Greenroofs: A Solution to the Ailments of the Urban Heat Island Effect

Original Paper; Produced for Virginia Commonwealth University, Master of Urban and Regional Planning; Fall 2013 URSP 650: Environmental Planning; Instructed by Dr. Avrum J. Shriar

November 2013

GREEN ROOFS: A SOLUTION TO THE AILMENTS CAUSED BY THE URBAN HEAT ISLAND EFFECT Carson Charles Lucarelli, Graduate Student of Urban & Regional Planning L. Douglas Wilder School of Government & Public Affairs, Virginia Commonwealth University Richmond, Virginia, USA

Key Words Anthropogenic  Built environment  Evapotranspiration  Green roof  Greenhouse gases (GHG)  Impervious surface  Urban agriculture  Urban environment  Urban heat island effect (UHIE)

Greening rooftops is one way to combat the litany of ailments caused by the effects of the sun on man-made surfaces. This phenomenon, more commonly referred to as the urban heat island effect (UHIE), plagues cities around the globe with higher core temperatures, greater energy consumption, and poorer air quality. This paper attempts to synthesize existing information available on how green roofs mitigate these problems as well as explore the benefits of such roofs through case studies from across the globe. Research will conclude with policy recommendations.

Introduction One facet that nearly all urban environments share is their propensity to attract heat due to the high prevalence of man-made materials and impervious surfaces (Rosenzweig, et al.). This urban heat island effect (UHIE) causes the surrounding microclimate to become hotter. The research aims to purport that in the midst of growing concerns over climate change (Gore) and environmental degradation, cities [today] have an ethical responsibility to reduce their energy demands and resort to more sustainable practices to preserve the environment.

Chiefly, this document purports that the greening of rooftops is a smart, sustainable, and ethical tactic in improving our cities and mitigating the urban heat island effect.

Studies from Texas to Estonia have shown that cities with greater concentrations of urban vegetation have improved urban air quality, lesser storm

water issues, and even use less energy when the vegetation acts as a shading for buildings (Berndtsson et al.). These studies provide substantial backing for planners and scientists who understand the benefits of these roofs, and continue to push for policy reform.

URBAN HEAT ISLAND EFFECT (UHIE) The urban heat island effect (UHIE) is a change in the microclimate that results from the heating of man made surfaces by the sun (Rosenzweig et al.). In addition to heating the surrounding climate, the UHIE has a myriad of [negative] effects including (a.) lessening urban air quality [by decreasing evapotranspiration] (b.) increasing energy demand and; (c.) decreasing quality of life (Santamoris et al.). This negative interaction is typically highest on calm summer/fall days when sunlight exposure is the longest. The UHIE is also exacerbated by other factors like automobile emissions and urban industry (Rosenzweig et al). The UHIE possess a risk globally because the effects are accelerated by highly reflective surfaces like metal, glass aluminum; which are common building materials (Rosenzweig et al). Dark materials that absorb heat such as asphalt, concrete, and darker roofing material (EPA) also intensify the effect. In cities with older building stock, such as Richmond, the problem can be further compounded as a result of an inefficient insulation system (Pitt). As buildings heat up due to agining insulation, cracks and gaps, and dark colored roofs, energy demands rise. Building energy accounts for nearly ½ of all energy use in the United States, and 40% of the GHG emissions (Pitt); therefore it is

chiefly important to recognize strategies the strategies that countries have taken to lessen their impact on the environment and mitigate the UHIE. The UHIE is of great concern to many cities across North America due to the fact that as much as 30% of the urban footprint can be attributed to building rooftops (Dvorak et al.). It is because of this a solution must be found. Many would argue that green to calm the effects of the UHIE significantly. Furthermore, rooftop greening does not require developing virgin land, but rather makes use of available, underutilized space.

Green Roofs Urban environments that lack a solid green infrastructure network suffer from a wide range of issues; and as studies have shown, green roofs, are one of the solutions (Berndtsson et al.). A green roof is a layer of native vegetation that is sandwiched between multiple permeable and semi-impermeable layers that facilitate drainage and provide a suitable environment for “agriculture� (www.greenroofs.org). This system allows such vegetation to reside primarily on top of a roof; either pitched or flat. These roofs are not only psychologically and aesthetically pleasing (Teemusk, et al.), but also provide an array of benefits for the environment.

Green roofs can be costly up front, ($10-$25 per Sq. Ft) (Environmental Protection Agency) but typically are self sustaining, require little maintenance ($0.75 per square foot / year), and benefits are actualized very quickly. These roofs will typically outlast the life a conventional roof, too; 25 years v. 50 years

(Yale). Biologist recommend using native varieties of plants and have even found that small, broad leaf succulents are ideal for water retention, and higher rates of evapotranspiration (Berndtsson, et al).

The water retention properties of these roofs are the primary catalyst behind their ability to clean up the atmosphere. When plants absorb moisture, they release the oxygen and water vapor into the atmosphere. When this is done on a large scale, i.e. a green roof top, the resulting microclimate cools and air quality is improved. The thermal insulation properties of the impervious layer also provide substantial insulation to the rooftop, where heat is often absorbed (EPA).

