ECO: Green roof benefits

When you're watching coverage of the 2010 Olympic & Paralympic Games, take a look at the roofs of the Olympic Village. They're green, and I think they represent exactly the kind of design we need to be incorporating in all developments, especially large ones in urban areas.

After the games are over, the Olympic Village will be an urban centre, including residential, retail, commercial and public space, and it was built sustainably. They've incorporated many methods for conserving water and energy, including ground-source heating, heat transfer from sewer lines and stormwater management using swales planted with native vegetation. The most visible are the green roofs.

The designers of the Millennium Water development were required by the City of Vancouver to make sure the total roof area was at least 50% green. That adds up to almost 300,000 square feet of green roofs in this project alone. That's a bold move on the city's part, and one I think should be required everywhere.

Recently, Toronto became the first city in North America to adopt a bylaw that requires and governs the inclusion of green roofs in new development. That applies to new residential, commercial and industrial building permits over a certain size. That's really a step in the right direction.

Green in more ways than one

A green roof is the perfect roof. They are "green" and can save you money on your heating and cooling bills. They clean the air, produce oxygen and native habitats for wildlife. They can also provide additional living area for your home, which allows you to reduce the footprint but still have more space.

The roof system at Millennium Water is an extensive "blanket" type of system developed over the past 40 years in Germany by Xero Flor. It incorporates the vegetation, water-retaining fleece, drainage barrier and root barrier in one. The plants are grown in fields, then rolled up and transported to the rooftop and installed. It's a lightweight system that can be used in many homes.

The roofs are planted with a mixture of sedum and drought-resistant succulents that flower in the summer and go dormant in winter. They are tough. They tolerate extremes - they can take the heat of summer and cold of winter - and they don't need irrigation once they are established.

Stormwater Runoff

A green roof retains stormwater and decreases the rate of runoff; it slows the water as it percolates first through the green roof before it goes to the drain.

The roof also stores water in the plants, then releases the moisture slowly back into the atmosphere. Any excess water that does run off the green roof has been filtered naturally by the plants.

Reduce Waste

A green roof will outlast traditional roofs by decades. Since the actual roof membrane is shielded from the sun's UV rays, and protected from wind, temperature extremes and the thermal stress of a freeze-thaw cycle, it will last longer. That means all the cost of re-roofing (consumer cost, cost to the environment to create new roofing materials, and the cost to dump the old roof into a landfill) are reduced.

Urban Heat Island

The temperature in a city can be 10 or 20 degrees higher than the temperature around it - that's the "heat island." The building materials such as concrete and asphalt shingles absorb solar radiation and then re-emit it. Green roofs absorb that same solar energy and use it to grow the plants. That process also cools the air through evaporation. On a hot summer day, the temperature of a green roof can be cooler than the air temperature. (On a traditional asphalt roof, the surface temperature is usually many degrees hotter than the ambient air temperature. Go figure.)

Reduce heating/cooling costs

Green roofs insulate buildings, essentially by shading the roof surface and by preventing heat from moving inside. That keeps the interior temperature cooler. It also keeps the roof surface temperature more constant - it doesn't get extremely hot or extremely cold. That takes a strain off the heating and cooling system, and saves money.

More than just good looks

A green roof provides an oasis for wildlife - birds and insects can live on it. And I think green roofs just simply look good. While you're watching the athletes compete for medals, be sure to check out the red patterns of Olympic athletes playing hockey, curling and snowboarding.

("Olympic Village gets gold for roofs" prepared by Mike Holmes/National Post)