Blue roofs

Blue roofs can be a very economical and low maintenance way to manage undesirable rainwater on a flat roof. For rooftop retention on moderately sloped roofs, a green roof is going to be a better choice. On steeply sloped roofs, rainwater harvesting, or diverting roof leaders to a landscape integrated LID is a more appropriate alternative. 
==Overview==
Preceded by green roof and flow control roof drain systems, blue roof systems are an innovative green technology for flood and drought resilience and adaptation. Blue roof systems temporarily capture rainwater using the roof as storage and allow it to evaporate and/or to be used for non-potable requirements (i.e. irrigation, toilet flushing, truck washing) and ultimately offset potable water demands. Any remaining water can be gradually released into the municipal stormwater system reducing peak flow rates. Additionally, during the summer season, rainwater ponded on a flat roof can cool the interior of a building and reduce air conditioning pressures through evaporative cooling. As such, smart blue roof systems are advantageous to both the private and public sector.
Blue roof systems regulate rooftop runoff by storing and controlling the release of rainwater, thereby reducing the potential of overflow in the municipal sewer system and thus, the potential for localized flooding. Combining a blue roof system with rainwater harvesting (RWH) allows for rainwater reuse and provides additional benefits. Blue roof systems are a popular stormwater management option for flat roof buildings, particularly within the industrial, commercial and institutional (ICI) sector (which make up 23 - 30% of most urbanized areas) Credit Valley Conservation. 2020. Automated Real-time IoT Smart Blue Roof Systems for the IC&I Sector for Flood and Drought Resilience and Adaptation Technical and Financial Feasibility Study. Credit Valley Conservation, Mississauga, Ontario. https://sustainabletechnologies.ca/app/uploads/2019/02/Smart-Blue-Roof-Lit-Review-Feb-2019.pdf. The appeal is the relatively low cost and simplicity of modelling and forecasting performance,. 
The fundamental components of a blue roof are:
*A flat roof
*Flow control device(s)
==Planning==
 Things to consider when planning a rooftop detention systemhttps://www.pwdplanreview.org/manual/chapter-4/4.6-blue-roofs
Advantages	Limitations
*Do not require ground level space, so particularly well suited where ground space is limited or sites with large flat roofs
*May not require additional sewer connections 
*Easy to retrofit if structural support and waterproofing are adequate
*Relatively low cost compared to green roofs (no vegetation requirements)
*Potential for evaporative cooling and reduction of urban heat island effect	
*Must be regularly inspected and maintained 
*Limited application on sloped roofs or sites with small building footprints
*Do not provide any co-benefits such as habitat creation or air quality improvements associated with vegetated practices
*Mechanical systems and other rooftop architectural features must not be adversely impacted by ponded water
==Design==
Water can be slowed in running from a flat roof (up to 2%) through the use of: 
*drain covers (most common), 
*small check dams or weirs across the roof deck, or
*modular tray systems.Massachusetts Clean Water Toolkit, Rooftop Detention (Blue Roofs), Retrieved 9 October 2018 from http://prj.geosyntec.com/npsmanual/rooftopdetentionblueroofs.aspx
All roofs in Canada must be designed to support peak snow loads, providing capacity for supporting an equivalent weight of ponded water. The Ontario building code permits designers to assume that snow and water loads are not cumulative, up to a maximum depth of 150 mm (water equivalent), if precautions are taken to prevent flooding by providing a sufficient number of roof drains with overflows. It is therefore uncommon for roof water detention systems to be designed to permit more than 150 mm of water to accumulate. This also means that these systems can be retrofitted onto existing roof structures that have been designed to support conventional snow loads.Richard Hammond (2017). Evaluating Green and Blue Roof Opportunities in Canadian Cities. UWSpace. http://hdl.handle.net/10012/11463
The Ministry of Transportation does not currently permit blue roofs to form part of a SWM plan owing to concerns over long-term maintenance; this affects relatively few projectsOntario Ministry of Transportation. (2016). Stormwater Management Requirements for Land Development Proposals. Retrieved March 7, 2018, from http://www.mto.gov.on.ca/english/publications/drainage/stormwater/section8.shtml#controls. The concerns arise from instances where building operators have found outlet control structures blocked with leaves or other debris. Without understanding the purpose of blue roof systems and flow control drains, these devices have been removed to prevent recurrence of the blockage. A study in New York City found that a modular system of trays outperformed an outlet flow control device in stormwater managementBloomberg, M., & Strickland, C. H. (2012). NYC Green Infrastructure Plan: 2012 Green Infrastructure Pilot Monitoring Report. New York. Retrieved from http://www.nyc.gov/html/dep/pdf/green_infrastructure/2012_green_infrastructure_pilot_monitoring_report.pdf. It might reasonably be expected that a modular system would present fewer opportunities for complete failure from a single action, either through clogging or breakage of a storage element.
