Lot Coverage Limits: Altadena vs Los Angeles
How do lot coverage limits rules compare between Altadena, CA and Los Angeles, CA?
Altadena and Los Angeles 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 →Los Angeles, CA
Los Angeles County
R1 residential floor area is capped at 45% of lot area for lots under 9,000 sq ft, and 40% (or 4,050 sq ft, whichever is greater) for lots of 9,000+ sq ft under the Baseline Mansionization Ordinance. R1 Variation Zones (R1V, R1F, R1R, R1H) have additional mass and form controls. Accessory structures count toward lot coverage. ADUs have separate size limits under state law.
View full Los Angeles rules →Key Facts Comparison
| Fact | Altadena | Los Angeles |
|---|---|---|
| Code Section | Altadena CSD 22.306.070.A.4 | LAMC Baseline Mansionization Ordinance |
| GSA Formula | 0.25 × lot area + 1,000 sf | - |
| Maximum Cap | 9,000 sq ft | - |
| Excluded From GSA | Cellars + auto garages/carports | - |
| Under 9,000 sq ft | - | Max 45% RFA |
| 9,000+ sq ft | - | Max 40% or 4,050 sq ft |
| ADUs | - | Separate state limits apply |
| Variation Zones | - | R1V, R1F, R1R, R1H mass controls |
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.
Los Angeles 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 Los Angeles zoning for your district’s maximum.
Compare other topics
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