A green roof for a healthy city

Toronto has picked up on a green idea that the Europeans have been using for the past two decades; rooftop gardens of bergenia, blazing star, coneflowers, white lambs' ears, lavender, and other low-maintenance grasses, mosses or succulents. The idea is spreading as city and federal environment departments and a private coalition called Green Roofs for Healthy Cities spread the word about the benefits.

Green roofs absorb storm water, slowing the runoff into city sewers that carries dog waste, road oil, roof tar and lawn chemicals into lakes and rivers.

They insulate buildings, moderating hot and cold temperatures and reducing energy use.

They release oxygen into the atmosphere, countering excess carbon dioxide levels from industrial and auto emissions and helping to reduce the "heat-island effect." That effect is the roughly eight-degree difference between the temperature of a city and that of the surrounding countryside, and it promotes smog.

They also extend the life-span of a roof to 30 years from 15.

Environment Canada has calculated that greening 6 per cent of Toronto's rooftops would yield huge environmental and economic benefits for the city; an annual, direct reduction in air pollutants of 30 tonnes, a 5- to 10-per-cent decrease in smog-alert days each year, a drop in greenhouse-gas emissions of 2.18 million tonnes a year, annual energy-cost savings of $1-million, a reduction of the urban heat-island effect of 1 to 2 degrees.

Green roofs are the best of both worlds; they benefit the environment and they save money too. It's time to give this ideawider use.