Do ADUs increase property value?
Answered by AskBaily Editorial · Updated
Short answer
Most appraisers add 60-100% of the ADU's construction cost to the property's appraised value in markets with strong rental demand. In California under AB 1033, ADUs can be sold separately as condominiums in cities that opt in, which changes the analysis — the ADU may have its own market value rather than functioning purely as an income or square-footage add-on.
In detail
There is no single percentage answer, but the research and appraisal practice converge on a few patterns:
- Rental-heavy metros (LA, SF, NYC, Seattle, Austin): appraisers routinely capitalize ADU rental income. A $35,000/year rental stream discounted at typical residential cap rates translates to $350,000-$500,000 of additional property value. In these metros, ADUs often return 70-100%+ of construction cost on appraisal.
- Lower-rent metros: the appraiser may add only the depreciated replacement cost of the ADU structure. That can mean 50-70% of construction cost added to appraised value.
- California-specific (AB 1033): starting January 2024, cities may opt in to allow ADUs to be sold separately as condominiums. Los Angeles opted in effective 2024 — meaning an LA ADU may have an independent market value rather than being bundled into the primary residence. The Freddie Mac / Fannie Mae ADU guidance allows rental income from a legal ADU to be included in mortgage qualification.
- Appraisal risk: if the ADU was built without permits, many appraisers either assign it zero value or deduct the estimated cost to legalize. The resale uplift from a permitted ADU is the biggest single reason not to go the unpermitted route.
The conservative framing: treat ADU value uplift as 60-80% of construction cost in rental-strong markets and 40-60% elsewhere, and treat rental cash flow as the real return driver rather than appraisal alone.
AskBaily's ADU scoping will flag whether your city has opted into AB 1033 and whether the lot supports a structure that can later be sold as a condo.
Sources
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