Drainage Materials

Adequate drainage is essential to maintain effective waterproofing, the structural system’s integrity, the survival of the plants, and durability of site elements such as walls and paving. There must be a way (preferably with built-in redundancies) to collect, absorb, direct, and distribute water throughout the entire landscape system.

Living green roofs are intended to detain at a minimum the initial 0.5 to 1 inch of rain- fall of the most frequently recurring storms in a given region. Water beyond the absorption and storage capacity of the living green roof system must be directed to drainage outlets and released. For landscapes over structure, excess water from rain or irrigation must be released by directing it through surface or subsurface drains to the stormwater system. As discussed previously, standing water in soil leads to the depletion of oxygen and the creation of anaerobic conditions as well as deterioration of inert components and potential system-wide failure.

The drainage layer can be a single medium or component or a combination of components to facilitate the positive flow of excess water. To filter and delay runoff, the drainage system should be continuous across the top of the waterproofing membrane. The thickness of the drainage layer and the materials used to accomplish adequate drainage may differ; like all other components and systems, drainage systems need to be evaluated for the most appropriate applications to specific conditions.

Adequate drainage increases the ability of air to flow through the soil or growing medium and lessens the potential for detrimental anaerobic conditions. Airflow helps to maintain a healthy soil environment, which includes beneficial soil bacteria and worms, by allowing more pore space for root growth and development. Air may be incorporated into
the soil by combined use of materials that are usually associated with drainage compo- nents. Some mats facilitate both drainage and aeration.

1. Stone Drainage Aggregates
2. Lightweight Drainage Aggregates
3. Synthetic Drainage Components and Composite Drainage Products
4. Drainage Panels
5. Aeration Mats and Panels
6. Moisture Retention Mats
7. Filter Fabrics
8 .Drains