Retaining Walls: Mililani Mauka vs Urban Honolulu
How do retaining walls rules compare between Mililani Mauka, HI and Urban Honolulu, HI?
Urban Honolulu has fewer restrictions than Mililani Mauka.
Mililani Mauka, HI
Honolulu County
ROH Sec. 21-4.40 limits fill-retaining walls in Mililani Mauka yards to six feet and combines terraced wall heights, important on the community's sloped Central Oahu grades.
View full Mililani Mauka rules →Urban Honolulu, HI
Honolulu County
Urban Honolulu limits retaining walls that contain fill within required yards to 6 feet under ROH 21-4.40 and combines terraced wall heights to prevent stacking around hillside lots.
View full Urban Honolulu rules →Key Facts Comparison
| Fact | Mililani Mauka | Urban Honolulu |
|---|---|---|
| - | - | |
| Max height | - | 6 feet |
| Terracing rule | - | Combined height |
| Permit trigger | - | Over 30 inches |
| Code section | - | ROH 21-4.40 |
Highlighted rows indicate differences between cities.
Mililani Mauka FAQ
Can I build a three-tier terrace instead of one tall wall?
Terraced walls are measured together under ROH 21-4.40, so stacking tiers does not sidestep the six-foot limit.
Must retaining wall finishes be approved by MTA?
Yes. Walls visible from the street typically require MTA approval for color and finish.
Urban Honolulu FAQ
How tall can a retaining wall be in Urban Honolulu?
Under ROH 21-4.40, retaining walls containing fill within required yards cannot exceed 6 feet. Terraced walls on hillside lots in neighborhoods like Manoa are measured as one combined wall.
Does a hillside retaining wall need a permit in Honolulu?
Yes, if it exceeds 30 inches. ROH 18-3.1 exempts only walls 30 inches or shorter. Honolulu DPP typically requires engineered plans, drainage, and guardrails for larger hillside retaining walls.
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