Published on June 23rd, 2008 | by Stephanie Evans
Biodiverse Green Roofs
Green roofs are vegetated roof covers constructed on top of a roof deck. Sometimes called an ecoroof or sky garden, this burgeoning technique is the ultimate in green home and building design.
It gives users the opportunity to reduce their impact on the planet while simultaneously contributing to healing damaged urban ecosystems. Green roofs cover impervious roof surfaces with living, breathing, permeable plant material.
How it Works
Green roofs, which are living roofs made up of plants and grasses, are part of sustainable construction in most major cities and in many parts of Europe. A true green roof system reduces heating inside the home or building by up to 30–40 percent, making it a natural air conditioner.
In the winter months, soil and layers of other material significantly increase the insulation levels in the roof, reducing heat loss and keeping the home warmer. Additionally, installing a green roof adds to the health and beauty of the natural environment and replaces soil that is displaced during construction.
A green roof is built somewhat like an open-face sandwich:
- It typically starts with a layer of rigid roofing insulation
- Next, an impervious layer (such as EPDM rubber) impregnated with a rooting-resistant chemical is added
- This foundation is followed by a layer of loose drainage material (such as crushed pumice or gravel, a filter fabric that keeps the layers separate but still allows water to pass through, a scientifically-formulated planting medium, and finally, the plants themselves
These roofs are made to be extremely long-lasting, and have a good track record for reliability in Europe, where they have been in use since the 1970’s. While green roofs may be great, the practicality of this feature must be examined on a case by case basis.
Many homes do not have the structural means to support a living roof, or their local zoning laws may not permit such a project. Homeowners in these circumstances don’t have to give up their efforts for a sustainable home. Products like reflective roof coating can help by reflecting more of the sun’s energy back into the atmosphere, keeping the home cooler and reducing air conditioning bills.
Application in Urban Settings
There are two basic types: “extensive” and “intensive”. The extensive green roof is a self-sustaining biotic community, colonizing the exposed, dry, and shallow-soil environment of a roof. They are seeded with alpines, succulents, herbs, and grasses appropriate to the climate, and are left nearly alone to develop naturally. They are not usually accessible for use.
The intensive green roof is a more involved and expensive affair with deeper soil that can accommodate larger plants, even trees. They are designed for recreation, and differ from roof gardens in that the whole surface of the roof is covered with soil and plantings, as opposed to many containers with plants.
Green roofs have become increasingly popular, especially in commercial urban architecture, because they ameliorate loss of greenspace, absorb carbon dioxide, reduce building heat gain, and recreate natural habitat.
They are particularly remarkable in their ability to filter and control stormwater runoff: green roofs can absorb anywhere from 50 to 95 percent of the rainwater that falls on them.
Greenroofs offer one big piece of the solution to Urban Heat Island syndrome. Modern cities, with their huge production of waste heat, and replacement of cooling, sun-reflecting vegetation with heat-absorbing asphalt and concrete, are hot spots on the planet’s surface that create their own unnatural weather.
Perhaps one day our city roofs viewed from the air won’t look like geometric scars on the landscape, but waved patterns of waving greenery…