Grading & Drainage: Altadena vs Topanga
How do grading & drainage rules compare between Altadena, CA and Topanga, CA?
Topanga has fewer restrictions than Altadena.
Altadena, CA
Los Angeles County
Hillside grading exceeding 2,500 cubic yards cut + fill requires a Conditional Use Permit in Altadena (CSD 22.306.060.B.2.b). Grading during the Oct 15 – Apr 15 rainy season is subject to Public Works erosion-control requirements.
View full Altadena rules →Topanga, CA
Los Angeles County
Grading in unincorporated LA County requires permits from Building & Safety. The LA County Flood Control District manages the regional drainage system with 487 miles of channels and 2,919 miles of storm drain. Retaining walls over 4 ft require permits. Coastal areas have additional requirements for terracing and landscaping.
View full Topanga rules →Key Facts Comparison
| Fact | Altadena | Topanga |
|---|---|---|
| Code Section | Altadena CSD 22.306.060.B + LA County 22.140.240 | - |
| CUP Threshold | 2,500 cy cut + fill | - |
| Haul Route | Required ≥1,000 cy off-site | - |
| Rainy Season | Oct 15 – Apr 15 (extra controls) | - |
| Grading Permit | - | Required from Building & Safety |
| Flood Control | - | LACFCD manages regional system |
| Retaining Walls | - | Permit if over 4 ft |
| Coastal | - | Terracing and native landscaping |
Highlighted rows indicate differences between cities.
Altadena FAQ
Do I need a permit to grade my Altadena hillside lot?
Yes — a Minor Conditional Use Permit is required for any hillside development, and a full CUP if grading exceeds 2,500 cubic yards total (CSD 22.306.060.B).
Topanga FAQ
Do I need a grading permit in unincorporated LA County?
Most grading work requires a permit from Building & Safety. Exemptions exist for less than 50 cubic yards on a single lot that doesn't obstruct drainage. Contact (626) 458-3171 to confirm.
Can I change the drainage on my property?
You cannot redirect concentrated runoff onto neighboring properties. All drainage must go to approved outlets. Significant drainage changes require a grading permit and may need engineering plans.
What reports are needed for hillside grading?
Hillside projects typically require a soils report, geology report, and geotechnical recommendations. The county may require additional studies for slopes, seismic hazards, or landslide-prone areas.
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