Smart Blue Roofs: A Sustainable Solution for Urban Cities

Flooding is the most expensive natural disaster affecting Canadians, with insured losses averaging $1.8 billion annually. When we take away natural surfaces and pave them over, water moves faster through our watersheds and does not get stored onsite. Climate change has intensified rainfall patterns, leading to shorter, more intense rain events, while urbanization has increased impervious surfaces, exacerbating the risk of flooding. Cities have multiple approaches to slow and store water so it does not cause flooding, including green spaces, permeable surfaces, and stormwater ponds- and innovative new technologies- such as blue roofs. 

At Credit Valley Conservation (CVC) in Mississauga, Ontario, the first Canadian Standards Association (CSA)-compliant Smart Blue Roof demonstrates how innovative green infrastructure can revolutionize urban water management. This system not only mitigates risks of flooding but also serves as a rainwater harvesting tool, supporting non-potable water use such as on-site toilet flushing.

What Is a Blue Roof?

A Blue Roof is a novel type of green infrastructure, designed to temporarily store rainwater on rooftops by using advanced logic-based softwares. By capturing and controlling runoff, it reduces peak stormwater discharge in the sewer systems and provides evaporative cooling, which can lower energy costs.

Key Features of the CVC Smart Blue Roof System

The Smart Blue Roof at CVC is a versatile system designed to address urban water management challenges. As a proof of concept, it has a surface area of 344 m² and can store up to 40,000 litres of rainwater for non-potable uses such as toilet flushing and landscape irrigation. Its seamless PMMA (polymethyl methacrylate) membrane provides insulation and ensures efficient water retention. Advanced treatment systems, including filters, Ultra Violet lamps, and chlorine, maintain water quality for safe reuse and meeting thresholds. Additionally, smart valves and a recirculation system dynamically regulate water flow based on weather conditions and building requirements. Together, these features enable the system to mitigate risks of flooding, conserve water, and enhance energy efficiency.

Scaling Smart Blue Roofs for Urban Resilience

The potential of Smart Blue Roofs extends beyond individual buildings such as the CVC headquarters. When implemented at street or neighborhood scales, these systems can:

1. Reduce run-off volume and slow urban water down.
2. Provide water reuse like onsite toilet flushing, irrigation, industrial applications, and vehicle washing.
3. Lower urban temperatures, as the evaporation of water cools the surrounding environment.

By integrating Smart Blue Roofs into urban planning, municipalities can improve their resilience to extreme weather events while promoting sustainable water management practices.

Policy Challenges and Opportunities

In Ontario, the Ontario Building Code (OBC) regulates blue roof installations, requiring water to be removed within 24 hours and having a maximum water depth of 15 cm. These standards were developed with the intention of protecting public health by preventing water fouling. However, they may limit the full potential of blue roofs in providing energy savings and cooling benefits. Further, many of these standards were developed without an assessment of whether the blue roofs pose a public health risk.

My PhD research aims to challenge these constraints by exploring the public health implications of blue roofs and their performance while maintaining safety standards.

As a public health PhD student, I collaborate with CVC and the Urban Water research team at Toronto Metropolitan University (TMU), which includes experts in civil engineering (Darko Joksimovic & Afsana Akhie), architecture (Hitesh Doshi & Dorothy Johns), and public health (Kimberley Gilbride, Ian Young, Fatih Sekercioglu, and myself) supervised by Angela Murphy. Together, we aim to advance the scalability of Smart Blue Roofs while ensuring water quality meets safety standards. 

2024 Sampling Season Highlights:

The 2024 sampling period spanned from May to October, with daily water sample collections when water was on the roof. Samples were collected from the blue roof, recirculation system, and the pre- and post-treatment units in the basement. Once collected, samples were transported to Kerr Hall at TMU, where in-lab testing at Dr. Gilbride’s lab assessed both microbial and physicochemical parameters. Microbial parameters included total bacteria, total coliforms, fecal coliforms, Salmonella, and Legionella, while physicochemical parameters encompassed temperature, pH, conductivity, total dissolved solids, Ultra Violet transmittance, chemical oxygen demand, and total organic carbon.

Water quality was monitored in relation to external factors such as ambient temperature, precipitation, wind direction, evaporation, and chlorine residual. Results showed that water quality was generally below the safety thresholds set by the Canadian Standards Association and the Canadian Guidelines for Domestic Reclaimed Water for Use in Toilet Flushing and for Irrigation when sufficient chlorine residual was present. Observations suggested that the water could potentially be held on the roof for a longer period of time (more than 24 hours). The upcoming 2025 sampling season aims to refine methodologies and conduct a comprehensive case study to strengthen the evidence supporting an extended timeframe to keep the water on the roof. This work highlights the potential of blue roofs to optimize urban water management while adhering to public health standards.

Advancing the Future of Urban Water Management & a Call for Action

The CVC Smart Blue Roof exemplifies how technology can address critical urban challenges by integrating rainwater harvesting, cooling cities, and reducing the risks of floods.

Extreme weather events are becoming more frequent. With ongoing research, policy innovation, and community engagement. Smart Blue Roofs could become another method to reduce the volume and speed of urban runoff, ensuring cities are better prepared for future climates.