Blue roofs , unlike green roofs which uses plant and soil, blue roofs are designed to temporarily hold rainwater on flat rooftops. They delay in releasing then in drainage system. This is simple and effective planning specially in dense cities across US, UK or canada.
As urban populations grow and climate changes become more frequent, cities around the world are now focusing to manage excess rainwater more effectively becouse traditional stormwater systems are overwhelmed which leads to flash floods. In this article we will see key blue roof benefits and about blue roof stormwater management.
Top 10 Blue roof benefits
Blue roofs are not just flood preventing tool they offer a lot of benefits for cities dealing with rapid urbanization, outdated infrastructure and climate problems. Below I have mentioned 10 major blue roof benefits representing it a valuable part of sustainability.
1. Delay in stormwater runoff
This is the primary benefit, Blue roof temporarily stores rainwater and then release it slowly overtime. This delays peak discharge into storm drains which reduces the risk of street-level flooding, sewer backups and waterlogging during heavy rainfall events.
2. Reduces pressure on urban drainage system
Blue roof lighten the immediate burden on aging sewer system and treatment plants via staggering the release of rainwater directly into the drain. It is helpful in tier 1 old cities (london newyork) which have combined sewer system. According to NYC Department of Environmental Protection, blue roof can reduce peak stormwater flow by upto 80% during heavy rainfall.
3. Helps control combined sewer overflows
Nowadays many cities used combined sewer systems where stormwater and wastewater share the same pipe. These storm water can be treated but when they are mixed they cannot be treated. During storms this untreated sewage overflow into rivers. Blue roof can delay and reduce inflow.
4. Lowers risk of basement flooding
Those buildings which are made with Blue roofs experience less runoff spilling into surrounding areas. It create Lo chance for water entering basements parking garages and street level properties. New York City Blue Roof Pilot monitoring found that it can reduce peak stormwater flow by 30-85%.
5. Improves water quality
By slowing down runoff, sediments debris and pollutants can be easily trap before they enter into the natural water bodies. Some newly made systems can be combined with filters to clean stormwater before discharging it.
6. Support climate resilience
Nowadays more intense rainfall events are being predicted hence urban blue roof act as adaptive infrastructure. It will be scalable and effective in protecting dense cities from climate driven water challenges.
7. Enhancing performance of other infrastructures
When urban blue roofs are used with bioswales, rain garden or green roofs they perform better. Blue roof deliver water at controlled rate which prevents overload.
8. Provide temporarily cooling effect
Detained rainwater can provide a mild cooling effect by evaporation. Water absorb heat from surrounding and evaporates and cool down it’s surroundings. It is called latent heat of evaporation. it is beneficial during summer storms in heat prone cities.
9. Allow for smart monitoring
Modern urban blue roof can be equipped with sensors, valves and weather based automation which makes them a part of city’s smart water management network. Data from these system can optimise performance during extreme weather.
10. Easy to Retrofit on flat
Unlike green roofs, urban blue roofs requires less structural reinforcement and it can often installed in existing rooftops with minimal modification. This makes them cost effective for retrofits on office buildings, schools and apartments.
Blue roof stormwater management
Speed and amount of rainwater hiting the storm drains is one of the biggest problems in modern cities. Conventional flat roofs typically channels the rainwater into gutters and sewers, which creates a surge of runoff that can lead flood or sewer overflow.
According to U.S. EPA – Stormwater to Street Trees Guide, urban areas with traditional roof and Pavements generate around 5 times more runoff than natural landscape.
Blue roof system explained:
Blue roof store rainwater temporarily on the rooftop surfaces by using specialized trays or controlled flow drains. Instead of rushing into stormwater system at once, rainwater in blue roof stormwater management are held back and released slowly over time. This process is also known as detention or flow moderation. This is done by using :
- Shallow detention trays or reducing that sit beneath or on the roof surface
- Controlled floor drains that release water slowly over time.
Depending on the design Blue roof may include :
- Modular trays or tanks for holding water
- Adjustable roof drains or orifices to control outflow rate.
- Advance blue roof stormwater management may also include Sensors or smart valves.
And through this blue roof can :-
- Reduce peak runoff volumes
- Delay the timing of runoff which prevents system overload
- Lower the risk of localised flooding
- Improve the performance of green infrastructure like bioswales and rain gardens.
This capabilities make blue roof valuable in dense cities where space is limited and even small reduction in stormwater runoff can protect streets, basements and publics infrastructure.
Why blue roof are important for urban areas
- A single Blue roof can delay run of by hours giving City storm water systems more time to process water.
- In a localised storm, multiple Blue roof can reduce peak runoff volume across building which helps to protect infrastructure downstream.
- It minimizes combined sewer overflows, especially in older cities like New York, London and chicago.
- It also pairs well with other green infrastructure like bioswales, green streets and rain gardens.
Limitations of urban blue roofs
Blue roofs required rooftop to store water which add extra weights on the building and not all existing buildings are capable to hold extra load hence it create a sense of collapse. Sometimes Blue roof are not properly installed which cause leakage issues and especially if drainage are blocked. In some cases ponding water can remain too long.
In colder regions like Canada or UK standing water can freeze which creates ice loads and drainage blocking. To counter this issue you can make sure for proper insulation, drainage design and freeze thaw resistant materials are essential. Blue roof needs regular inspection and debris clearing. Hence neglecting maintenance can reduce performance.
According to U.S. General Services Administration (GSA) – Roof Asset Management Guidelines, structural retrofitting costs for blue roofs can range from $5 to $20 per square foot depending on the complexity.
FAQ
What is difference between blue roof and green roof ?
Urban Blue roofs are designed to temporarily stores rainwater and then it slowly release them into drainage system. It helps to prevent overflooding and drainage system failure. On the other hand green roof support whole biodiversity, it involves vegetation that absorbs rainwater and provide insulation. Blue roof stormwater management is different from green roof but both have their own benefits.
Are blue roofs sustainable for all buildings ?
Clearly No. Blue roof are installed during construction of the buildings or they are retrofitted, but under some conditions. The rooftop shoul be able to hold extra weights of rainwater and hence they are best for commercial industrial or multi-family buildings.
How much water can a blue roof manage ?
A well designed blue roof can 1 to 4 inches of water per rain event. The exact amount also depends on the system type and roof area. On an average it’s 25 – 100 mm of water.
Dp blue roofs required special permit ?
In many cities like New york or Chicago blue roofs should be in favour with buildings and local stormwater designs. So you should always consult with your municipality before installing it.
Conclusion
We know that cities are facing challenges due to rising rainfall intensity and urban flooding hence blue roof stormwater management becomes a practical scalable and cost effective way to overcome this situation. We came across many blue roof benefits, wether it is installed or retrofitted it will be always beneficial for tier 1 cities. As awareness among us grows the possibility of blue roof stormwater management to become a usefull infrastructure also increases. Stay tuned with ventrofy.
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