Usually, a permitted ADU adds value, but there is no fixed percentage. Appraisers compare recent sales of similar homes with ADUs and may weigh rental income. FHFA data shows California homes with ADUs had a 2023 median appraised value of $1,064,000, versus $715,000 without, though that gap reflects many factors, not the ADU alone.
What does the appraisal data show?
The Federal Housing Finance Agency looked at California single-family purchase loans backed by Fannie Mae and Freddie Mac, in a post published January 2, 2025:
- 2013 median appraised value: $550,000 with an ADU, $405,000 without.
- 2023 median appraised value: $1,064,000 with an ADU, $715,000 without.
- Annual growth, 2013 to 2023: 9.34% with an ADU, 7.65% without.
FHFA warns the ADU data is limited and may include appraiser entry errors. Homes with ADUs may also differ from homes without them in other ways, such as lot size and location. These numbers describe a pattern, not the value an ADU will add to your house.
How do appraisers value an ADU?
Mainly with comparable sales. When ADU rental income is used to qualify for a loan, Freddie Mac requires a full appraisal with at least one comparable sale of a property with an ADU and at least one comparable rented ADU. The report must describe the ADU's condition, finished square footage and rooms.
In practice, a well-built, permitted unit with its own entrance, kitchen and bathroom gives an appraiser more to work with than a converted room.
Will building an ADU raise my property taxes?
Yes, for the new part only. Under Proposition 13, the county assessor adds the value of the new construction. Your existing home keeps its current assessed value. The added value can then rise up to 2% per year like the rest of your assessment. The Los Angeles County Assessor handles Long Beach, Lakewood, Signal Hill and Downey; the Orange County Assessor handles Seal Beach.
Does an unpermitted ADU add value?
Much less reliably. Lenders and appraisers look for legal units. Freddie Mac does not allow rental income from illegal ADUs to be used to qualify, and requires the ADU to meet zoning rules when rental income is used. Long Beach's draft ADU ordinance aims to formalize how unpermitted units can be legalized, as of October 2026.
Can I sell the ADU separately?
Usually not. As of October 2026, state law lets a city choose to allow an ADU and the main home to be sold separately as condominiums, but only if the city adopts that option. We have not found that Long Beach has done so, so plan on the ADU and the house selling together.
When does it depend?
It depends on your neighborhood, the ADU's quality and how buyers there use extra units. A unit that fits buyers in your area, whether for rental income, family or a home office, is easier for an appraiser to support with comparable sales. Build cost and added value are different numbers; one does not guarantee the other.
Related
Sources, as of October 2026: FHFA, "Trends in Median Appraised Value for Properties With Accessory Dwelling Units in California" (January 2, 2025); Freddie Mac ADU fact sheet; Howard Jarvis Taxpayers Association on ADU reassessment; California Government Code §66342; City of Long Beach ADU page.
Updated October 2026