Image Source: http://www.treehugger.com/files/2008/06/green-roof-vacation.php
Designing the Fifth facade
Contributing to Sustainability in the city
Shikha Keshan
Introduction: The fifth façade or the roof in a building can be used as a very important tool for sustainable planning and design in architecture. In today’s fast growing cities and rapid urbanisation, the environment is being compromised and an urgent need is felt to restore a balance and provide the concrete cities with lungs and reconnect man and nature. Not only is there a necessity to build buildings which do not negatively affect the environment, but there is an urgent need to contribute to the environment and improve the immediate surroundings and context. Green roofs or planted roofs are not only the most suitable tool for doing so they also help in bringing down the energy requirements in a building substantially. Planted roofs can be very instrumental is dealing with numerous environmental and practical problems which characterise the cities today. Not just architecturally and in terms of aesthetics can green roofs add value to a building, but when implemented in a large scale they help in tackling urban issues like Urban Heat Island Effect, storm water management, cleansing of air in polluted areas and reducing the amount of pollutions delivered to the local drainage system via surface runoff of rainwater.
Faroe Islands, Near Denmark 1
ACROS Fukuoka , Fukuoka City, Japan 2
What are greens roofs? Green roofs or living roofs are vegetated roofs which transforms urban roofs into green space and gardens that improve air and water quality and save energy. A green roof assembly includes, as a minimum, a root repellent system, a drainage system, a filtering layer, a growing medium and plants, and shall be installed on a waterproof membrane of an applicable roof.
Image showing green roof section 3
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Elements of a green roof A planted roof mainly consists of the following parts:
the overgrowth; seedlings, mosses, grasses and other plants, and depending on the thickness of the substrate layer even larger shrubs and small trees. the substrate layer; organic material, sometimes complemented with inorganic or even artificial material in which the plants grow. a water passing filter-membrane that separates the substrate layer from the underlying layers.
drainage-elements or -material
protecting layers, a root stopping layer, and a water stopping layer, either by itself or combined.
the carrying roof construction, possibly completed with an extra heat-insulating layer.
Vegetation, plants
Growing medium
Filter membrane
Drainage element
Moisture mat
Root barrier Water proof membrane Thermal insulation Vapour Control Structural roof deck
Two main classifications of green roofs- Extensive green roof - Intensive green roof
Intensive green roofs refer to rooftops that accommodate large plants including trees, full lawn, etc. This type of green roofing requires a significant depth of soil as well as lot of maintenance, similar to maintaining a park or large garden.
Image showing the various layers of green roof 4
Extensive green roof is the most convenient of all types of green roof systems and involves roof covering with a thin layer of growing medium and vegetation that requires minimal care and maintenance. Image showing extensive green roof 5
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What are the advantages of greens roofs? - Reduction in ambient air temperature, energy use, and utility costs - Help to cleanse the air and water - Utilize local and recycled materials - Extend the life of the roof - Help in storm water management - improve aesthetics - create green space for humans and wildlife while providing a psychological and physical respite from urban surroundings.
Image showing intensive green roof 6
How green roofs can help improve the urban environment and make our cities more sustainable? Storm water management, use and control along with improvement in the quality of water Green roofs act as sponges for the city and help make use of the relatively clean rainwater which we otherwise let run into the stormwater drains and mix with sewage. Rainwater can be used by the vegetated roofs and excess rainwater can be collected and used for various activities like flushing, cleaning and gardening. Most old cities have combined sewer systems where waste water from storm drains and sewage pipes is intermingled. During heavy rainfall, runoff from impervious surfaces like concrete rooftops overburden the sewer systems causing untreated sewage to overflow into the city’s waterways and also contaminate lakes, rivers and other fresh water sources. Green roofs reduce stormwater volume and slow down water flow, thus helping to alleviate the pressure on stormwater infrastructure systems. Green roofs capture and retain huge amounts of water that otherwise would go down the storm drains, absorbing anywhere between 50 to 95 percent of the rain that falls on site. The depth of the substrate and the plant mass affect the retention rate.
