Sustainable and Resilient Roofs for the Sunset and Richmond Districts in San Francisco: Greening the Bay Area Professor John Radke University of California Berkeley LD ARCH 221 White Paper 1
Problem: Sustainable and Resilient Roofs for San Francisco: Greening the Bay Area An urban forest improves the quality of life and urban environment. The presence of trees and plants brings about environmental, physical and psychological health benefits to the city by improving the desire to work and live in San Francisco. Besides increasing the ecological function of the city, urban canopy cover in the form of green roofs can also play an economic role in increasing investment opportunities and reducing building heating, cooling and infrastructure costs (SF Urban Forest Plan, 2014). Overall, the city has a very small urban vegetation canopy when compared with many other major cities within the United States. Urban vegetation canopy is defined as the percentage of the urban area that is covered by foliage when viewed from above (Watershed Forestry Resource Guide, 2015). Using aerial photos, the history of a city s urban environment can be monitored over time. In 2012, remote sensing aerial photos revealed that while cities such as Portland and New York have as much as 30% and 24% tree canopy rates respectively, San Francisco s stands only at a dismal 13.7% (SF Urban Forest Plan, 2014). SF prides itself on being one of the most greenest cities in the country based on renewable energy and zero-waste goals but it also has the lowest urban canopy cover when compared to all other major cities in the US. Despite the costly green roof installation process and potential code-policy hurdles, the known benefits of these rooftops will make San Francisco a more desirable place to live and more resilient. This study focuses specifically on the Richmond and Sunset districts located in the northwestern corner of the city. Both are home to a dense suburbia that could be potential green roof installation sites. These two districts are encapsulated by the nature that fills Golden Gate Park and the 2
Presidio and would be excellent sites for green roofs because of their proximity to the ocean, available solar potential and flat roofed buildings. Figure 1: Background image is an ArcGIS imagery layer from Google Earth images. The clipped Digital Surface Model outlines the study site (Richmond and Sunset districts) used in this paper. History/Literature Review: The trees that thrive within the vibrant city have adapted well to its Mediterranean climate since the city was first developed. Encompassed by the San Francisco Bay and the Pacific Ocean, San Francisco contains a unique landscape dominated by its weather, ecology, and geology (SF Urban Forest Plan, 2014). It is an environmentally diverse peninsula with varying degrees of livability of the vegetation. The microclimates that exist in the city can be distinguished by differences in sun, fog, and temperature, which depend on the specific region's proximity to the Bay and the Ocean (SF Urban Forest Plan, 2014). Neighborhoods 3
can house various microclimates, which inherently influences the type of tree species that is able to grow in that region. Vegetation and green roofs are important to San Francisco because of their environmental benefits. They modify the climate, reduce local and global carbon dioxide levels, reduce energy consumption, improve air quality, and mitigate storm water runoff (SF Urban Forest Plan, 2014). Currently in San Francisco, stress is placed on the sewage systems because storm water runoff floods these systems. Installing green roofs would ultimately reduce storm water runoff and delay the time at which runoff occurs, resulting in decreased stressed sewer systems. Boosting the canopy cover of the city would maximize the carbon sequestration of the urban forest in order to combat climate change (Nowak et al., 2007). Because most of greenhouse gas emissions come from vehicles, trees lining the streets could potentially reduce the carbon footprint of the city (Resource Analysis of Inventoried Public Trees, 2013). Healthier and more mature vegetation has the ability to sequester large amounts of carbon; the larger the surface area of leaves, the larger the amount of carbon can be stored in the foliage, thus providing a healthy habitat and a cleaner air quality (Resource Analysis of Inventoried Public Trees, 2013). A few public benefits of green roofs include reduction of the urban heat island effect, food production for community gardens and improved air quality (SPUR Greener and Better Roofs, 2013). A few private benefits of green roofs include noise reduction, extended life on the roof and increase in property value on aesthetics and provision of open space (SPUR Greener and Better Roofs, 2013). This study is modeled after the City of Oakland s model for installing sustainable urban rooftops on buildings. An Oakland-based nonprofit organization, Bay Localize contacted the PlaceWorks office located in Berkeley, California with the motive of 4
developing a methodology that would successfully determine locations most suitable for the installation of urban rooftops for capturing rainwater, generating clean, renewable energy and insulating building temperatures. PlaceWorks created a model that assesses urban rooftops as locations for green roofs, hydroponic gardens and photovoltaic panels. The Oakland model incorporates a second model that used the ArcGIS Spatial Analyst took to calculate the expected energy and water outputs if the urban rooftops were installed. The second step uses a specialized GIS model that correlates the solar gain characteristics against the building characteristics to determine its potential. This Oakland model was tested in the Eastlake neighborhood in Oakland and successfully identified hundreds of buildings that could host at least one type of roof (green, hydroponic, photovoltaic). This second model was not utilized in the San Francisco study due to the study s time constraints and lack of data availability. Small parts of