4 things you should know about green rooftops

Posted on November 16, 2015

We’ve spoken before about how more than half of the world’s population will live in cities by 2050.

Canada is leading this charge with 81 per cent of the country already living in urban centres.

With high population density comes a higher concentrated use of concrete, cement and aggregates. And with those, comes higher risk of urban heat island effect and stormwater run-off from impervious surfaces that don’t absorb water, but do absorb heat.

Lafarge Canada has a number of pervious and eco-friendly concrete solutions to help mitigate these risks. This should help our country achieve its increasing call for green roofs and continue to lead in sustainable urbanization in North America.

So what are green roofs?

Green roofs are areas of a roof, either flat or sloped, that have the ability to grow vegetation. There are a number of different types of green roofs and they consist of some or all of the following components:

  • Vegetation
  • A planting medium (often soil-less)
  • A filter layer
  • A drainage layer
  • A moisture retention layer
  • A waterproof root barrier layer
  • A separation layer
  • A thermal barrier
  • A vapour control layer
  • A structural deck made from concrete

How do green roofs help build better cities?

A green roof absorbs rainwater and returns it to the atmosphere. It also contributes to a reduction in stormwater runoff during the rainier months. These are only a few of the benefits that green roofs can add to your city—including a major ease on urban heat island effect and added wildlife habitats and recreational spaces that they provide. Some communities are even forming around a few successful movements to create urban farms as green roofs—which in turn provide produce to local restaurants, grocers, and underprivileged neighbourhoods. 

These are some of the reasons that they add LEED credits to your building.

This contribution to a low energy footprint in your projects adds to the structural integrity of the building’s you are providing to a city. Green roofs cut down the amount of heating and air-conditioning escaping from your buildings during the summer and winter months. It also extends the lifespan of your roofs due to its ability to regulate rooftop temperatures—fewer repairs and replacements mean less time spent navigating through busy city streets with construction supplies.

Different types of green roofs

There are two types of green roofs, each of which can sustain different types of vegetation:

Extensive green roofs range from between 5 to 15 centimetres deep in their growing media layer. They’re great for easy installation and low maintenance, as they require drought-resistant plant species that can survive harsh winds and elevated surfaces. These are generally not used for recreational spaces and can span very wide areas, without a lot of effort.

Intensive green roofs involve deeper planting media, irrigation systems, landscaping features and a broader range of plant species. This type of rooftop gives architects the opportunity to include more high-maintenance plants, trees, shrubs and decorative features into their designs. These types of roofs have also been converted into urban rooftop farms.

What legislation is there in Canada around green roofs?

Toronto lead and is leading the North American green roof movement with their implementation of City bylaws on April 30, 2012. They are the first metropolitan city on the continent to do this. The City requires green roofing on all newly built developments with a minimum gross floor area of 2000 square metres. The City has seen less than 5 per cent variance on following the bylaw since its implementation—Toronto issued 123 permits by early 2015.

Though other cities have yet to put this into their legislation, many provincial organizations, such as these ones in Nova Scotia and Quebec, are coming out with green roof manuals to help builders and architects work together towards our sustainable-building feature.

Categories: Lafarge Blog