Graph showing the reduction in runoff volume 7
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As with natural soil/plant systems, green rooftops reduce runoff problems by a variety of means, including: The storage of water in the substrate Absorbing water in the root zone Capturing and holding precipitation in the plant foliage where it is returned to the atmosphere through transpiration and evaporation Slowing the velocity of direct runoff as it infiltrates through layers of vegetated cover Green roofs also help to reduce the eutrofication and pollution delivered to the local drainage system and ultimately to the rivers and other fresh water sources by improving the quality of storm water which flows into the water bodies.
Image showing the various layers of green roof 8
Nitrogen is one of the major pollutants leading to eutrofication of water. Airborne nitrogen compounds fall to the ground in dust, raindrops or gravity and when these compounds are carried with stormwater runoff, they contribute to eutrofication. Green roofs help in reducing the nitrogen content in the rainwater which ultimately gets discharged into the drains. Most heavy metals and nutrients present in the rainwater are retained by the soil substrate and vegetation instead of being discharged through the sewer system into rivers or streams. The harmful nitrogen present in the raindrops gets converted by the soil into a nitrate form which the plants take up as they grow.
Green roofs contribute to improved water quality not only by retaining and filtering the rainwater through the soil and root uptake zone, but also through: · The vegetation, which slows down the water through friction and root absorption. · The foliage in particular, which collects dust, transpires moisture and provides shade. · The binding of potential pollutants to clay and organic matter in the roof top soil matrix The Commission Water Management of 21st century suggests a 3-step strategy for handling water in the city Hold Store Drain off
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Models for the design of urban water plan like the Slow down model and the Infiltration model, as discussed by S. P. Tjallingii, make use of the 3-step strategy for better water management. Greens roofs also fit aptly into the 3 step strategy and the slow down model. The substrate in the planted roof holds the rainwater and slows down the process of discharge. Excess water which is not taken up by the roots of the vegetation can then be drained off.
Urban Heat Islands Urban heat island effect is a growing concern in most cities today. Hard paved concrete surfaces have replaced the greens and this in combination with pollution from cars and industries have led to a significant rise in the temperature of cities in comparison to the less urbanised suburbs and the fringes of the city. This effect of increase in temperature (from 2 to 10 degrees hotter) in urban areas is known as the Urban Heat Island effect.
Image showing the difference in temperature urban and rural areas 9
A heat island develops when buildings, roads, sidewalks, and rooftops replace natural vegetation. Unlike natural surfaces that moderate temperature through evaporation from soils, transpiration from plants, and shading, the built surfaces are made of materials like brick, asphalt, and concrete which are impervious to water. Materials like asphalt and concrete soak up heat during the day and then reradiate it back into the Earth’s atmosphere after sunset as thermal infrared radiation. This contributes to global warming. Used on a large scale, green roof infrastructure could help reduce the urban heat island effect by lowering ambient air temperatures. A 2002 study in Toronto by Environment Canada estimated that urban temperatures could dip by 1 to 2°C if just six percent of the city’s roof tops were green.
Image showing the urban heat island effect 10
Reduction in Energy Consumption The variation in the internal temperature in a building with a green roof is comparatively much lower than a building with a flat concrete roof. The mass of the green roof especially with the soil substrate acts as a thermal barrier and prevents major swings in temperature. The multi-layered roofing systems insulate the building against heat and reduce costs of cooling
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the building. The evaporative process on a planted roof acts like a natural air conditioner – heat is “pulled” off the surface of the roof as moisture is wicked away. Green roofs can also be combined with solar power projects so that that roof not only helps in reducing energy consumption but also helps in creating renewable source of energy.
Implementation of Green roof in architecture and design Designing with green roofs or planted roofs is not a modern concept. Green roofs or sod roofs have been used in Scandinavian countries for centuries. The modern way of constructing greens roofs with manufactured layers of mediums to support vegetation and growth is a relatively new concept developed in Germany in the 1960s.
