor is it used to pre-qualify you with any lender. If you are contacted by a lender or broker advertising within our network, your quoted rate may be higher depending on your property location, credit score, loan-to-value ratio, debt-to-income ratio, and/or other factors. itsHome does not offer its matching services in all states. This loan may not be available for all credit types, and not all service providers in the itsHome network offer this or other products with interest-only options. The information that we provide is from companies which itsHome and its partners may receive compensation. This compensation may influence the selection, appearance, and order of appearance on this site. The information provided by itsHome does not include all financial services companies or all of their available product and service offerings. We use cookies to track data and provide you with the best possible experience. By proceeding you consent to the use of these cookies. For more information, see our Privacy Policy.

itsHome, a LMB Mortgage Services, Inc. company NMLS #167283, www.nmlsconsumeraccess.org