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Green roofs are all the rage these days. Most are installed on commercial buildings to help reduce stormwater runoff and cool buildings. But homeowners who are interested in the green roof movement can also build one on a small scale. There's no need to cover your whole house. Why not a shed or even a large birdhouse? Here's how one homeowner built one on a wooden shed.
The shed is an old playhouse, custom built in the 1930's. In 2005 it was moved and the roof (including framing) was completely rebuilt and reshingled. Five years later the owner decided to add a roof garden of native plants and herbs. This was not to be a green roof for the purpose of saving on heat or water runoff, but a ' roof garden.'
 In the fall of the first year, the framing was constructed by a professional carpenter using treated 1x6 boards. Since the roof is angled, each side was divided into two sections lengthwise and holes were drilled in the long boards to aid drainage of excess water. Construction of the spine was critical, thus the decision by the owner to hire professionals to do the job. The final framework created four sections, each 2x9 feet.
 The next spring, the rest of the roof was installed. First drainage fabric was laid over the moisture barrier in each section. Then Enkadrain, a mat designed to retain moisture and deliver it upward to the medium, was cut to fit in each section. As the picture shows, the bottom side of Enkadrain has pockets made of woven plastic to hold in moisture. The next layer was Terraviva Green Roof Medium, a mixture of lightweight aggregate and organic matter based on the type of roof garden and the depth of the planting material to be used.
All this would add considerable weight - at least 2250 pounds when saturated, given the planting medium at a depth of 5 inches. Normally, a consultation with a structural engineer would be necessary to make sure the structure was adequate to bear the weight, but in this case, since the shed was all wood with a new roof (including a new frame), the owner knew the structure to be adequate for the load.
 The last step was adding plants. For this garden, they include Sky Blue Aster, Lamb's Ears , Dianthus, Dragon's Blood Sedum, Prairie Dropseed , Geranium 'Max Frei', Coreopsis 'Moonbeam', and the following herbs: Chives, Marjoram, Oregano, Sage and Thyme. The gardener's intent was to create a roof garden, vibrant with plants and color, not a 'green roof,' a mat of groundcovers planted primarily to provide a living, green surface.
 The garden was planted in early May, a very cool month in 2011. It has been watered daily in hot weather and at least every other day in cooler weather, unless rain does the job. As of the end of July, the Prairie Dropseed, Sky Blue Aster, Coreopsis, and the herbs were doing the best, even on the side of the roof exposed to the harsh sun of a record-setting hot July.
Thanks to Sage Advice for providing the photos for this issue! |
