Vegetated Roofing Systems – wind of change
#ecoinnovation #sustainability #greenroofing #vegetatedroof
ENVIRONMENT
Green roofs reduce urban heat island effect (UHI), stormwater runoff, purify rainwater and capture airborne particles [smog, heavy metals and volatile organic compounds] which has a positive effect on air quality.
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ECONOMIC BENEFITS
Extended roof life, reduce consumption of energy and they are good noise insulators.
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SOCIAL BENEFITS
Natural looks amongst concrete constructions
“Leave the roads, take the trails”.
– Pythagoras
Vegetated or green roofs offer multiple benefits to urban areas. They help manage stormwater, reduce energy demand, mitigate urban heat island, improve air quality, and enhance biodiversity. As a result, many municipalities are offering various forms of incentive programs to encourage green roof adoption. From a global perspective, Green Roof policies are mainly concentrated in Europe and North America, where more progressive policies encourage their implementation.
Many green roofs are located on high-rise buildings and lakefront properties that experience high wind. They must be secured against wind forces to meet performance requirements and ensure public safety. The Green Roof Construction Standard governs the design and construction of green roofs and sets out the minimum requirements to meet the city’s objectives. On the issue of wind, the standard requires an engineer-stamped report providing design wind pressures for green roofs and outlining how they are addressed. However, technical information on wind resistance of green roof was lacking.
Wind effects on modular vegetated systems
Vegetated modules contain mature vegetation that are pre-grown on mats or in trays and delivered at near complete vegetation coverage. Compared to traditional built-in-place systems, modular systems have the advantages of significantly shorter establishment time and lower maintenance needs. The mature roots bind the growing medium together, and the high vegetation coverage protects the medium from scouring. Research has also shown high vegetation density increases surface roughness and reduces wind forces experienced by the green roof. As a result, the German FLL Green Roof Guidelines recommend using a pre-vegetated systems on high wind areas. Wind tunnel studies showed the weight and design of the vegetated modules, such as trays and mats, govern their wind uplift behaviour.
Exceptions
Wind suction creates uplift force on the vegetated modules. When the uplift force exceeds the module weight, it can become airborne and overturned. Vegetated mats also reduce the net wind uplift forces through pressure equalization. Their large size (1 x 2 m [39 x 78 ft] typical) allows the uplift force to be shared over a larger area, making them more difficult to lift. However, mat uplift can still occur if the wind is high enough (e.g., at the corner region of the roof) when the net uplift force is greater than the mat weight.
Design and Rules for "Vegetated Roofing Systems"
Vegetated modules come in a wide range of weight. They also vary in material and design, so the degree of pressure equalization differs considerably from one assembly to another. Therefore, it is necessary to test and determine the wind resistance. This can be done using the CSA A123.24 standard test method. The standard determines the wind resistance of modular vegetated roof assembly (MVRA), consisting of a roofing system (RF) and a vegetated system (VS), when subjected to dynamic wind flow and loading cycles. It is applicable to modular vegetated systems that are pre-grown off-site with a minimum of 80 per cent vegetation coverage.
Like any building envelope, vegetated roof assemblies must be designed properly to resist wind forces to ensure durability and public safety. Designers should follow best practices from existing guidelines. Engineers should ask green roof suppliers for the wind resistance of their system and follow the wind design process to select the appropriate assembly for their projects. Alternatively, some green roof suppliers retain professional engineers to perform the wind design process on behalf of their clients.
Vegetated Roofing Systems - Forecast
Technicalities aside, the EFB [European Federation Green Roofs and Walls] considers that lack of urban green space in our cities can be addressed by our industry. If all urban citizens by 2030 were to have at least 5 m2 of green roofs or walls each, the current population would lead to an additional 1,82 billion m2 of green roofs and walls in Europe. Using current prices the green roof and wall market would be worth in the region of over € 62 billion market. Of course, this figure is likely to be much higher as by 2030 the urban population will have grown further.
Green systems have gone through the roof? No way!
In a world revolving around environmental sustainability, Condor could only bring additional expertise and ideal solutions to the table. The most suitable slab formwork system, in fact, may be the ticket to a faultless green roof. With a team of engineers working on custom projects, everyone is on a safe side when it comes to cutting-edge but cost-effective plans, always ahead of the pack. Going the extra mile is worth when the quality of the environment we live in is the ‘roof of the matter’.
NOTES:
- Claus, K. Rousseau, S. Urban Forestry & Urban Greening, Volume 11, issue 4 https://doi.org/10.1016/j.ufug.2012.07.003
- A review of green roof incentives as motivators for the expansion of green infrastructure in European cities 22630/PNIKS.2019.28.4.58
- Article “The Green Revolution Spreading Across Our Rooftops” https://www.nytimes.com/2019/10/09/realestate/the-green-roof-revolution.html