Green roofs also play a substantial role in mitigating storm water run off, which is a major non-point source polluter that threatens drinking water and the quality of our watersheds, bays, and tributaries (Marsh) .Storm water runoff is a problem for urban environments due to the prevalence of impervious surfaces with do not permit ground water recharge at the site; as a result, water is channeled using man-made pipes and often mixes with local water systems.

(Marsh).

Berndtsson et al. investigated the role of rooftop vegetation in mitigating storm water runoff. While their study did not conclude definitively that such roofs play a substantial role in improving run off water quality, green roofs were noted for their ability to improve air quality, and lessen the over-all contribution to run off; as these roofs can retain up to 75% of the annual load dumped on them. This is turn reduces demand on aging sewage infrastructure and increases evapotranspiration (as discussed above). Baskaran et al. also found that in cities

with older, combined sewage overflow (CSO) systems, that green roofs can play a crucial role in lessening CSO overflow episodes; which result when antediluvian systems become inundated with exorbitant run off and as a result, dump excess loads containing contaminants into nearby bodies of water as a mitigation tactic (Source). Mentens et al. reached similar conclusions with their study in Augustenborg, Sweden, but added that if CSO’s overflow episodes are to avoided more frequently, then green roofs alone are not the solution. Their study recommended coupling green roofs with storage reservoirs/cisterns than can handle CSO overflow loads. This, in union with green roofs, significantly reduced overflow episodes and did not require the development of virgin land (Mentens et al). As noted, the ability of a green roof to mitigate storm water run off also enables them to “clean” the micro-climate through evapotranspiration and thus mitigate the effects of the UHIE. This topic will be explored further.

The remaining categories will analyze how green roofs can remedy a variety of environmental issues caused by the UHIE.

THE ROLE OF GREEN ROOFS IN COMBATING URBAN AILMENTS CAUSED

BY THE UHIE (a.) Urban Air Quality / Temperature Roof top vegetation in urban environments mitigates the UHIE in a number of ways, primarily by increasing evapotranspiration. Evapotranspiration, which is earth’s natural cooling process, is described by the USGS as the “sum of all evaporation and transpiration”. This process releases residual water vapor

[absorbed by plants] back into the atmosphere and, like human perspiration, cools the environment, improves air quality, and provides natural humidity (USGS). Recalling that rooftops comprise nearly 30% of a cities building footprint, one can begin to see how wide scale green roofing could substantially impact the UHIE and reduce urban temperatures while at the same time, improving urban air quality. In an era predominated by automobile use, the UHIE is also noted for increasing smog due higher temperatures in the surroiudning environment; this can be explained by a lesser rate of evapotranspiration. As mentioned above, green roofs improve evapotranspiration, thus making the microclimate less conducive for low-lying particulate; aka smog. (Santamouris et al.) Teemusk et al. also reached similar conclusions in their study in Estonia, which concluded that evapotranspiration from vegetated roofs improves microclimate conditions. Their study also acknowledged that green roofs are a sustainable alternative to increase green infrastructure, as it is an infill tactic utilizing existing space; vice virgin land.

(b.) Building Energy Demand The United States, which leads in global solar energy production, is still a country that is heavily dependent on fossil fuels for energy (EIA). Planners and scientist in recent years have begun to understand that one way to mitigate building energy demands and reduce GHG’s is through greening rooftops (EIA).

In Greece, Santamouris, et al. conducted an extensive investigation on how a green roof installed at a childcare nursery impacted the building’s energy

demands. Their study showed that demand for cooling energy decrease by roughly 12-24% during hot summer months. This can be explained by the nature of the roof as a layer of insulation; studies have shown that the thermal properties of impervious roof surfaces improves energy demand, particularly during cooling months. (Dvorak et al.). The prevalence of vegitation also cools the atmosphere through evapotranspiration; which as noted above, cools the surrounding climate, thus lessening cooling energy demand. While their [Santamouris et al.] study did not show a direct correlation to lesser demand in heating energy during winter months, it does demonstrate that green roofs can substantially narrow building energy demands during the summer months, even in a Mediterranean climate. It is important to note that Teemusk et al. conducted a similar study in Estonia and reached the conclusion that extensive rooftop cover of at least 80% is needed for efficacy.

A recent article published by Yale however, contradicts the claim that green roofs do not mitigate heating costs; The Morgan Process and Distribution U.S Post Office facility in New York City expects over $30,000 in savings on energy bills following their green roof installation; 75% savings in the summer and 40% in the winter respectively. This installation is over 2.5 acres and is New York’s largest green roof.

Policy Related to Green Roofs Green roofs are the solution to a litany of the problems that the UHIE inflicts on cities. Barriers to success, however, can be blamed on existing policies

that lack stronger incentives and create exorbitant red tape for applicants.

Examples from here and abroad were examined and found that a wide range of innovative ideas is necessary in order to foster a successful “environment” for rooftop greening.