==Smart Design==
Blue roofs can also be fitted with smart controls and electrically operated valves to regulate water discharging from the roof. The electrically operated valves can be tied to predictive weather algorithms to forecast incoming rain or snow events as well as extreme heat days. Based on the weather forecast, valves may be opened and closed to accommodate additional rain or snow loads. When coupled with a rainwater harvesting system, blue roofs increase rainwater storage capacity to meet non-potable water demand (i.e. toilet flushing or irrigation) without the need to oversize tanks. Rainwater harvesting tanks with smart controls are able to coordinate with blue roofs to draw water from the roof when the tank water level is low to meet demand and offset municipal potable water use. Credit Valley Conservation. 2018. Smart Blue Roof Project Literature Review Report. Credit Valley Conservation, Mississauga, Ontario.
==Inspection and Maintenance==
An inspection and maintenance plan is crucial to the success of a blue roof system and should be updated based on the results of the first-year post-construction monitoring. The plan should include a maintenance schedule developed for the entire life of the rooftop system. Aspects that need to be included:
#Maintenance activities required to be completed per week/month/season/year; 
#Frequency or maintenance and inspection activities; 
#Timing of said activities; and, 
#Assigning the appropriate person/consultant (entity) responsible for completing the activity should be included (Credit Valley Conservation, 2018)Credit Valley Conservation. 2018. Smart Blue Roof Project Literature Review Report. Credit Valley Conservation, Mississauga, Ontario. Retrieved from: https://cvc.ca/wp-content/uploads/2022/03/STEP-CVC-Smart-Blue-Roof-Project-Literature-Review-Final.pdf
Inspections will need to occur within 24 hours of significant rain events (>25 mm) to ensure the specified ponding depths and drain times are being achieved as per design specifications, standing water does not persist for more than 24 hours, and there are no leaks occurring due to damage to the roof membrane or as a result of other underlying roof conditions (NYCDEP, 2012a). New York City Department of Environmental Protection (NYCDEP). 2012. NYC Green Infrastructure Plan: 2012 Green Infrastructure Pilot Monitoring Report. Retrieved from: https://www1.nyc.gov/assets/dep/downloads/pdf/water/stormwater/green-infrastructure/2012-green-infrastructure-pilot-monitoring-report.pdf. 
 Recommended Inspection Activities for Blue Roofs (NYCDEP, 2012b) New York City Department of Environmental Protection (NYCDEP). 2012. Guidelines for the Design and Construction of storm water Management Systems. Retrieved from:
https://www1.nyc.gov/assets/dep/downloads/pdf/water/stormwater/stormwater-design-construction-guidelines-2012-final.pdf.
Schedule	Activity
Semi-annually under dry conditions	
*Inspect roof drain inlets to ensure in good condition.
*Inspect drain inlet screens/covers and scuppers to ensure in good condition.
*Inspect roof membrane to check for signs of deterioration.
Quarterly and after rain events	
*Inspect roof to verify achievement of water depth and drain time requirements.
*Inspect secondary drainage inlets for blockage or debris.
After snow/icing events	
*Check roof drain inlets for blockage caused by buildup of snow or ice.
Maintenance activities for blue roofs should focus on preventing clogging of drainage inlets and deterioration of the roof membrane (NYCDEP, 2012b) New York City Department of Environmental Protection (NYCDEP). 2012. Guidelines for the Design and Construction of storm water Management Systems. Retrieved from:
https://www1.nyc.gov/assets/dep/downloads/pdf/water/stormwater/stormwater-design-construction-guidelines-2012-final.pdf.. In addition, adequate maintenance of the secondary drainage system is essential to ensure its performance in the event of a failure of the roofing system. The rooftop system and membrane should be evaluated every 20 years to assess the need for replacement. Maintenance access points should be clearly identified in the plan for the system. Special training required to perform specific tasks is required for the appropriate person/consultant (entity) responsible for completing the specific maintenance activity.
 Recommended Maintenance Activities for Blue Roofs (NYCDEP, 2012b) New York City Department of Environmental Protection (NYCDEP). 2012. Guidelines for the Design and Construction of storm water Management Systems. Retrieved from:
https://www1.nyc.gov/assets/dep/downloads/pdf/water/stormwater/stormwater-design-construction-guidelines-2012-final.pdf.
Schedule	Activity	Equipment Needed
During inspections or as needed to ensure performance	
*Remove debris from drainage inlets and inlet screens to prevent clogging.
*Remove debris from secondary drainage inlets/scuppers.	
*Shovel
Winter considerations	
*Break up ice formations around inlets	
*Ice pick, small pick-axe, or other equivalent/relevant tool
Take a look at the Inspection and Maintenance: Green Roofs page by clicking below for further details about proper inspection and maintenance practices:
==Blue roofs in the treatment train==
Blue roofs can be used in combination with green roofs by employing a scaffold system to keep the vegetation rooting layer out of the ponded water. Blue roofs could also be employed in combination with a rainwater harvesting system which has daily usage demands. Coupling blue roofs with rainwater harvesting systems could offset cistern capacity requirements and supplement tank capacity deficiencies. 
==For Review==
https://www.state.nj.us/dep/stormwater/bmp_manual/NJ_SWBMP_9.8.pdf
==Providers==
===Flow control devices===
*Wade Canada
*Watts Canada
*Zurn
===Other===
These products are designed to suspend green roof (or other) systems above a layer of free water for the detention period. 
*Hydrotech
*Livegreen
==References==