In June, SPRI published ANSI/SPRI RP-14, "Wind Design Standard for Vegetative Roofing Systems." This new standard is intended to provide a method for designing vegetative roof systems' wind-uplift resistances. If you are involved with vegetative roof systems, I encourage you to be familiar with this standard and NRCA's concerns with it.
RP-14 is modeled closely after ANSI/SPRI RP-4, "Wind Design Standard for Ballasted Single-ply Roofing Systems." Users of RP-14 can determine the maximum allowable wind speeds for vegetative roof systems based on a specific building's height, roof edge (parapet) height and exposure category.
RP-14 addresses three specific vegetative roof system designs. For RP-14's System 1, the installed waterproofing membrane is covered with No. 4 ballast. For System 2, the roof's field is covered with No. 4 ballast and the roof's perimeter and corner regions are covered with No. 2 ballast. For System 3, the roof's field is covered with No. 2 ballast and the roof's perimeter and corner regions feature adhered or mechanically attached roof membranes.