Green plot ratio: an ecological measure for architecture and urban planning

Current research on sustainability of cities has favoured the implementation and conservation of greenery in the urban context. The benefits of plants are not just environmental but recreational, aesthetic and emotional. The full benefits of plants and the role they play in the ecology of cities remain to be mapped out but the general significance of plants appears to be uncontested. This paper proposes a new architectural and planning metric for greenery in cities and buildings. This new metric, the green plot ratio (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 ground area. The green plot ratio is simply the average LAI of the greenery on site and is presented as a ratio that is similar to the building plot ratio (BPR) currently in use in many cities to control maximum allowable built-up floor area in a building development. GPR allows more precise regulation of greenery on site without excluding a corresponding portion of the site from building development. It provides flexibility to the designer while simultaneously protecting the green quota in the design. This concept has been applied in a number of design competitions in which the author has collaborated with colleagues and various architectural practices. It has also been adopted as a planning requirement by the client authority for one of the competitions for which the author has entered. While seen as a fundamental and important metric, GPR is not in itself an indicator for all the ecological relationships between plants and cities. A larger set of related metrics need to be developed.