Smart Blue Roofs: Turning Rooftops into Active Stormwater Infrastructure

Urban Stormwater Management in Practice

Climate change is expected to increase the intensity and frequency of heavy rainfall, raising the risk of urban flooding in Ontario. In 2024, the City of Mississauga, Ontario, experienced two severe storms. The first event on July 16 generated up to 102 mm, and another large storm on August 17–18 produced 110 mm, as measured at a rain gauge on Britannia Road. These events resulted in flooded roadways and overflow from a nearby stormwater pond at Matheson Blvd. East and Hurontario Street. These events raised questions about how existing stormwater systems perform during extreme rainfall, reflecting the importance of flood-resistant drainage infrastructure across the region to lower damage to public and private property.

Conventional flood-management strategies often rely on expanding detention facilities or replacing undersized sewers for additional storage and conveyance. These interventions involve substantial capital costs and construction, making it essential to explore alternative stormwater-management approaches. Distributed measures such as low-impact development (LID) can provide additional runoff-control capacity alongside conventional detention ponds. However, many ground-level LID practices require land, excavation, and integration with existing surface drainage.

In commercial and industrial areas, large rooftops occupy a significant portion of the built-up area. Integrated roof runoff management can reduce peak inflows and, under appropriate design and adoption conditions, may reduce required downstream storage or defer sewer upgrades. In this context, rooftops can be viewed not only as drainage surfaces but also as valuable assets within the urban water system. Green roofs are an established rooftop stormwater-management approach, but their implementation requires vegetation, growing media, structural loading, and ongoing maintenance considerations. Alongside green roofs, blue roofs provide another rooftop runoff-management option, particularly where controllable detention and retention are desired.

From Blue Roofs to Smart Blue Roofs

Blue roofs are increasingly being investigated as a potentially viable rooftop stormwater control method in dense urban areas. Conventional blue roofs temporarily store runoff before releasing it at a regulated pace via passive flow-control outlets. This can reduce and delay the peak discharge, alleviating pressure on urban drainage networks. The Ontario building code permits up to 150 mm of water storage for controlled roof ponding, provided that the roof structure and emergency overflow system are adequate. Smart Blue Roofs (SBRs) extend conventional blue roof systems by incorporating sensor networks, weather data, and active flow-control mechanisms.

SBRs enable dynamic control of rooftop storage and discharge. They provide detention through controlled storage and release, while retention occurs when stored water is evaporated or reused. The shift from passive detention to an actively controlled system reflects the growing use of sensor-based and adaptive approaches in urban water management. My research is developed around the Mitacs-supported Smart Blue Roof pilot constructed by Credit Valley Conservation (CVC) at its headquarters in Mississauga. The research is being conducted at Toronto Metropolitan University in collaboration with CVC. The goal of the research is to understand and evaluate the performance of SBR across multiple scales, from neighbourhood- and street-scale implementation to individual properties.

Image: Smart Blue Roof at Credit Valley Conservation Authority, Mississauga, ON

CVC Smart Blue Roof: System Configuration and Monitoring

CVC hosts Canada’s first CSA-compliant SBR, which can store up to 67 m³ of rainwater at its capacity. The roof drains are connected to a 5 m³ rainwater-harvesting cistern, providing additional storage that supports water reuse that would otherwise be discharged to the downstream drainage system. The cistern accommodates both active roof transfers and roof overflow and supplies it for toilet flushing. The cistern also has a municipal water-supply connection to support toilet flushing when the roof water is insufficient. This approach can offset a fraction of municipal water usage and support more sustainable water-use practices. The roof ponding also provides evaporative cooling benefits, which can lower roof-surface temperature and potentially influence building energy requirements during hot summer days. Together, these functions highlight the potential of SBRs to offer multiple benefits beyond conventional stormwater control.

The CVC SBR is currently monitored using IoT-enabled LoRaWAN sensors. The LoRaWAN sensors enable low-power, long-range wireless transmission and provide frequent observations in near real time. The study includes high-resolution monitoring of rooftop water level, water temperature, solar radiation, and weather parameters, including air temperature, humidity, rainfall, atmospheric pressure, and wind speed. These measurements are used to understand the SBR’s storage dynamics, develop a roof water balance, and evaluate the system performance.

Image: Rainwater Harvesting Cistern at Credit Valley Conservation Authority, Mississauga, ON

Lead Editor: Sukleshwari S