A Little Green Roof

As I mentioned in my last blog, we have recently moved house, and I have to say the just about the best part of this has been that we are building a design studio in the back garden so that I can work at home, but still be separate from the relative chaos of life with three little kids.

We had a lot of fun designing the studio, and we found some great websites. Our favourite website is moderncabana.com, which ships its pretty cabanas in kits to homeowners for assembly. We liked their designs and were inspired by them, but we wanted to build the studio ourselves.

One of the features that we really wanted for the studio was a green roof rather than conventional roofing. Though the studio is tiny (just 86sq'), a planted roof still has many benefits, including decreasing run-off, regulating the temperature inside the studio, and of course a planted roof is infinitely nicer to look at than asphalt shingles.

On a larger scale, green roofs in cities can drastically decrease the amount of contaminated water that spills out into our oceans by absorbing rainwater as it falls and then naturally filtering it before it reaches our storm systems. These roofs can also help regulate the temperature inside buildings, which in turn cuts down on heating and cooling costs, both economical and environmental. Green roofs can even help to regulate the temperature in the centres of our cities by absorbing rather than reflecting heat, cutting down on a phenomenon termed the heat island effect. At their best, green roofs can do all of this and provide city folks with local, organic produce. Not bad.

There are two basic types of green roofs: extensive and intensive.

An intensive roof is the type capable of providing food for people, as well as habitat for birds and other winged creatures in need of a place to rest or nest. It typically has between about 8" and up to 15' of soil, depending on the load the roof has been designed to handle (imagine a city in which all new and renovated buildings were required to grow fruits, nuts, vegetables, legumes or grains on their rooftops...) The intensive rooftop is more expensive to design, build, and maintain than its partner, the extensive green roof.

The extensive green roof is the more common and accessible type, and requires far less fuss to design and build. This is the type that we have installed on the studio in our garden.

The elements of the intensive and extensive roof are similar: waterproof layer over roof (we used a product called blueskin), then drainage layer, root barrier, lightweight soil and plantings. The difference is that the extensive green roof has much less soil, anywhere from about 2-6" in depth, and is planted with drought tolerant and low maintenance plants such as sedums and low grasses. The idea here is that once the plants are established, they will require very little care to keep healthy, and will be largely self-sustaining.

When it came to choosing a drainage layer, we stalled out somewhat. There are many different options out there, including gravel, carpet, straw, and thick landscape fabric. We decided to go with a product called dimple-board, or dimple membrane, which is actually a waterproofing product that builders often use around the foundations of houses to prevent water from leaching in. Because the product has dimples in it, these will act like channels so that excess water will drain out to the bottom corner where we will have a rain chain which will empty into a small rain garden. The dimple board comes in rolls at building supply stores for about $100. This was not the least expensive option, but it seemed to us to be the most durable and practical, because we knew that gravel would slip down the sloping roof, and the carpet and straw would break down over time.

Over the dimple board we laid landscape fabric as a root barrier, and then we used bagged organic potting soil as our medium. We considered mixing our own soil, but realized that it would be much less labour-intensive to simply haul the bags up to the roof, and so that's what we did.

The best part was planting the roof. Here is a list of the plants we chose:
-Sedum 'Angelina'
-Sedum 'Summer Glory'
-Sedum 'Murale'

All of these plants are drought tolerant, and, once established, they won't need irrigation to survive unless we are have a very long dry spell, which, given this ridiculously wet spring, seems impossible at the moment).

So, our green roof is planted, but the studio remains unfinished as of yet...another blog, perhaps.