the Oakland model will be utilized for this San Francisco study to assess the most suitable location for green roofs, in addition to a proximity-based model iteration. The methodology for this study and model requires several steps. The first step requires LiDAR data collection from the United States Geological Survey (USGS), which serves as the input for generating the Digital Surface Model (DSM) that will be used for most of the analysis carried out in the study. Step 2 requires National Agriculture Imagery Program (NAIP) data collection and further processing of this imagery in order to compute a Normalized Difference Vegetation Index (NDVI), which produces a visual image to observe live green vegetation. In addition, the NAIP imagery was further processed to carry out an Iso Cluster Unsupervised Classification to produce a 4-class image with an output that best segments the existing buildings within the study site. The third step uses the DSM to calculate the hillshade and slope of the physical features existing in the study site. Step 4 involves using 5
the Area Solar radiation Tool that considers insolation over a geographic area by calculating surface orientation and shadow effect data from the input Digital Elevation Model (DEM) that was downloaded from the USGS. The fifth step is where the model iteration iterates over the entire model to create a multi ring buffer in 50-foot increments from existing canopy cover. The sixth and final step utilizes a mathematical model to create a suitability map revealing patterns that best satisfy the study s land use strategy. Solution: This study will incorporate data from a variety of sources. This includes the USGS, the GIS Data Depot, Google Streets Map View, SF Open Data and LiDAR imagery downloaded from the USGS National Map Viewer. In addition, some data will need to be assessed in the field and included in the model manually. Data from municipal government organizations such as the Planning Department, SF Environment and the Department of Building Inspection (DBI) for San Francisco could assist the selection process of suitable buildings for green urban rooftops. 6
Figure 2: Conceptual Model for Sunset and Richmond district green roof analysis. Model Development/Timeline The model requires a series of steps in order to successfully identify buildings that would be most suitable for urban green rooftop installation. Below is a detailed conceptual model of the study. Step 1: Gather LiDAR data (.las files) of San Francisco and convert into Raster DSM tiles to then be mosaicked into DSM of study site Complete by: April 29, 2016 Image 1 7
Step 2: Gather NAIP imagery of San Francisco and perform NDVI analysis and Iso Cluster Unsupervised Classification to determine pervious and impervious surfaces Complete by: April 30, 2016 Image 2 Step 3: Use Slope tool and Hillshade tool to produce clear visuals for analysis Complete by: May 1, 2016 Image 3 Step 4: Use Solar Radiation in Spatial Analyst Tool box to assess the available solar gain and the Aspect tool to determine flat roof shape (flat, gabled, sloped). Reclassify the aspect map to only include flat facing surfaces Complete by: May 2, 2016 Image 4 8
Step 5: Perform Model Iteration that iterates over the entire model to create a multi ring buffer in 50- foot increments around the clipped SF Urban Canopy shapefile Complete by: May 2, 2016 Image 5 Step 6: Weight the SF building footprint file, the reclassified Iso Unsupervised Classification file, the reclassified Aspect file and buffered 50 foot SF Urban Canopy Cover file from the Iterative Model Complete by: May 5, 2016 Image 6 Possible Limitations There are four factors that could limit rooftop potential. These include: weight, roof type, roof access and available space. Most roofs are unable to support the loading of green roofs or to harvest any vegetation. Hydroponic gardens are a solution to this problem because they have a lower weigh coefficient. In addition, hydroponic gardens control the nutrient mixture and systematically calibrate how much feed is needed to feed the system. They require less maintenance, as they do not need to be weeded and they save water because the roots only soak the desired amount of water and the remaining water stays in the reservoir. With this type of system, 90% of rainwater can be saved instead of draining into sewer systems (SPUR Greener and Better Roofs, 2013). The type of roof is important when considering where to install a green roof as well. Pitched roofs are not conducive for gardens 9
but are optimal choices for rainwater harvesting and electric generation via photovoltaic panels. All types of roofs considered in this model need to be accessible from either an elevator or stairs. Finally, there needs to be enough space available to install some form of green roof that would produce the environmental and economical benefits discussed earlier in this paper. For example, the urban rooftop needs to be able to support the weight of a 1,000- gallon water cistern and accommodate the space required for the tank. Results: Cities around the world are currently in the process of developing green roof policy development. Europe is the farthest along in this process in that they have the most mature policies and programs (SPUR Greener and Better Roofs, 2013). In the United States Portland, Chicago and New York City are the leaders in both green roof-specific policy and in the onthe-roof implementation (SPUR Greener and Better Roofs, 2013). In studying the successes of other domestic and international cities green policies and how they have proliferated in these cities, this model will hopefully contribute to ongoing movement for building and expanding green roof policy and installation in San Francisco. Figure 3: Final Suitability Map. The darkest green color correlates to areas that are the best potential candidates for green roof installation. Figure 4: Zoomed in Suitability Map of Sunset district. The darkest green color correlates to areas that are the best potential candidates for green roof 10 installation.
