Lot Coverage Limits: Altadena vs Downey
How do lot coverage limits rules compare between Altadena, CA and Downey, CA?
Altadena and Downey have similar restriction levels.
Altadena, CA
Los Angeles County
Altadena R-1 max Gross Structural Area (GSA) and lot coverage = (0.25 × net lot area) + 1,000 sq ft, never exceeding 9,000 sq ft total (Altadena CSD 22.306.070.A.4).
View full Altadena rules →Downey, CA
Los Angeles County
Lot coverage in Downey is regulated by zone. No building may occupy a greater percentage of lot area than specified for its zone. Open space required for one building cannot count toward another.
View full Downey rules →Key Facts Comparison
| Fact | Altadena | Downey |
|---|---|---|
| Code Section | Altadena CSD 22.306.070.A.4 | - |
| GSA Formula | 0.25 × lot area + 1,000 sf | - |
| Maximum Cap | 9,000 sq ft | - |
| Excluded From GSA | Cellars + auto garages/carports | - |
| Coverage | - | Per zone maximum |
| Open Space | - | Cannot share between buildings |
| Yards | - | Per zone requirements |
| Code | - | Article IX Zoning Ordinance |
Highlighted rows indicate differences between cities.
Altadena FAQ
How big a house can I build on a 10,000-sq-ft Altadena lot?
Maximum GSA = 0.25 × 10,000 + 1,000 = 3,500 sq ft (excluding garage and cellar). The absolute cap is 9,000 sq ft on any lot.
Downey FAQ
What counts as lot coverage?
All impervious surfaces: buildings, garages, driveways, patios, and walkways. Permeable pavers may be partially excluded.
How do I calculate my lot coverage?
Divide total impervious surface area by total lot area. Check Downey zoning for your district’s maximum.
Compare other topics
See how Altadena and Downey compare on other ordinance categories.
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