ADU Rules: Altadena vs Santa Monica
How do adu rules rules compare between Altadena, CA and Santa Monica, CA?
Altadena and Santa Monica have similar restriction levels.
Altadena, CA
Los Angeles County
Altadena is an unincorporated CDP in Los Angeles County governed by LA County Code Title 22 §22.140.640 (Accessory Dwelling Units and Junior Accessory Dwelling Units), most recently amended April 2024. Single-family lots may add one ADU plus one JADU; multifamily lots may add up to two detached new-construction ADUs plus conversion ADUs in non-livable existing space.
View full Altadena rules →Santa Monica, CA
Los Angeles County
Santa Monica regulates ADUs under SMMC §9.31.025. Maximum size is 650 sq ft on lots up to 6,000 sq ft or 800 sq ft on larger lots. No development fees. Ministerial approval process.
View full Santa Monica rules →Key Facts Comparison
| Fact | Altadena | Santa Monica |
|---|---|---|
| Governing Code | LA County Code §22.140.640 | - |
| Single-Family | 1 ADU + 1 JADU per lot | - |
| Multifamily Detached | Up to 2 new (20 ft max) | - |
| WUI Fire Zone | Chapter 7A applies (hillside) | - |
| Side/Rear Setback | 4 ft (new construction) | - |
| Code Section | - | SMMC §9.31.025 |
| Max Size (small lot) | - | 650 sq ft (lots ≤6,000 sf) |
| Max Size (large lot) | - | 800 sq ft (lots >6,000 sf) |
| Setbacks | - | 4 feet rear/side (new) |
| Dev Fees | - | None |
Highlighted rows indicate differences between cities.
Altadena FAQ
Who regulates ADUs in Altadena?
Altadena is unincorporated, so LA County Regional Planning regulates ADUs under LA County Code Title 22 §22.140.640, not a separate city ordinance.
Do hillside or fire rules apply to Altadena ADUs?
Yes. Altadena's hillside neighborhoods are in LA County's Very High Fire Hazard Severity Zone, requiring Chapter 7A ignition-resistant construction and Fire Code §325 brush clearance. Hillside-grading provisions of Title 22 apply on slopes steeper than 10%.
How big can my Altadena ADU be?
Under §22.140.640, a detached ADU on a single-family lot may be up to 1,200 sq ft; multifamily-lot ADUs have no maximum size cap. JADUs are capped at 500 sq ft.
Santa Monica FAQ
Can I build an ADU on my property in Santa Monica?
Santa Monica regulates ADUs under SMMC §9.31.025. Maximum size is 650 sq ft on lots up to 6,000 sq ft or 800 sq ft on larger lots. No development fees. Ministerial approval process.
What are the size limits for an accessory dwelling unit in Santa Monica?
Code Section: SMMC §9.31.025. Max Size (small lot): 650 sq ft (lots ≤6,000 sf). Max Size (large lot): 800 sq ft (lots >6,000 sf). Setbacks: 4 feet rear/side (new).
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