Retaining Walls: Honolulu vs Mililani Town
How do retaining walls rules compare between Honolulu, HI and Mililani Town, HI?
Honolulu has fewer restrictions than Mililani Town.
Honolulu, HI
Honolulu County
Honolulu's LUO Section 21-4.40 limits retaining wall heights in required yards to 6 feet when containing fill and combines terraced wall heights for measurement purposes island-wide.
View full Honolulu rules →Mililani Town, HI
Honolulu County
Mililani Town retaining walls follow ROH Sec. 21-4.40 rules and HOA review. Fill-retaining walls in required yards cannot exceed 6 feet, and terraced walls are measured in combination.
View full Mililani Town rules →Key Facts Comparison
| Fact | Honolulu | Mililani Town |
|---|---|---|
| Max in required yard | 6 feet | - |
| Terracing rule | Combined heights counted | - |
| Permit trigger | Over 30 inches | - |
| Code section | ROH 21-4.40 | - |
| - | - |
Highlighted rows indicate differences between cities.
Honolulu FAQ
How tall can a retaining wall be in Honolulu County?
Under ROH 21-4.40, retaining walls containing fill within required yards cannot exceed 6 feet. Terraced walls are combined for measurement, so stacking shorter walls does not avoid the limit.
Do retaining walls need a permit in Honolulu?
Retaining or riprap walls 30 inches or shorter are exempt under ROH 18-3.1. Taller retaining walls require a Honolulu DPP building permit and often engineered drawings.
Mililani Town FAQ
Do planter walls count as retaining walls?
If they hold back soil, yes; decorative low planters that don't retain earth are typically not regulated under 21-4.40.
Is HOA approval needed for a 24-inch garden wall?
Usually yes. Even ROH-exempt walls typically still need HOA architectural review in Mililani before construction.
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