ADU Rules in Altadena.
Local ADU regulations, permit fees, setback requirements, and typical timelines for Altadena. Last updated 2026-05-27.
Altadena ADU Requirements
LA County Department of Regional Planning rules apply — state minimums.
Attached ADU: up to 25 ft
Metro bus and proximity to Pasadena transit network.
Permits issued by LA County Building & Safety (LACBS), not a city building dept.
Design 4 weeks · Permit 6 weeks · Build 36 weeks
Plain-language summary
In Altadena, a detached ADU requires a minimum 4-foot side setback and 4-foot rear setback. The maximum height for a detached ADU is 16 feet, while an attached ADU may be up to 25 feet. The maximum size for a detached ADU is 1,200 sq ft; a Junior ADU (JADU) is limited to 500 sq ft. Replacement parking is not required for most projects. Typical permit fees range from $6,000 to $12,000. A typical project takes approximately ~11 months from design start to move-in, including 4 weeks of design, 6 weeks for permit review, and 36 weeks of construction.
⚠️ ADU rules change frequently. Always verify current requirements with the Altadena Building & Safety Department before submitting plans. Official source →
What to Watch Out For
- Altadena is an unincorporated community governed by Los Angeles County — permits go through LA County Building & Safety (LACBS) and the Department of Regional Planning (DRP), not a city building department.
- VHFHSZ applies to the mountain-facing portions of Altadena; fire-resistant construction required.
- Altadena has no city HOA requirements, but individual CC&Rs may exist in some tracts.
- Post-Eaton Fire (Jan 2025): many parcels are in the fire rebuild zone — LA County has expedited permit review pathways available.
How Long Does It Take to Get an ADU Permit in Altadena?
Site study, floor plans, elevations, structural drawings.
Plan check, corrections, and permit issuance by Altadena Building & Safety.
Foundation, framing, MEP rough-in, finishes, final inspection.
A licensed engineer on your lot, free.
30 minutes. We walk the property, figure out what's feasible, and answer any questions you have.
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