(a.) Copenhagen Denmark has long been recognized in the planning realm as a leader in sustainable practices for their investment in multimodal infrastructure and high quality of life (APA). To take things one step further, the city has passed legislation that requires green roofs for all new buildings with roofs pitched at 30degrees or lower. Copenhagen understands the impact that humans have on the environment, and this policy is reflective of that ideal. This progressive tactic would have wide scale positive impacts if passed here in the United States; especially in cities like our nation’s capital; where building energy accounts for 75% of all energy used! (EPA).

(b.) Holland Amsterdam, Holland is another northern European city that has been recognized for progressive planning and environmentally sound policies (APA).

Amsterdam, which plans to be “carbon-neutral” by 2025, has extensive green roof coverage and policies in place that favor them (PRI).

Despite being rather low maintenance, green roofs do require periodic up keep; typically fertilization and general preservation. It is important to note that

fertilizers can pose a risk to urban runoff quality if time-released variants are not used; roofs fertilized with conventional measures that become supersaturated can leachate those [fertilizers] into the storm water (Berndtsson et al.) and add to the pollution levels.

Amsterdam has recently taken steps towards procuring such fertilizers in a more sustainable route; by recycling human urine from public urinals to extract natural phosphates; a fertilizer for vegetation (Heap). This practice is not only sustainable, but also lessens demand on city finances for foreign fertilizers which typically are manufactured under unethical labor conditions in countries like China, Tunisia and Egypt (Heap). Amsterdam has estimated that urine from 1,000,000,000 individuals (per annum) could yield 1,000 tonnes of green roof fertilizer (Heap)!

(c.) United States The United States has experienced a steady increase in green roof coverage over the last decade and interest in the subject has grown extensively (Bates). The total coverage in the United States increased by 24% between 2011 and 2012; 5,588,098 additional Sq. Ft. added through over 900 certified projects (www.greenroofs.org). These increases can be partially attributed to recent tax incentives passed in 2005 that have attempted to streamline the process, create incentives/rebates ($1.80 per Sq. Ft tax credit) and allow for further expansion of the green roof network. Although these figures are encouraging, much of the growth has been concentrated in major cities such as Washington D.C., Chicago,

New York, and Philadelphia (www.greenroofs.org), leaving much room for infill.

Green Roofs for Healthy Cities does however anticipate additional growth in the coming years to places like Hampton Roads, Cincinnati, and Nashville, indicating that the trend may be expanding. In the midst of this shift in thinking, planners, politicians, regions and lawmakers should work together to craft greater incentives that compliment the growth of green roofs in these regions.

Policy Recommendations Policy reform plays a pivotal role in creating an atmosphere for change. As seen above in case studies, there are many innovative measures being undertaken to streamline rooftop greening, but more is needed.

A recommendation for localities here in the United States would be to look at progressive countries like Denmark and Holland and understand how these places were able to garner support for their initiatives. While the political climate in both places is different, there is much that can be learned from the Scandinavian model.

Another measure that could be used to raise capital for incentive packages would be to propose an increase tax on carbon and fossil fuels; which are known to be high GHG contributors. Ideally, the tax increase should be managed as a TIF (tax increment financing) program and the additional revenue should be channeled into separate accounts to be used for statewide incentive programs.

The US can also learn from some policies that are close to home, that could be implemented across the board. Portland, Oregon has a unique incentive program that is worth noting; a $5 grant per Sq. Ft. for “eco-roofs” (Stutz).

Chicago was recently offering up to $100,000 in grant money for green roof start ups; however they are inundated with requests and are no longer accepting applications. Out west in San Francisco, their local government has begun expediting applications through a streamlined process. And our neighbors to the north in Vancouver, Canada have enacted legislation that requires green roofs for all commercial and residential buildings greater than 5,000 square meters (http://myplantconnection.com).

As evident, there are numerous policy incentives and measures in place that create the legal “environment” necessary to foster green roof growth.

Virginia, and other states not yet on board should strongly review existing policies from here and abroad.

Conclusion This exploration has shown green rooftops have the capability to curb the urban heat island effect, and its aftermath effects. At the end of this discussion, it is now clear that green roofs around the globe are (a.) improving urban air quality (b.) lessening temperature in the surrounding microclimate and; (c.) reducing building energy demand. When applied on a large scale, green roofs have shown to combat the UHIE significantly, and improve air quality and building comfort. All this leads to fewer GHG emissions. Further policy revision is needed in order to

continue the upward trend in green roofing The United States has taken initials steps towards streamlining the process, however many localities have been left in the dark, without knowledge or financial incentive. The Federal government, therefore, should work with law makers and planners to development a policy revision that would include compulsory green roofing in all new buildings; government / commercial / residential; as seen in Amsterdam. This measure will place pressure on builders and citizens towards thinking more sustainably. As seen in Amsterdam, one green roof policy has now lead to a highly profitable urine harvesting program.

This multiplier effect could also have economic benefits for the community as well; as it would open a new market for innovative ideas. Rooftop green is smart, ethical, and for the most part sustainable practice, as long as innovation exists.

The UHIE affects nearly every American City. And with plenty of available roof top space, the country stands poised to benefit from cooler cities, cleaner air, and lesser building energy demand. In order to foster this type of change, progressive policies, like the ones discussed, must be in place.

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