Elsevier

Environmental Pollution

Volume 159, Issues 8–9, August–September 2011, Pages 2100-2110
Environmental Pollution

Green roofs as a means of pollution abatement

https://doi.org/10.1016/j.envpol.2010.10.029Get rights and content

Abstract

Green roofs involve growing vegetation on rooftops and are one tool that can help mitigate the negative effects of pollution. This review encompasses published research to date on how green roofs can help mitigate pollution, how green roof materials influence the magnitude of these benefits, and suggests future research directions. The discussion concentrates on how green roofs influence air pollution, carbon dioxide emissions, carbon sequestration, longevity of roofing membranes that result in fewer roofing materials in landfills, water quality of stormwater runoff, and noise pollution. Suggestions for future directions for research include plant selection, development of improved growing substrates, urban rooftop agriculture, water quality of runoff, supplemental irrigation, the use of grey water, air pollution, carbon sequestration, effects on human health, combining green roofs with complementary related technologies, and economics and policy issues.

Introduction

Green roofs entail growing plants on rooftops, which partially replaces the vegetation that was destroyed when the building was constructed. In doing so they provide numerous benefits that can help offset the negative aspects of pollution, especially in the urban environment. They can improve stormwater management by reducing runoff and improving water quality, conserve energy, mitigate the urban heat island, increase longevity of roofing membranes, reduce noise and air pollution, sequester carbon, increase urban biodiversity by providing habitat for wildlife, provide a more aesthetically pleasing environment to work and live, and improve return on investment compared to traditional roofs (Czerniel Berndtsson, 2010; Dunnett and Kingsbury, 2004, Getter and Rowe, 2006, Mentens et al., 2006, Oberndorfer et al., 2007, Rowe and Getter, 2010).

They are generally categorized as either ‘intensive’ or ‘extensive’. Intensive green roofs are frequently designed as public places and may include trees, shrubs, and hardscapes similar to landscaping found at ground level (Fig. 1). They generally require substrate depths greater than 15 cm and generally require ‘intense’ maintenance (Snodgrass and McIntyre, 2010). Intensive roofs also tend to be more expensive than extensive roofs because of the need for a more structurally sound building to support the weight. In contrast, extensive green roofs often never seen, require minimal maintenance, and are generally built with substrate depths less than 15 cm (Fig. 2). Because of the shallower depth, plant choices are limited to grasses, herbaceous perennials, annuals, and drought tolerant succulents such as Sedum. Due to building weight restrictions and costs, shallow extensive green roofs are most common. The type of roof installed can have a significant impact on the ecological, social, and economic services it provides in terms of pollution abatement.

This review will evaluate published research to date on how green roofs can help mitigate pollution, how green roof materials influence the magnitude of these benefits, and suggest future research directions.

Section snippets

Criteria for selection of articles

To be included in this review, papers had to be written in English and to maximize scientific credibility of this review they had to be published in peer-reviewed journals. The author acknowledges that much early work on green roofs was written in German, but is not readily available to most of the world and much of it was not published in peer-reviewed journals. With some exceptions, papers from proceedings of conferences were not included unless they were published within the last two years

Air pollution

Polluted air is directly attributed to declines in human health (Mayer, 1999). Nearly one-quarter of the people in the U.S. live where there are unhealthful short-term levels of particle pollution, while roughly one in ten people live where there are unhealthful levels year-round (ALA, 2010). Increased mortality rates in 95 urban areas within the US have been linked to elevated levels ozone (Bell et al., 2004). In Canada, the Ontario Medical Association attributes 9500 premature deaths per year

Carbon dioxide

There is little doubt that the earth is warming (National Research Council, 2001). Part of this may be due to natural cycles, but the increase in temperature has coincided with the industrial revolution and the burning of fossil fuels. Burning fossil fuel releases CO2 as a by-product of combustion and CO2 is often implicated as a cause because it is one of the atmospheric gases that keeps terrestrial energy from escaping into space, thus resulting in higher temperatures due to the greenhouse

Fewer roofing materials in landfills

The mechanical lifespan of a typical conventional roof is approximately 20 years. When these roofs are replaced the old roofing materials must be removed, transported, and will likely be placed in a landfill where they not only take up space, but may also leach pollutants. On the other hand, green roofs are estimated to last 45 years or longer in terms of mechanical lifespan (Kosareo and Ries, 2007). This estimate is based primarily on empirical evidence as modern green roofs are a relatively

Water quality of stormwater runoff

Much has been written regarding the ability of green roofs to retain stormwater (Czerniel Berndtsson, 2010; Carpenter and Kaluvakolanu, in press, Carter and Jackson, 2007, Carter and Rasmussen, 2006, DeNardo et al., 2005, Getter et al., 2007, Hathaway et al., 2008, Hilten et al., 2008, Mentens et al., 2006, Palla et al., 2009, Simmons et al., 2008, Spolek, 2008, Stovin, 2009, Teemusk and Mander, 2007, VanWoert et al., 2005a, U.S. EPA, 2009, Villarreal and Bengtsson, 2005). The reduction in

Noise reduction

Excess noise is not only annoying, it can lead to health problems such as hearing impairment, hypertension and ischemic heart disease, sleep disturbance, and decreased school performance (Öhrström, 1991, Passchier-Vermeer and Passchier, 2000). In urban areas, high noise levels are often a problem in enclosed spaces surrounded by tall buildings, along street canyons, and near industrial areas and airports.

Conventional roofs are generally hard surfaces so the potential to reduce sound pressure

Plants selection

All of the pollution abatement benefits of green roofs stem from the plants, because they are the components that make a green roof green. Keeping a green roof healthy and thriving will influence how well the roof performs in terms of pollution abatement. Many factors determine survival of green roof plant species including substrate depth (Dunnett et al., 2008a, Durhman et al., 2007, Getter and Rowe, 2009), solar radiation levels (Getter et al., 2009a), and climate with the limiting factor

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