The Vilhelmsro school, Denmark, BIG architects 12
Green roofs continue to change architecture, as architects blend buildings into the landscape and use the roofs as architectural elements, often to hide the building from view. The Vilhelmsro school in Denmark "focuses on nature and sustainability" so Bjarke Ingels of BIG designed it out of sloping landscaped bands that are integrated into the hillside. The green roofs add value to the architectural language of the school and make it more pleasing and experiential as a building. The sloping landscape and the building's sloping roofs merge into one continuous experience no matter if one is inside, outside, on the ground floor or walking across its green roofs.
The Vilhelmsro school, Denmark, BIG architects 12
The green roof facilitates passive energy measures such as mitigating heat island effect, acting as thermal mass and evaporative cooling qualities, rain water runoff is reduced, collected and stored for nonpotable usage, cross-ventilation is also encouraged through operable windows and overlapping openings. This project by BIG architects is a good example of how implementing green roofs not only has energy and environmental benefits but also leads to innovative and creative designs and provides a stimulating spatial quality and flexible use.
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Companies today provide all the various layers and technology required for installation of green roof with sophisticated systems to suit multiple building types and forms. The installation of green roof has high initial costs but installation process and maintenance has become easy.
Conclusion Green roofs, which have been referred to as the fifth faรงade in this article, can help us to mitigate the rising urban pressures and issues of global warming and degrading city environment, while at the same time contributing to an architecturally varied and pleasing cityscape which connects back to the green. It helps us bring back the green to the horizontal while at the same time providing economic and energy benefits. Initiatives and subsidies are being provided by government authorities to encourage the practise of using green roofs. As architects and designers we can contribute to the growing popularity of green roofs by integrating it with our design process and thinking about it as an important energy saving and ecologically contributing tool from the concept level.
Diagrams showing the effects of installing a green roof in the Vilhemsro school 12
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Bibliography: S.P. Tjallingii ; Hydrological Processes and Water Management in Urban Areas (Proceedings of the Duisberg Symposium, April 1988). IAHS Publ. no. 198, 1990, http://iahs.info/redbooks/a198/iahs_198_0323.pdf, , accessed 2011 Linda S. Velazquez ; Organic Greenroof Architecture: Sustainable Design for the New Millennium Making the most of your building's "fifth façade" © Wiley Periodicals, Inc. Environmental Quality Management/Summer 2005 , http://www.greenroofs.com/pdfs/newsEQM_VelazquezPart1.pdf , accessed 2011 Landphair, H.C. ; Landscape architecture construction, Elsevier, 1979 http://www.lid-stormwater.net/greenroofs_benefits.htm http://www.earthpledge.org/gr/combined-sewage-overflow http://www.greenroofs.com/ http://www.greenroofs.org/ http://www.big.dk/projects/vil/
Sources for images (all images accessed on 07.04.2011) 1. http://www.treehugger.com/galleries/2009/06/green-roofs-arechanging-architecture.php 2. http://www.scholtensroofing.com/RooftypesVancouver/Green-Roofing-Vancouver.html 3. (Source:http://progressivetimes.wordpress.com/2010/10/04/on e-roof-two-roofs-green-roofs-blue-roofs/) 4. http://www.move.com/trends/green-roofs-for-greener-cities/ 5. http://www.citywindsor.ca/002746.asp 6. http://www.iees.ch/cms/index.php?option=com_content&task= view&id=26&Itemid=47 7. http://www.greenroofs.org/index.php/about-green-roofs/greenroof-benefits 8. http://www.lid-stormwater.net/greenroofs_benefits.htm 9. http://www.greenyour.com/home/homeimprovement/roof/tips/plant-a-green-roof 10. http://www.ruf.rice.edu/~sass/UHI.html 11. http://insitearch.com/blog/category/architecture_matters_colu mn_hauser/page/2/ 12. http://www.big.dk/projects/vil/
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