Abstract: A multilayer assembly (10) for use in a vegetated eco-roof or wall system includes layers of progressively permeable geomatrix material. Preferred embodiments of the multilayer assembly are composed of a filtration layer (22) of a nonwoven type positioned between a three-dimensional drainage/aeration base layer (24) and a growing media support layer (26). The sizes and structures of the pores of the base layer, openings of the filtration layer, and pores of the growing media support layer cooperate to permit flow of liquid from the growing media support layer through the base layer and form a gas flow gradient throughout the multilayer assembly. The gas flow gradient permits passage of gas from the base layer to the growing media support layer to mitigate moisture accumulation at the base layer.