It’s Alive! Unlike a normal roof that most of us tend to forget, a green roof does require regular main- tenance. For an extensive ecological roof, the maintenance is minimised to about six times a year from spring through to autumn. This requires inspection of the roof drains to make sure that they are clear of debris, trimming the plants in spring and periodic weeding. If the roof does not have a built-in irrigation system, even the hardiest of ecological roofs may need additional irrigation during intense summer heat waves. Much of the roof’s maintenance will depend on how the roof is used, the plants that have been chosen and the owner’s gardening habits. Residential green roofs can also be used for recreational gardening. Loft owners in Montréal have also invoked the idea of an urban cottage where the roof may include an outdoor bedroom, shower, summer kitchen and patio surrounded by a roof-top meadow and views of the city. For the building owner, green roofs increase building value and create a personal urban oasis. For the larger community, green roofs reduce the load on a city’s water infrastructure and help to moderate urban temperatures. Clearly, green roofs not only benefit individuals, but they also benefit our neighbourhoods and our cities. The fifth façade has never shown so much potential. D 1 LEED® Canada is an adaptation of the US Green Build- ing Council’s (USGBC) Leadership in Energy and Environ- mental Design Green Building Rating System (LEED®), tailored specifically for Canadian climates, construction practices and regulations. (Source: Canada Green Build- ing Council www.cagbc.org) 2 For more information about urban hanging gardens see: www.rooftopgardens.org 3 More photos of the demonstration project: www.eco- sensual.net/drm/portfolio/projetpilote1.html 4 City of Toronto Green Roof initiative: www.toronto. ca/greenroofs/index.htm 5 Montréal Urban Ecology Centre: www.urbanecology. net CMHC: www.cmhc-schl.gc.ca
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Green Roof Composition The green roof system can be installed once the roof structure has been properly designed and the appropriate roofing membranes have been applied. The system varies from one sup- plier to another, but usually contains a number of items such as an anti-root membrane, water drainage panels, a geotextile and specially for- mulated green roof light earth substrate. The weight of the earth holds the system in place by gravity. Now the gardening begins! The most ap- propriate categories of plants for extensive green roofs are wild grasses, wild meadow flowers and sedums (waxy plants). The eco- logical goal is to favour indigenous plants, but the final choice depends on the chosen green roof technology and the roof’s planned use.
A number of institutional extensive projects in Montréal have used clover for its low-cost and tenacious character. 5 Each green roof supplier is capable of furnishing informa- tion about the appropriate choice of plants and their aesthetic impacts. The installation of an irrigation system also depends on the type of roof and choice of plants. The more ecologically-oriented the roof, the less likely that it will need an irrigation system. In cit- ies, irrigation of green roofs and gardens uses municipal water. Rain and/or grey water recu- peration and indigenous landscaping strate- gies can help reduce summertime demand for city water resources.
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