Green Roofs

A very common understanding of a traditional green roof is one that supports plant life for environmental, social and/or economic benefits.

What McMaster is doing:

During the 2012 MSU Presidential Election, Siobhan Stewart, MSU President, incorporated the Green Roof Initiative as one of her platform points and received tremendous support from voters. To further develop this initiative, Melanie Fox-Chen, Sustainability student intern, has worked with Siobhan to conduct community consultation on the project. One of the main aspects of her research was the creation of a survey to obtain feedback from the McMaster community about the green roof’s features.
The survey was posted on July 11, 2012 and was continued until September 21, 2012. Key findings from the survey show the following:

- 66.9% of participants would use the green roof for relaxing and would appreciate a calm soothing environment.
- 62.0% would like plants native to Southern Ontario to be incorporated into the green roof.
- 77.8% of participants would like edible plants to be grown on the roof.
- 91.9% of participants would like this area to be non-smoking.

Feedback from the survey has been integrated into the MSU Green Roof Initiative: a report of recommendations.

Another approach to environmentally sustainable roofing is to incorporate a rainwater harvesting system onto building roof tops. The roof of the David Braley Athletic Centre has been constructed with a rainwater harvesting system and uses the captured water to flush toilets within the building. The new Engineering Technology Building also has a rainwater harvesting system that will not only utilize the captured water for grey water purposes, but will also have the capability to treat and utilize the water for potable water uses. To learn more about the project developments, click the link in the left navigation titled "Water" and navigate to the project link.


Benefits of a Green Roof:

Storm Water Runoff: Rainwater that would have normally just run off the roof, into the sewer and then treated at the water treatment plant is mediated by the rooftop vegetation. There is less water overloading the sewage system during periods of heavy rainfall because the rainwater must infiltrate the vegetation before flowing off of the roof. The amount of storm water is decreased due to evaporation and transpiration from soil and plant leaves respectively. The water that does flow into the system is purified because it has been filtered by the soil and not had the opportunity to pick up debris and contaminants that may be on a conventional roof.

Energy Efficiency: The vegetation on a green roof acts like an insulator for the building. In the summer, the vegetation absorbs and uses the sun's rays more than a normal roof which would heat up and transfer the heat into the building. If the building is air conditioned, then the roof also helps to keep the cool air inside the building. During winter months, the extra layer of soil and vegetation on the roof keeps the building heat from escaping as it rises. In short, green roofs result in reduced energy consumption when compared with traditional roofs.

Air Quality: Plants reduce and filter contaminants, such as Greenhouse Gases, in the air. Vegetation also use the heat absorbed for evaporation and transpiration, while a concrete roof just re-radiates the heat into the building and the atmosphere. Together, lower levels of air contamination and air temperature will decrease the level of smog that plagues urban areas on hot summer days.

Waste Reduction: Green roofs last about twice as long as normal roofs because the roof material is not exposed to weathering and the temperature fluctuations are decreased. Having vegetation on the roof means a 50% reduction in the material and costs associated with re-roofing over the building’s life span.

Social Wellbeing: If made accessible, a green roof would directly increase the social health and wellbeing of those who use it and would indirectly benefit everyone by making the planet healthier.


Did You Know...

The most common cause of the pollution of streams, rivers and oceans is surface water running off of yards, city streets, paved lots and farm fields (Higher Education Symposium, Chicago, November 2008).

The British Columbia Institute of Technology describes how there are different types of green roofs:

There are "Extensive" green roofs, which are those that can support between 3” and 6” of light-weight growing medium and become, more or less, self-sufficient in terms of watering and maintenance after one year. These types of green roofs are constructed on large flat roofs and use grasses as a common vegetation choice.

Alternatively, there are "Intensive" green roofs that support 8” to 12” of vegetation but require consistent maintenance. Think of a roof-top garden where there are a variety of potted plants landscaping and the space looks like an at-grade garden parkade.

Finally, there are "Semi-Intensive" green roofs that have aspects of both of the above. These types of roofs harness both the environmental and social benefits of constructing a green roof.


Information above about Green Roofs has been acquired from the British Columbia Institute of Technology. More information can be found on their FAQ page. © British Columbia Institute of Technology


October 10, 2012

News and Events

Interested in learning about green roofs and the living architecture industry? Check out the latest edition Living Architecture Monitor, a quarterly green roof and wall magazine published by Green Roofs for Healthy Cities.