blue roofs the fifth façade — beautiful affordable eco-roofs
building technology | up on the roof by owen rose
roof gardens structure
eco-technology water retention Montréal
Whether we call them vegetated roofs, roof gardens or ecological roofs, there are three main categories of green roofs . The best known is the rooftop terrace with flower boxes. Poetically referred to as hanging gardens , they apply equally to roof and balcony installations. 2 The next category is intensive green roofs with a layer of earth (growing substrate anywhere from 30cm to 2m thick) and plants, even trees, over most of their sur- face. Without knowing it, you have prob- ably already seen them over car parks and projects such as the Robson Square Centre in Vancouver and the central plaza of Place Ville-Marie in Montréal. The structure of these roofs has to be strong enough to take the weight of a waterlogged snow- covered garden that can be tremendously heavy. Over the past number of years, new lighter green roof technologies have contributed to the third category: extensive , eco- logical or ecoroofs. Much lighter than the intensive roof, the substrate ranges from as little as 5 to 15cm in depth. The advent of extensive roofs is now why we are able to promote green roofs for most types of construction. Their lightness makes them much more economically viable given their reduced structural requirements. roofs offer natural cooling, a greater lifespan and better rain water management. They re- tain about 50% of fallen rain (returning water to the atmosphere bypassing the city’s sewer system). The other 50% will still find its way to the drain, but the return of this water is de- layed, which helps city infrastructure manage water levels during downpours and intense rainfall.
1
The human body is largely composed of water and its intimate connection to the blue planet does not stop with the flush of a toilet. Often a source of grief: too much or not enough, water is both a visible and invisible concern for cities. Not only do we have to find a source, clean it up for potable use and then distribute it, but we also have to dispose of it. Black or grey, waste water treatment is a cost- ly and difficult task. Think of cities such as Halifax and Victoria that dump their untreated wastewater directly into the ocean. Although Montréal has a large sewage treatment plant at the east end of the island, the city still aver- ages about 22 discharges of untreated sewage directly into the Saint Lawrence River each year. When it rains too much the combined storm and sewer system cannot process all of the water from our houses, hospitals, facto-
ries, rooftops, and polluted streets. Thus the problem is passed on to the fishes, whales, and other cities downstream. Now that we have started to face the grow- ing threat of environmental problems such as urban heat islands, air, water and noise pollution as well changing weather patterns, ecological building criteria such as the LEED 1 (Leadership in Energy and Environmental De- sign) green building rating system have en- couraged the construction and design of more ecologically sustainable buildings. In the six LEED categories, water management takes on several forms: one is a vegetated roof. Instead of installing deserts of tar and grav- el on our roofs, more and more institutions, businesses and homeowners are opting to grow fields, gardens and vegetable patches on them. Aside from their obvious beauty, green
on site review 17
58
Made with FlippingBook interactive PDF creator