Building a Smart Blue Roof

We’ve built a smart blue roof system and upgraded the rainwater harvesting system at our head office building. During operation, we’ll be able to assess the real-world performance of the system and understand how to scale this technology in the local industrial, commercial and institutional sector and in communities across Canada.

Benefits of Smart Blue Roofs

Smart blue roofs can be built on top of flat-roofed buildings common in the commercial, industrial and institutional sector which make up approximately 20 – 30 per cent of total urban areas. Smart blue roofs control the release of rainwater in three ways:

  • Hold rainwater until it evaporates from the rooftop, also providing evaporative cooling benefits
  • Send rainwater to a harvesting tank where the water can be reused
  • Slowly release rainwater into the municipal stormwater system

The use of modulating control valves within the roof leaders of CVC’s head office allow water to be captured on the roof surface, which can prevent flooding and attenuate peak stormwater runoff volumes. Smart blue roofs are a form of green infrastructure (GI). GI features are sustainable technologies and practices that manage rain to reduce the risks of flooding, protect water quality in streams and build resilience in a changing climate.

With increased risk of flooding due to more extreme and unpredictable rainfall patterns across Canada, there is a greater need now for innovative approaches to stormwater management, particularly in highly urbanized areas. The concept of smart blue roofs has emerged for greater stormwater management potential and benefits compared to vegetated green roof systems. Piloting and implementing a smart blue roof at CVC’s office will allow us to determine and report on the actual costs and benefits of such an innovative system.

Project Phases

In 2017, CVC received $175,000 in federal funding from the Federation of Canadian Municipalities to assess the technical and financial feasibility of implementing a smart blue roof on our administrative office as well as its scalability in the broader industrial, commercial and institutional sector where large, flat-roof buildings are common.

Key findings include the following:

  • The building has a parapet height of 400 mm. Structurally, the rooftop can hold up to an average of 130 mm of precipitation (equivalent to 40m3 across the roof area) thus capturing the 100-year storm.
  • The smart blue roof system can meet non-potable water demands of 8.84 m3/day, exceeding our building’s current non-potable water demand of 5.68 m3/day.
  • By storing water on the roof, a typical air conditioning unit will see a reduction of 11.6 GJ/year translating into an annual electricity savings of 3,210 kWh, or about $302 and a GHG reduction of about 0.2 tonnes CO2e annually.
  • The estimated cost to implement a smart blue roof on CVC’s Building A roof is $365/m2.

In July 2020, CVC received over $280,000 in funding through an Intact Adaptation Action Grant from Intact Financial Corporation to build and evaluate the performance of a smart blue roof system at CVC’s head office.

Between August 2020 and December 2021, together with Enviro-Stewards Inc., Interpump Ltd. and WSP Inc. consultants, we finalized a smart blue roof design and upgrade to the rainwater harvesting system. In January 2022, the City of Mississauga approved CVC’s building permit application.

The smart blue roof will be equipped with the following main components:

  • A water-proof segregation barrier segregating the smart blue roof area from the remaining roof section
  • A set of new emergency overflows complementing the existing four roof drains
  • A set of flow control modulating automatic valves responsible for facilitating rooftop storage and delivering rainwater to the basement cistern
  • A new set of secondary emergency overflow scuppers
  • Monitoring and control equipment, including level sensors, temperature sensors and flow meters
  • Bird-repellent tape
  • A complete rainwater recirculation and treatment system to be located in the existing third floor mechanical room.

Project construction began in the Summer of 2022. The construction project team consisted of CVC, Enviro-Stewards Inc., Interpump Ltd., Firenza Plumbing and Heating Ltd., WSP Canada, PAC Building Group, and TRIO Roofing Systems Inc. 

Construction occurred in four (4) stages: 

  1.  Rooftop Construction 
  1.  Modulating Control Valve Installation 
  1.  Third Floor Water Recirculation and Treatment System 
  1.   Basement Rainwater Harvesting Upgrades 

The construction of the smart blue roof surface coincided with the replacement of CVC’s roof assembly. Since the rooftop was expected to hold a maximum of approximately 40,000 L of rainwater, a seamless, liquid-applied polymethyl methacrylate (PMMA) roof membrane and electric field vector mapping (EFVM) leak detection system (provided by International Leak Detection) were included as part of the new roof assembly. A seamless membrane would help protect the underlying materials from water penetration, and the EFVM system allows CVC to identify leaks, if they occur. TRIO Roofing Systems Inc. is certified in the application of PMMA. 

The use of modulating control valves is a key mechanism for harvesting rainwater. The roof leaders of CVC’s main office were retrofitted with two (2) modulating control valves that can open to allow roof drainage or close to pond water on the roof surface. These leaders were each retrofitted with a valve and overflow pipe to ensure that water can be captured on the roof, while also ensuring that water bypasses the valve and drains from the roof if a safe maximum water level is reached. This safe maximum was determined with a structural load assessment, which was completed by WSP Canada. 

The third floor of CVC’s main office was equipped with treatment units that would allow the water that is captured on the roof surface to be actively treated appropriately under the CSA Standard for Rainwater Harvesting Systems (CSA B805-18). Micron filters (to remove debris), an ultraviolet disinfection lamp (to kill bacteria and viruses), and a chlorination unit (to avoid recontamination) were all installed to provide this treatment. The Ontario Building Code states that water cannot be ponded on the roof of a building for more than one (1) day at a time, due to public health concerns. However, the City of Mississauga permitted CVC to keep water on the roof for up to six (6) days, provided that sufficient treatment is provided. 

Before the smart blue roof project was commenced, drainage from the roof surface was directed to CVC’s rainwater harvesting cistern, which is located in the basement. This is still the case, but the water drained from the roof is now treated to the same standard that is provided on the third floor. This includes filtration, ultraviolet disinfection, and chlorination. The basement treatment system differs in that it includes settling tanks. The internal plumbing of the smart blue roof system was completed by Firenza Plumbing Heating Ltd. 

Some key performance indicators that will be monitored over the next two years are:

  • Total volume (m3) of stormwater removed from the storm sewer system
  • Total peak flow reduction (m3/s) to storm sewer system
  • Estimate savings on the annual stormwater charge
  • Estimate annual water savings from rainwater reuse
  • Estimate annual energy savings from rooftop evaporative cooling

Other questions of interest that will be explored are:

  • How does building scale stormwater management benefit both the landowners and the municipality?
  • What is the cost to operate a network of blue roof systems that provide the equivalent stormwater control as a stormwater pond retrofit?

We look forward to sharing results and lessons learned with our project partners and the broader community once the system is operating.

Project Partners

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