Building a Green Roof – City of Toronto By-Laws

The purpose of the Toronto Green Roof construction Standard is to provide requirements to the design or a green roof construction while meeting the Ontario Building Code requirements. Any Green Roof being constructed in the City of Toronto, Ontario that exceeds 2000 square meters must first fill out a Green Roof Declaration form and submit it to the Municipality of Toronto; you can find the Green Roof Declaration form at the city of Toronto’s website.

The typical components of a green roof required to meet the City of Toronto’s guidelines are as follows starting from your building and moving to the top of the vegetation.

1. First you need a solid structure building that can support the weight and all the components required to meet the City of Toronto By-Law No.583.2009

2. Waterproofing Membrane is similar to those used for conventional roofs, this membrane is a system that resists hydrostatic pressure and also building permit toronto provides protection against water damage.

3. A root barrier is the third layer that is intended to protect the waterproofing materials from possible root penetration in to the waterproofing membrane and the harmful effects that the soil can cause with years of biodegration. Typical materials for the root barrier are sheets of plastic made from PVC, TPO or polyethylene.

4. A drainage system is required above the root barrier to assist in draining off excess water that is not used by the vegetation in your roof. This drainage system can be made from free draining materials such as gravel, or from rigid plastic materials with impressed cups to temporarily store the excess water. The filter fabric is geotextile that helps provide protection against fine soils building up in the drainage paths and ensuring long term efficiency of the drainage layer.

5. Above the drainage system is a moisture retention mat that is used to help store water for the vegetation to absorb over a period of time. This layer is mostly made from recycled fibers stitched to a thermoplastic fabric sheet such as polyethylene and is laid freely on top of the drainage system prior to filling the soil on top. This layer may also serve as a root protection layer.

6. Engineered soil is the next and almost final step, after your soil has been placed on the green roof you need to carefully select the plant species used based on the climate conditions and the maintenance requirements of the plants.

Among a few other steps to consider you also need to ensure the roof you plan on installing meets the proper slop requirements. Minimum slop to ensure proper drainage is approximately 4% slope to the drainage pipes to prevent an excess of water build up on the roof. The roof can have a maximum slope of 11 degrees before you will be required to install anti-shear layers or anchorage and erosion control systems. If your slope is greater than 11 degrees but is less than 22 degrees you will be required to install roofing systems to protect the structure and integrity of the green roofing system. It is not recommended that green roofs be installed with a slope above 22 degrees for safety and structure concerns for the people using the building and walking around the building where possible erosion may fall off the roof.

Installing a green roof can be very beneficial to our environment as the heat that concrete and asphalt store up through the day and release into our environment throughout the night create an unnatural environmental condition that is bad for all plants, animals and humans living in the area. Help prevent some of the effects that humans have had on our environment and the massive structures that we continue to build in our cities by replacing the vegetation your building has disrupted and letting it grow healthy on the roof.

The Toronto Green Roof Construction Standard is the first municipal standard in North America to establish the minimum requirements for the design and construction of roofs. Surly municipalities around North America will follow suit in the future. As of Jan 31, 2010, the Toronto Green Construction Standard applies to all new building permit applications where green roofing is proposed and we recommend that you check with your local municipalities for possible guidelines to the construction of a green roof in your community.

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