Measures to reduce the urban heat island effect in Rosemont–La Petite-Patrie

Rosemont – La Petite-Patrie (137,000 residents) is a densely built borough located in the centre of Montreal. The urban heat island (UHI) effect—a phenomenon whereby the temperature in an urban area is higher than in surrounding areas—is very pronounced in many parts of Rosemont – La Petite-Patrie. Climate change should increase the annual number of extreme heat days in Montreal. In April 2011, the Rosemont – La Petite-Patrie borough council revised its zoning bylaw to include four new regulatory measures aimed at addressing UHIs. The new system of regulations and permits provides an opportunity to educate the public and developers about the impact of UHIs on human health and energy consumption and to effectively apply the new regulatory measure. Although climate change was not a determining factor, the measures contribute to strengthening the resilience to climate change. While it is too late to measure the effect of Rosemont’s new zoning bylaw on the reduction of UHIs locally, the number of roofing permits issued to date is a good indicator of the impact of the new zoning bylaw. It shows that the regulations, along with a series of other policies, programs and tools, can be effectively used to strengthen resilience to climate change.

Understanding and Assessing Impacts

Literature review, consideration of the impact of heat islands on vulnerable populations. Consideration of long-term climate forecasts. During the summer, sectors of downtown Montreal recorded temperatures of up to 12 ºC higher than those recorded in surrounding rural areas. According to the forecasts, climate change is expected to result in an increase in the annual number of hot days in Montreal.

Identifying Actions

Option of imposing regulatory measures to address heat islands. The Rosemont borough council is also setting an example by installing reflective roofs on municipal buildings.


  • Extend vegetation cover by planting trees, shrubs and climbing plants, which will create new open spaces, and by installing green roofs.
  • Increase the reflectivity of building surfaces and surface materials by installing reflective roofs; using light-coloured surface materials for paving roads, sidewalks, parking lots and driveways; and adopting municipal planning and development measures that take climate into account.
  • Reduce residual heat by renovating buildings and improving public services to promote increased energy efficiency, installing equipment, and adopting anti-idling bylaws.


Option of implementing a zoning bylaw to control rehabilitation of infrastructure and bring about the installation of green infrastructure, reflective roofs. The borough of Rosemont–La Petite-Patrie is one of the first communities in Canada to have imposed, by bylaw, the installation of reflective roofs.
In April 2011, the Rosemont–La Petite-Patrie borough council undertook a complete revision of its zoning bylaw to include the four following regulatory measures to combat urban heat islands:

  • In the event of a complete roof replacement or new building construction, the building owner is required to install either a green roof (with vegetation), a white roof or a roof with a highly reflective coating or may use a combination of the three options. The material must have a minimum solar reflectance index rating of 78, certified by the manufacturer’s specifications.
  • At least 15% of the area of any new parking lot having 10 or more parking spaces must be open area landscaped with plants, shrubs and trees.
  • Road surfacing materials used for any new parking lot or any new loading or storage area must have a minimum solar reflectance index rating of 29.
  • At least 20% of the area of a lot on which a new building will be built must be open area landscaped with plants, trees or shrubs. This provision does not apply to main commercial arteries.

Outcomes and Monitoring Progress

Although it is difficult to assess the impact of the borough of Rosemont’s new zoning bylaw on the reduction of urban heat islands at the local scale, the number of roof transformation permits issued to date is a good indicator of the impact of the new bylaw. It shows that the bylaw, in conjunction with a series of other policies, programs and tools, can be used to strengthen the borough’s climate change resilience.

Next Steps

This model could be replicated in other Montreal neighbourhoods.