Monday, December 15, 2008

Green Plot Ratio

A recent link from World Landscape Architect uncovered a short but interesting post from The Daily Star by Faysal Kabir Shuvo on a concept called the Green Plot Ratio (GPR). It is interesting in reinforcing the idea of vegetated architecture and the need for greenery in cities and buildings in combating the effects of urban heat islands. While our typical response is to mitigate this through artificial conditioning of our environment, the use of vegetation is a contributor to the benefits.

:: image via Jetson Green

Via The Daily Star: "...there are several benefits in increasing the amount of greenery in citiesenvironmentally, aesthetically, and recreationally. From supplying oxygen, food and most of the necessary commodities the extent of services rendered by the plants and trees are multifold: pollution control, heat reduction, ecological habitat restoration, increasing scenic beauty etc. Diverse researches are being carried out to integrate environmental and ecological thinking in urban architecture and design to improve local climatic situation in terms of temperature reduction and attenuating the effect of UHI as well as conserve the existing greenery or compensate the green loss by culturing green above the ground."

The article identifies four factors as play in UHI mitigation: climate, hydrology, carbon storage and sequestration, and biodiversity. "The above strategic and multi-dimensional usefulness of greenery in urban built environment called for using a common metrix that can be used as a sustainable indicator for urban design. Therefore, based on the famous planning tool namely, Building Plot Ratio (in our country which is used as Floor Area Ratio) and a biological parameter named Leaf Area Index (LAI), the tool called Green Plot Ratio(GPR), developed and successfully used in many urban designs by a famous landscape architect of Singapore, Dr. Ong Boon Lay who is also a faculty of National University of Singapore."

:: image via Jetson Green

By using a combination of FAR (allowable building area) and LAI (leaf to ground ratio), we can determine the GPR, which is "...defined as the average LAI of the greenery on the site." Why is this important? Because it offers a value-driven conceptual framework for determining the amout of site coverage that is not generic, but is based on the quality of landscape coverage. For instance, grass equals 1, shrubs equal 3, and trees equal 6-10, depending on the canopy coverage.

While the article mentions that this is valuable for determining how much to offset in terms of ecological value when natural areas are displaced with development. "These values are very much helpful in determining to compensate the amount of green loss due to new development. Suppose, a new mixed development has been proposed in an area which is naturally vegetated and a portion of that vegetation may undergo destruction during development. So we can easily estimate how much LAI we are losing and how we can compensate by planning plantation in the form of vertical gardening, roof gardening and re-plantation."

An edited example from the article: "... the proposed development on an area of 500 SqM , 30 SqM of grass land, 50 SqM of shrub land and 20 SqM of matured tree are needed to be destroyed ... we can compensate the loss by the form of allocating green provision on the building top, wall, vacant place or maintaining green patches within buildings like park connector or greenways planning... But it is true that the compensated green will not be same like the existing one in terms of its ecological values and services. Because at the roof level the maximum LAI value of 3 (shrub, bush) (Fig-1) can be achieved and cripplers that are used as the vertical gardening or roof gardening replicate grassland."

:: images via The Daily Star

What does this mean in terms of Veg.itecture? While not offered as a panacea, it's a way of beginning to try to equate the concept of greening that is not merely flat succulant roof greening or green screen panels - but is based on a scientific ratio of the plants coverage - applying the ground science to the sky: "A new term, skygarden has been introduced to refer to planted landscapes built above the ground: in intermediate floors of high-rise buildings or at the rooftop. It is true that a roof garden cannot be equivalent to a similar sized garden on the ground as well as a high-rise building wrapped with green cripplers on its roof facades may not be effective as a mature tree of similar size that is lost due to the development but in face of fast urbanization and consequent loss of natural vegetated green lands achieving high GPR in the above form undoubtedly will contribute to a large extent to reduce the effect of habitation loss, worse environmental effect etc. Therefore rather than looking for modern technologies to combat the effects of climate change or global warming significant concentration should be put on enlightening ideas and innovations regarding green revolution in the architecture and planning starting from an individual building scale to a city scale."

:: image via Jetson Green

Another related topic which I will cover is the Berlin Biotope Area Factor (BAF), which has been incorporated in North America through the new Green Area Factor (GAF). Look for a post on this soon.


  1. Interesting. Shuvo's Green Plot Ratio (GPR) is somewhat like the concepts used in surface water runoff computations and the continuum from impervious surface areas to an ideal "forested condition."

    It would be useful to be able to model the quality of landscape coverage using various assumptions and designs.

  2. Jim. There are definitely some similarities with the runoff calculations... it's interesting to see how much variables would have to be generalized, or conversely how much data would be needed for an accurate accounting of the GPR.

  3. Last building is fantastic, is it possibly.

  4. Shuvo's Green Plot Ratio is actually a concept developed by me. Shuvo happens to be a student of mine. Can this blog be revised to reflect the correct authorship? I believe Shuvo referenced me correctly in his article - Dr Ong Boon Lay, Department of Architecture, National University of Singapore.


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