North Carolina Green Roof Minimum Design Criteria

The purpose of this Rule is to set forth the design requirements for green roofs that are constructed to meet the requirements of this Section.
(1) MEDIA SPECIFICATION. The maximum organic fraction of the media shall be 10 percent by volume.
(2) DESIGN VOLUME. The design volume for a green roof shall equal the media depth times the plant available water (PAW). The maximum rainfall depth that may be treated by a green roof shall be 1.5 inches.
(3) MINIMUM MEDIA DEPTH. The minimum media depth shall be four inches if the roof will not be irrigated or three inches if the roof will be irrigated. For roofs with three-inch media depths, an irrigation plan shall be included in the Operation and Maintenance Plan.
(4) VEGETATION SPECIFICATION. The planting plan shall be designed to achieve a 75 percent vegetative cover within two years.
(5) SLOPE. The green roof shall have a slope (or pitch) of no greater than eight percent.