Retaining Walls: Honolulu vs Mililani Mauka
How do retaining walls rules compare between Honolulu, HI and Mililani Mauka, HI?
Honolulu has fewer restrictions than Mililani Mauka.
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 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 →Key Facts Comparison
| Fact | Honolulu | Mililani Mauka |
|---|---|---|
| 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 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.
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