What an ADU costs in Downey (2026)
Downey runs its own ADU permits and has pre-approved plans for detached ADUs. Here are typical numbers, the local rules, and your next step.
Typical ADU numbers in Downey
- 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 $3,750 a month for 750 sq ft.
- Home value nearby: about $650 per sq ft (County median area).
Run the free ADU and new home cost calculator for Downey
ADU permits and local rules in Downey
Who runs permits
City of Downey Community Development: Planning and the Building and Safety Division, with Downey Fire and Public Works.
Pre-approved ADU plans
Yes. Downey has pre-approved standard plans for detached ADUs. You buy them from the designer, and the city still checks your site.
What can slow you down
- Grading, solar and fire sprinklers need separate permits.
- Fire and Public Works also review each project.
Sources: City of Downey Pre-Approved Standard Plans for Detached ADUs page. State ADU law. General information, not legal advice. Updated October 2026.
Free lot check in Downey
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.
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