Cell-Tek Geosynthetics. The SlopeGrid geocellular confinement system allows for green roofs on arched or sloped roofs by controlling erosion, promoting stabilization of the planting medium, and preventing vertical wind uplift, the firm says. Installed over a waterproofing membrane and a drainage/water retention mat, the 100% recycled HDPE strips expand into a honeycomb-like grid, which is filled with soil. The grid is secured to the roof by a tendon system. 888.851.0051. www.celltekdirect.com.