Green Roofs part 1 What is a green roof?

     The other day I was climbing on a ladder in my backyard to get plums to make jam when I looked over at my roof and thought Could I make that a green roof? The main pitch of the roof is too steep but the laundry/storage room that was built onto the back has much less pitch to it. This is a shot of my roof.

     The back section of my roof looks promising as a green roof but it will never be as cool as this school in Singapore.

 Above: Nanyang Technological University School of Art and Design in Singapore
Below: Meera Sky Garden House, Singapore

 Check out more cool green roofs at http://www.hometownroofingcontractors.com/blog/11-stunning-green-roofs-may-turn-rush-limbaugh-into-tree-hugger  

     Currently, most green roofs in the US are on commercial buildings, government or university buildings or apartment complexes. Green roofs on a single family house are just not that common. There may be a number of factor which contribute to this fact but let's first look at what a green roof is.
What is a "Green Roof"?
     I use to call any roof with plants on it a 'green roof'. Even if it was more of a roof patio with planters. But an actual green roof has to have the growing medium (aka dirt) directly on the roof and not separately contained in planters. Roof top patios and gardens are super awesome but they are not considered green roofs, aka living roofs, eco-roofs or vegetated roofs.
     There are two kinds of green roofs. Intensive and extensive. Intensive green roofs have a deeper growing medium and can grow more substantial plants such as trees and shrubs. Those cool pictures you see of rooftop gardens in Brooklyn where the restaurant grows all its own vegetables are examples of intensive green roofs. The goal for these roofs are usually the plants themselves which are grown for food or to create a beautiful space.

      This is a photo of Higher Ground Farm, a rooftop garden in Boston (http://higher-ground-farm.com/).

     Extensive green roofs have much less growing medium, about 2-6 inches usually. The goal of this type of roof is to provide insulation for the building as well as reduce storm water runoff. The plants are usually native grasses or other plants that can thrive with little to no care and have shallow roots. The traditional sod roof houses in Norway are extensive green roofs.

      This is a house in Iceland with a traditional sod roof. You can learn more about the history of green roofs here http://www.greenroofs.com/Greenroofs101/history.htm.

     Even though the aim of intensive vs extensive green roofs are slightly different both have many of the same benefits. Besides being pretty the benefits include:
     *Management of rainwater- A green roof will trap and hold a significant amount of rainwater which will keep it from draining into gutters and reducing the risk of flooding.
     *Cooling and energy conservation- All that extra dirt and material adds insulation to a roof keeping a house warmer in the winter. In the summer the plants absorb the sun instead of a traditional black shingle roof which just heats up in the sun.
     *Increase biodiversity/ providing wildlife habitat- This all depends on what you plant on your green roof but it could be easily geared toward creative an inviting environment for birds and other wildlife.
     *Noise insulation- More of an issue for in the big city but it does offer some soundproofing.
     *Waste water treatment- Nature is great at filtering water and a green roof is no exception. The rainwater that does drain off a green roof will be slightly filtered of some contaminates. Also, you could spray your green roof with gray water from your house and have the roof filter out the larger particulates.
     *Food production- Of course a roof top garden will make food for us but a flowering extensive roof can make food for other animals. A roof full of clovers and a bee hive make a perfect pair.

     A green roof is not super complicated but it does take some good planning and a strong back.

     So there are 7 layers in a green roof. The structural support can be the roof itself if it is strong enough. Most are not because they are not designed to have all this other stuff on it but roofs in more northern climates with heavy snow fall might have enough integrity to just throw a green roof on. Consult an engineer before you go crazy.
     The roofing membrane is what usually goes under roofing shingles and is waterproof. A basic protective layer. The protective membrane/root barrier is a but stronger and keeps the waterproof layer from getting damaged. The insulation gives even more protection to the lower layers and helps insulate the house. The drainage, aeration and water storage layer is very important because it does exactly what is says. Because the growing medium can be very thin there is not a lot of space for excess water to accumulate. This layer will help the soil drain so the plants don't get water logged but will also retain some water for later use.
     Finally we have the growing medium which can be rich thick soil for growing vegetables or a light thin sandy layer good for hardy plants which cover in a thin layer. Know what plants you want to grow first and that will dictate your growing medium as well as how much structural support you need.
     You might be able to alter this setup a little bit. I doubt the traditional sod roofs of Norway have the fancy insulation or drainage layers. And the cactus covered roofs of the southwest probably don't need the insulation. So consult a permaculture expert in your area to see what you need for the type of green roof you want.
     Feeling excited about making a green roof? My next post will be about implementing a green roof as well as design ideas and small projects that anyone can do.