With growing environmental awareness and the need to rethink the way we build in urban areas, green roofs are emerging as an innovative, environmentally-friendly solution.

Also known as living roofs or vegetated roofs, these features offer remarkable ecological and economic benefits, harmoniously blending nature and urbanity.

In this article, our Montreal roofers present the different types of green roofs, explain the advantages they offer and outline how to maintain them.

What is a green roof?

Green roofs, also known as vegetated roofs or living roofs, are innovative architectural solutions that combine urban construction with natural vegetation.

Unlike traditional roofs that are covered in membrane or gravel, green roofs are covered, in whole or in part, with living plant vegetation. This garden-like cover transforms a roof into an oasis of green with remarkable environmental, economic and aesthetic benefits.

Types of green roofs

Green roofs fall into several categories, each adapted to specific objectives and varied contexts. The three main types of green roof are:

  • Extensive green roofs: These are characterized by a relatively thin layer of vegetation and hardy, low-maintenance plants. Typical species include grasses, mosses and succulents. Extensive green roofs are lighter and require less water and maintenance, making them suitable for larger buildings.
  • Intensive green roofs: Intensive green roofs feature a wider diversity of plants, including trees, shrubs and even entire vegetable gardens. This variant obviously requires more maintenance and a more robust support structure due to the increased weight of the vegetation and substrate.
  • Semi-intensive green roofs: These combine features of both extensive and intensive green roofs. They offer a greater variety of plants than extensive roofs, but require less maintenance than intensive roofs.

To find out which solutions are best suited to your building, contact our roofers today!

The components of a green roof

The structure of a green roof is made up of several interdependent components that work together to create a thriving ecosystem.

  • Substrate: The substrate is the artificial soil placed on the roof to support plant growth. It provides nutrients to the chosen plant species while draining water properly.
  • Plants: The species of plants you choose for a green roof depend on the type of roof and local environmental conditions. Roof plants must be able to thrive in specific rooftop conditions, which usually involve exposure to sun and wind, and significant temperature variations.
  • Drainage system: Green roofs require an effective drainage system to eliminate excess water and prevent stagnation. Proper drainage ensures that the substrate remains well aerated and that plants receive the right amount of water.

Green roof regulations in Quebec

In Quebec, green roofs represent a promising solution to mitigate the environmental issues associated with urbanization. However, the regulations governing these green installations are still under development. Here’s an overview of current legislation and the role played by the Régie du bâtiment du Québec (RBQ) in regulating green roofs.

The role of the Régie du bâtiment du Québec (RBQ) in regulating green roofs

Although roof construction legislation is not specific to green roofs, the Building Act and the RBQ Standard Guide for Selection, Installation, and Maintenance of Plants for Green Roof Systems provide guidance to ensure the safety and viability of these environmentally-friendly features.

Technical criteria and standards for green roof construction

The RBQ’s technical criteria are designed to ensure that green roofs are safe, functional and durable. These include ethe following:

  • Fire safety: Since vegetation is flammable, builders have to take measures to minimize the risk of fire and facilitate access for firefighters.
  • Load-bearing capacity: Green roofs impose an additional load on the building structure. The RBQ has established maximum permissible loads to prevent any risk of overloading.
  • Waterproofing and drainage: Builders must include provisions to prevent water infiltration and stagnation, which could damage the roof structure.
  • Maintenance: The technical guide includes recommendations for the regular monitoring and maintenance of green roofs, to verify that they are functioning efficiently.

What are the benefits of green roofs?

Although installing a green roof generally costs more than installing a traditional roof, even though you could be eligible for a green roof tax credit, there are many benefits to offset these costs.

Better rainwater management

Green roofs absorb almost 80% of rainwater in their soil. This water is later soaked up by the plants, eliminated slowly through the drainage layer, or it evaporates.

This process delays the flow of rainwater into the storm sewer system, which helps to stabilize groundwater levels, decreasing the peak load on the sewer system and reducing the risk of flooding. It also purifies the rainwater by removing various pollutants.

Increased biodiversity

The plants on a vegetated roof can provide an ideal habitat for various species of birds, butterflies and insects, which is particularly helpful in urban areas that are mostly made up of concrete and asphalt.

Improved air quality

Green roofs can combat air pollution, since plants filter the harmful airborne particles and gases emitted by cars and factories.

Mitigating the heat island effect

Green roofs reflect more sunlight and absorb less heat than traditional roofing materials. A living roof can help cool down urban areas in summer.

Reducing ambient noise, outside and inside the building

Vegetation provides excellent acoustic insulation for flat roofs, because it absorbs sound waves. It has been proven that a 12 cm thick layer of vegetation can reduce airborne sound by almost 40 dB.

So, a green roof can act as an acoustic barrier for your building by absorbing sound. This means it can help you provide a quieter environment both inside and outside your building.

More leisure space

A green roof provides additional space that can be used to create a vegetable garden or a terrace, or simply kept as a pleasant natural environment.

With access to a new open-air space that can be used for meetings or relaxation, your employees will be happier at work.

More energy efficient

Increasing the R-value (a measure of a material’s resistance to heat flow) of the roofing system and lowering the roof temperature reduces the building’s heating, ventilation and air conditioning needs, resulting in significant energy savings.

This also affects the lifespan of heating and air conditioning systems, because they will undergo less strain.

Over its estimated 40-year lifespan (another benefit), a green roof could help you save on a numerous expenses. Of course, the benefits of each green roof depend on design, geographic location, environment and the building itself.

Certified roofers are the best people to tell you what you really need!

Increased property value

A living roof can also increase property value, particularly in urban areas where green space is scarce.

With its 40-year lifespan, a green roof is an excellent selling point, because the future owner will probably not need to do any commercial roof repairs for a long time! Living roofs last longer because the plants protect the flat roof membrane from UV rays and extreme heat.

How to maintain a green roof

Maintaining a green roof is essential to ensure that it lasts a long time, functions efficiently and looks good. While offering many advantages, these types of roofs do require special attention according to the types of plants chosen and the season.

Maintenance according to the type of vegetation

Green roofs are home to a variety of plants, each with their own growing requirements. Before selecting plants for your roof, assess the amount of maintenance you’re prepared to do. Mosses and succulents are among the least demanding species, while a vegetable or flower garden will require more regular effort.

Watering frequency according to plant type

Watering frequency depends on the type of plants on your green roof. Some plants, like orpine, are drought-resistant and can survive without frequent watering. Others, like vegetables and flowers, will definitely require regular watering.

Pest management

Just like traditional gardens, green roofs can be vulnerable to pests and parasites. Grubs, insects and birds can damage vegetation. If you notice any signs of infestation, you’ll need to consult a landscaping professional who can identify the problem and implement appropriate prevention or treatment measures.

Protecting your green roof in winter

To ensure that your green roof lasts through the winter, choose plants adapted to your region’s climate (especially in Quebec). Cold-hardy species require less care when preparing for the winter season. You can be confident that your roof is designed to withstand winter conditions by following the recommendations of a professional.

Duro-Toit can answer your questions about green roofs

There is no sign that green roof popularity is going to diminish anytime soon. Living roofs offer so many advantages for commercial and residential buildings that they will continue to find a place in big cities like Montreal.

If you are interested in installing a green roof on your property, contact us today! Duro-Toit can help you throughout the process, via services like professional roof inspection to confirm that your building can accommodate a vegetated roof.

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