Rainwater Management in Quebec

As urbanization expands, stormwater management has become a critical issue. The increasing impermeability of surfaces—due to asphalt, concrete, and rooftops—prevents rainwater from naturally infiltrating the ground, significantly raising the risk of urban flooding.

Implementing effective retention and controlled drainage solutions helps mitigate these risks while ensuring compliance with local regulations, particularly in Quebec.

Rainwater Management in Quebec

Quebec’s legislative framework already establishes specific requirements for stormwater retention and drainage. In Montreal, Regulation 20-030 governs stormwater infrastructure, especially for projects exceeding 1,000 m² of impermeable surfaces. Future amendments may further promote rooftop water retention.

Current Regulatory Obligations

• A stormwater retention permit is required for certain buildings (commercial, industrial, and institutional).
• Drainage flow rates must adhere to maximum thresholds based on the drainage zone.
• The use of flow control devices is encouraged to reduce the strain on municipal infrastructure.

Infrastructure Standards

• Stormwater retention systems must be designed by a certified engineer, ensuring compliance with regulatory standards.
• Materials and drainage system dimensions must meet specific technical requirements to ensure seamless integration with existing municipal networks.

How Impermeable Surfaces Contribute to Urban Flooding

Urban expansion gradually replaces natural, permeable surfaces with impermeable structures like roads, buildings, and parking lots. This transformation disrupts natural water absorption, leading to:

• Increased urban runoff, overloading sewer systems.
• Higher peak water flow rates, causing sudden flooding.
• Degraded water quality, as pollutants from urban surfaces are carried directly into watercourses.

Stormwater Retention and Drainage Solutions

To improve stormwater management and reduce urban flooding risks, different strategies can be implemented.

1. Stormwater Retention

Retention techniques temporarily store water before gradually releasing it into the sewer system or ground. This method helps reduce peak water discharge and prevents sewer system overloads.

Common Retention Solutions

• Retention basins: Dedicated areas designed to collect and hold excess water before controlled drainage.
• Green roofs: These absorb rainwater, slowing runoff and reducing the impact of heavy precipitation.
• Underground reservoirs: Storage systems that capture and retain stormwater for later reuse or slow release.

2. Controlled Stormwater Drainage

Regulated drainage prevents sudden sewer overloads and minimizes flood risks. Specific stormwater control infrastructure ensures gradual and safe water evacuation.

Controlled Flow Roof Drains

Also known as roof inlets, these systems regulate the speed of water drainage, reducing stress on municipal networks. By allowing temporary water accumulation on the roof, these drains prevent sewer overload during heavy rainfall.

This technology is particularly effective for large industrial and commercial roofs, where rapid water runoff could overwhelm storm drainage systems.

Challenges and Risks of Rooftop Water Retention

While rooftop water retention offers a promising solution, improper implementation can lead to structural issues. Excessive water accumulation may:

• Compromise roof integrity, increasing the risk of leaks and water infiltration.
• Accelerate material degradation, reducing the lifespan of roofing membranes and structures.

Before adopting rooftop water retention solutions, it’s crucial to assess the structural capacity of the roof to handle additional water loads.

Expert Consultation for Optimized Stormwater Management

For a thorough evaluation of your roof and tailored stormwater management recommendations, contact our team today. Our experts ensure durable and high-performance solutions suited to your building’s needs!