Urban heat islands

Summer in Quebec can be stifling, especially in the city. Some neighborhoods become real heat traps, much hotter than surrounding rural areas. This phenomenon has a name: urban heat islands.

Fortunately, there are concrete solutions to combat it. In this article, we’ll explain the causes, impacts, and how your roof can help cool the city.

What is an urban heat island?

An urban heat island (UHI) is a densely built-up area where the temperature is significantly higher than in nearby rural zones. This effect is caused by materials that retain heat (asphalt, concrete, dark roofs), limited vegetation, and poor air circulation.

In Montreal, this phenomenon is especially pronounced during summer heatwaves, increasing health risks, particularly for the elderly and children. As roofers, we play a key role in mitigating these effects through more sustainable, reflective roofing choices.

What causes heat islands?

Urban heat islands are the result of a combination of urbanization factors:

Surface mineralization: Materials like asphalt, concrete, and dark roofing absorb and store solar heat throughout the day.
Lack of vegetation: Trees and green spaces, which naturally cool the air, are often missing in densely built neighborhoods.
Building density: Vertical surfaces and the “urban canyon” effect reduce air flow and trap heat.
Human activity: Air conditioning, vehicles, and industrial operations generate heat and intensify the problem.

These factors create an unfavorable urban microclimate where temperatures can rise 5 to 10 °C higher than in nearby rural areas.

Impacts of urban heat islands

The effects of heat islands go far beyond simple discomfort.

Health risks

Seniors, children, and people with chronic illnesses are especially vulnerable during heatwaves. UHIs can cause heat strokes, worsen respiratory diseases, and increase mortality.

Energy overconsumption

The hotter it gets, the more buildings need cooling. This leads to massive air conditioning use, driving up electricity demand and energy costs.

Decline in quality of life

Living in a heat island zone means enduring stifling nights, empty public spaces, and a general feeling of discomfort. It affects neighborhood appeal and residents’ mental well-being.

Environmental impact

The energy consumption linked to UHIs contributes to greenhouse gas emissions. A vicious cycle continues: the hotter it gets, the more energy we use, further accelerating climate change.

Available solutions

Luckily, several solutions can slow the development of heat islands and make cities more breathable.

Green urban spaces

Planting trees, creating parks, or greening alleyways can significantly reduce ambient temperatures. Plants naturally cool the air through evapotranspiration and provide shade to create cool zones.

Reworking surfaces

Replacing asphalt surfaces with permeable or light-colored materials (e.g., light paving stones, reflective slabs) helps reduce heat absorption.

Bringing water into the city

Fountains, ponds, or blue corridors help naturally cool the environment and make public spaces more pleasant during heatwaves.

Raising awareness and planning

Municipalities, developers, and residents all benefit from integrating UHI mitigation in urban planning. Mapping affected zones, designing green corridors, or updating construction standards are key actions.

Roofs: a concrete and accessible solution

The roof represents 20% to 25% of a building’s visible surface in urban areas. It absorbs a massive amount of heat when covered with dark materials like traditional asphalt shingles.

That heat is then transferred inside the building, increasing the need for air conditioning and warming the outdoor environment. Fortunately, there are effective ways to significantly reduce this effect.

White roofs

Made with reflective membranes or white coatings, white roofs reflect sunlight instead of absorbing it. This is ideal for flat or low-slope roofs and can lower surface temperatures by 20 to 30 °C.

Green roofs

Covered with substrate and vegetation, green roofs act as cooling islands. They filter air, reduce heat islands, retain rainwater, and extend the roof’s lifespan.

Reflective shingles

For sloped roofs, light-colored or reflective granule shingles help reduce heat buildup. This is an affordable solution that fits many types of homes.

And what about insulation?

Not visible but just as important, roof insulation keeps cool air in during summer and warm air in during winter. Combined with a high-performance roof, it boosts comfort and reduces reliance on air conditioning.

How to choose the right solution?

The right choice depends on several factors:

Building type: Single-family home, duplex, rental property, or commercial building.
Roof slope: Some materials are not suitable for sloped roofs.
Budget: Green roofs require a larger initial investment but offer long-term savings.
Environmental priorities: Greening goals, municipal grant eligibility, or LEED certification.

At Les Couvreurs Duro-Toit, we offer full support to help you choose and install the best solution for your property, based on technical requirements and long-term goals.

Grants available for real impact

White roofs are increasingly promoted by municipalities as an effective way to combat urban heat islands. Beyond their environmental benefits, they give homeowners access to real financial incentives.

In Montreal, the RénoPlex program offers a grant of $50 per square meter for roof renovations using white membranes. This initiative aims to support energy-efficient upgrades while reducing the impact of extreme heat in dense neighborhoods.

To qualify, applications must usually be submitted before starting the work and must involve a certified contractor. At Duro-Toit, we guide you every step of the way—from choosing materials to securing your roofing subsidy.