Last edited 04 Jan 2021

Green plot ratio

Devised and used successfully by Singapore-based landscape architect Dr Ong Boon Lay, the green plot ratio (GPR) is a relatively recently-developed architectural and planning metric for assessing and facilitating greenery in cities and buildings. Based on a scientific ratio of plant coverage, it can be seen as an indicator of sustainability in urban design.

The GPR recognises that in urban areas, the benefits of plants are not just environmental but can also be recreational, aesthetic and emotional. Their full benefits and their crucial role in the ecology of cities are becoming more valued with the passage of time but the general significance of plants appears to be indubitable. Benefits of photosynthesis, water retention and purification, shade, sound insulation and atmospheric remediation are now seen as critical in the urban environment, in particular given the increase in pollution from vehicle exhausts.

Inspired by the building plot ratio, the GPR is based on a common biological parameter called the ‘leaf area index’ (LAI), which is defined as the single-side leaf area per unit of ground area. According to Dr Lay, the GPR is the average LAI of the greenery on a site and is presented as a ratio that is similar to the building plot ratio (BPR) currently used in urban areas to control maximum allowable developments of built-up floor areas.

The GPR is claimed to allow more precisely regulated site greenery “...without excluding a corresponding portion of the site from building development”. Designers are said to have greater flexibility when it comes to landscape design while simultaneously protecting the green quota in the landscape.

Dr Lay has applied the GPR concept in several design competitions in which he has collaborated with colleagues and architects. In one of these competitions, the GPR was adopted as a planning requirement by the client authority.

The author has stressed that while it is a fundamental metric, GPR is by itself not an indicator for all ecological relationships between plants and cities. A larger set of related metrics need to be developed.

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