In 2008, Greensgrow began to install living roofs on most of our permanent structures. Living roofs or green roofs are lightweight plant-based systems that can capture and utilize rainwater at the point of first contact, the roof, while also increasing the insulation value of the structure.
Because our farm is located on a brownfield site that has been capped with concrete, rainwater has few places to go since there is little soil to absorb the water. This is a particular problem in Philadelphia where the storm drains and sewers are connected in a Combined Sewer Overflow (CSO) system. In times of heavy rain, there is too much water for the treatment plants to handle, sewage and other pollutants can end up directly in the river. Depending on the depth of the soil medium and the type of plant material, some living roofs can capture almost all of the rainfall that occurs in a storm. This means less water in the storm drain and less pollutants in the river.
There are several companies in our area that design and install living roof systems on commercial and residential buildings, and these systems have become very popular in recent years particularly because of their insulating properties. Chicago in particular has become famous for constructing living roofs on municipal buildings, including City Hall. The cost of installing a living roof however can be quite high. Here at Greensgrow we have been experimenting with cheap and lightweight systems that utilize surplus and easily-available materials in an effort lower costs.
The Greensgrow model uses plant trays and perlite as its main ingredients, on top of a primary layer of EPDM roofing, sheet plastic, and pea gravel. The top layers are a blend of compost, pine bark, perlite, and topsoil to provide suitable growing conditions. In the living layer, we have planted drought-tolerant sedums and grasses, plus native wildflowers to attract beneficial insects and wildlife.