You may have heard about (or caught a glimpse of) green roofs in urban areas of Ontario.  Especially in Toronto, as it is the first city in North America to enact a bylaw requiring green roofs on all new developments.


Whether a development is commercial, institutional, residential or industrial, if it has a roof that is at least 2,000m2, you are required to build a green roof.

It’s not totally cut and dried.

Let’s face it.  Municipal bylaws rarely are.  So, if you’re wondering whether or not you are mandated to build a green roof, you can use this Green Roof Bylaw Screening Form (provided by the City of Toronto/City Planning Department) to find out.

If you are required to build a green roof, you are definitely going to want to find out the best practices of building green roof structures.  Lucky for you, we’ve compiled a great little summary of everything you need to know about green roofs to help you.

What is a green roof?

It’s pretty simple, really.

A green roof is an extension of your current roof allowing for growth of vegetation out of some sort of medium.  You will need:

  • A root repellent system
  • A drainage system
  • A filtering layer
  • A growing medium, and yes, you guessed correctly . . .
  • Plants

Why build a green roof?

Aside from potentially being a legal requirement, green roofs also provide a range of benefits to building owners AND the general public.

The benefit to the public is, first and foremost, that of improved air quality – an ongoing concern in any major urban area.  Plants on green roofs can capture airborne pollutants, acting as a filter while reducing the amount of CO2 emissions released into the atmosphere.  Green roofs aid in city storm water and waste management, as well as creating a more aesthetically appealing environment for all to enjoy.

Green roof structures can also dramatically reduce building costs – in more than a few ways.

How?  By reducing the amount of energy needed to heat or cool your building.  In fact, research published by the National Research Council of Canada found an extensive green roof reduced daily energy demand in the summer by over 75%.


Get the report!  Performance Evaluation of an Extensive Green Roof – National Research Council Canada

Check out your potential savings

This handy tool, the Green Roof Energy Calculator (courtesy of Portland State University), allows you to compare the annual energy performance of a building with a conventional (or highly reflective) roof to the same building with a vegetative green roof.

The good news is that green roofs are also durable, fire retardant and noise reducing.

Explore your options

Now that you’ve investigated the bylaw requirements and benefits, you’ll need to know what your building options are.

A Complete Green Roof System

As the name suggests, a complete green roof system means every aspect of the roof is designed to support plant growth.  Certainly the most complex option, a complete system also provides to most flexibility when it comes to drainage, growth medium and the type of plants you choose to grow.

Modulated Green Roof Systems

A much less complex option, a modulated green roof involves covering the whole roof with trays of plants growing in some type of medium.  Obviously, this option is significantly more limiting, especially in terms of the variety of plants that can be grown.  The installation is, however, quite a bit simpler.

Pre-cultivated Green Roof Systems

A pre-cultivated green roof means your plant life is grown on interlocking vegetation blankets that are then transported and placed on your roof surface.  Using vegetation blankets will provide immediately mature plant life (as the blankets are pre-planted and grown to maturity elsewhere) but this is the most limited option in terms of plant varieties.

The Conclusion

Overall, green roofs are a terrific choice.  Whether you’ve been legislated to incorporate a green roof into your building structure or not, green roofs generate savings for building owners and the municipality.  And, they can be pretty nice to look at!

Wouldn’t you like to take a stroll down a garden path, up on your roof?