How to Build a Lightweight Food-Producing Green Roof
Rooftop farms may be stealing the lime light from green roofs, but there's still a lot to be said for putting plants on rooftops to filter rainwater, regulate building temperatures, promote biodiversity and counter the urban heat island effect. Most green roofs we hear about tend to be gigantic installations like Wal-Mart's Chicago green roof, partially because DIY green roofs on existing buildings run the risk of structural damage and even collapse. Nevertheless, Kevin Songer has posted a design for a living, food-producing green roof on a storage shed at an urban Florida farm which, he says, was built to withstand hurricanes:
Rafters are made from electrical conduit, though next time bamboo - a much more sustainable material - will be used to replace the conduit. Rather than using a roofing material like tin, the rafters are covered with farm fencing. A tarp is strapped to the top of the farm fencing, acting as a waterproofing layer and partial support for the green roof soil and plants. One of the interesting aspects of the tarp and the fencing is the ability of the tarp to form a small indentation in-between the fencing runs, allowing for water to collect during a rainfall event and acting as mini-storage reservoirs for the roof.
A layer of rough ground organic material such as small branches, bamboo pieces and other bulky material was added to the top of the tarp for drainage facilitation. Lightweight, high-organic content green roof soil media completed the green roof layer preparation and the pre-sprouted cow-peas added as the final green roof touch.
Given the apparently experimental nature of this project, we're kind of glad that it is on a storage shed, not a dwelling. We'll be watching with interest to see how the thing holds up. In the meantime, don't try this at home without consulting a professional.