Maui County Zoning Ordinances include provisions for Planned Development and Lot Reduction, Open Space Incentives, and Cluster Development Overlay Zones. Planned Development is intended to encourage better design and land use, protect the natural environment, minimize traffic congestion, and improve living conditions. At least 20% of Planned Developments must be preserved as protected open space and designed as a park-like area. Lot reductions of 20% and multi-unit buildings are permitted in these developments, specific numbers depending on underlying zone. Open Space Incentives provide additional floor space or building height in return for the provision of open space in a development beyond the minimum yard setback required for the project. In addition, additional floor space may be granted for installing underground parking areas, instead of surface parking. Tops of underground parking structures must be landscaped with no more than 1/3 of the area left unvegetated. Cluster Housing is designed to allow land use flexibility, innovative design, open space, minimum grading due to private and narrower roads, and common amenities. Clustered developments may have multi-unit residences, and no more than 15% of the land area may be covered by buildings.