What an ADU costs in Altadena (2026)
Altadena is not a city. It is unincorporated LA County, so the County runs permits. Here are typical numbers, the local rules, and your next step.
Typical ADU numbers in Altadena
- A 750 sq ft backyard ADU with a standard finish costs about $300,000 to build, all in: building, site work, city fees and design.
- Typical ADU rent: about $4,300 a month for 750 sq ft.
- Home value nearby: about $850 per sq ft (Close-in area).
Run the free ADU and new home cost calculator for Altadena
ADU permits and local rules in Altadena
Who runs permits
LA County Public Works (building permits, on EPIC-LA) and Regional Planning (zoning).
Fire rebuild help
For Eaton Fire rebuilds, the County offers pre-approved plans, a self-certification option, and fee deferrals or refunds for homes the owner lived in. There's a One-Stop Permit Center in Altadena.
What can slow you down
- Much of Altadena is in a high fire zone. New homes there need fire-resistant building.
- New state rules will ban burnable things within 5 ft of homes (Zone 0).
- SB 9 lot splits are paused in the burn area for now.
Sources: recovery.lacounty.gov (fee deferrals, self-certification); LA County Public Works. State ADU law. General information, not legal advice. Updated October 2026.
Free lot check in Altadena
Send Hemisphere A&E your address. We look up your zoning and lot size, what fits (ADU, junior ADU, SB 9, new home, apartments, remodel or business space), red flags like fire zones or hillside rules, and a rough cost range. No cost, no pressure. Email info@hemisphereae.com or call (619) 762-7144.
More cost guides for Altadena
- What a new home costs in Altadena
- What a restaurant, shop or office build-out costs in Altadena
- What an apartment building costs in Altadena
Cost guides for more of LA County
- What an ADU costs in Alhambra
- What an ADU costs in Arcadia
- What an ADU costs in Beverly Hills
- What an ADU costs in Burbank
- What an ADU costs in Culver City
- What an ADU costs in Downey
- What an ADU costs in Eagle Rock
- What an ADU costs in El Segundo
- What an ADU costs in Glendale
- What an ADU costs in Hawthorne
- What an ADU costs in Highland Park
- What an ADU costs in Inglewood
- What an ADU costs in Lancaster
- What an ADU costs in Long Beach
- What an ADU costs in Malibu
- What an ADU costs in Manhattan Beach
- What an ADU costs in Mar Vista
- What an ADU costs in Pacific Palisades
- What an ADU costs in Pasadena
- What an ADU costs in Redondo Beach
- What an ADU costs in Santa Clarita
- What an ADU costs in Santa Monica
- What an ADU costs in Sherman Oaks
- What an ADU costs in South Pasadena
- What an ADU costs in Torrance
- What an ADU costs in Venice
- What an ADU costs in West Hollywood
- What an ADU costs in Westchester
- What an ADU costs in Whittier