The current green roof policy landscape is supportive of the development of green roofs and does exist in the city s Urban Forest Master Plan (SF Urban Forest Plan, 2014). Figure 3 illustrates that both the Richmond and Sunset districts would be suitable sites for green roof installation, however the Outer sunset would benefit more from green roof installation (Figure 4). Data geographically located in Golden Gate Park, Lincoln Park and along the beach are not incorporated in the study analysis. The results from this model are intended to provide more knowledge for SPUR s Proposed Green Roof Policy Road Map for San Francisco. The first phase in this roadmap functions to identify policy barriers to efficient roof design, clarify approval and permitting process for new and retrofit roofs and prepare the SF Green Roof Manual with design, construction and maintenance guidelines. Phase 2 hopes to then agree on official targets and goals for SF, finalize the storm water fee logistics and study temporary exemption of green roofs from property taxes. The final phase functions mostly to compile the lessons learned from policy implementation to date and to confirm the approach to mandate both public and private roofs for new buildings and those already existing. The Sunset and Richmond model addresses the already existing buildings in these districts. This study can be incorporated into the first phase of this Policy Road Map particularly in drafting effective municipal green roof policies that allow for broader installation and acceptance of green roofs. To clearly communicate the motivation for green roof installation in San Francisco, individual maps illustrating each step incorporated in this study were produced along with the final suitability analysis map displayed above (Figure 3). Embedded in SPUR s Proposed Green Roof Policy Road Map for San Francisco are steps that have successfully increased green roof development in other cities. The second step in this process is Raising Awareness 11
Through Demonstration Projects and Identifying Champions which is the primary goal of this study. Cost is cited as one of the largest barriers to date preventing green roof installation, especially on already existing buildings. A temporary incentive could be an effective way of encouraging residents living in either of these districts to invest in this opportunity. Solar incentives offered in California have been highly successful in that they encourage early adoption of solar panels, which results in a higher percentage of the installation cost covered. The Area Solar Radiation map (Figure 5) indicates that over 90% of the study site receives high solar radiation. Understanding the climate and location of the study site is imperative for the setting up and understanding the calculations performed in ArcGIS. The northwestern portion of San Francisco is bordered by to the west by the Pacific Ocean and touches the Figure 5: Area Solar Radiation Map. The orange and red colors correlate to areas that receive the most solar radiation. intersection of the Pacific Ocean with the San Francisco Bay to the north. The climatic conditions can be characterized as a Mediterranean climate, with monthly average temperatures ranging from 46-74 F. The highest precipitation occurs between December and March with an annual total precipitation of 23.64 inches. Solar and photovoltaic systems harness sunlight for productive use and can drive down insolation costs for the buildings in the northwestern part of San Francisco. Pairing both solar installations with green roofs reduces the maintenance required for the two systems individually as the plants contribute to 12
cooling the solar equipment and the green roofs are less water intensive. Because this study does not incorporate the possible limitations on rooftop potential, weight, roof type, roof access and available space, it is assumed that the houses in the Sunset and Richmond districts could host either extensive or semi-intensive green roofs. Extensive green roofs are well suited to roofs with small load bearing capacity and for sites that are not intended for a roof garden. The cost associated with this type of green roof is also lower compared to other green roof classifications. With the current high rent crisis in San Francisco, this less expensive option provides an economically feasible option for those who cannot afford more extravagant green roofs well equipped with benches, bushes, trees and water fountain structures. Semi-intensive green roofs require more maintenance, higher costs and more weight. Various grasses and perennials can be installed on these roofs but larger growing bushes and trees are still not found here. Semi-intensive green roofs are better suited for multi-story office buildings and apartment complexes that can bear the loading capacity of these heavier gardens. The maps generated from the NAIP imagery help better interpret the landscape and Figure 6: NDVI Map. The green color correlates to vegetated areas with yellow and red representing areas without vegetation. 13 Figure 7: Iso Cluster Unsupervised Classification Map. The blue color (4) correlates to building outlines with the red and purple representing impervious surfaces.
terrain that exists on the ground surface. The NDVI map (Figure 6) identifies vegetated areas and more specifically detects live green plant canopies in multispectral remote sensing data. The Iso Cluster Unsupervised Classification map (Figure 7) produced from the NAIP imagery was used to classify impervious and pervious surfaces. With the major storm water drain flooding issue in San Francisco, it would be most effective for the city to encourage green roof adoption as well as an increase of other green infrastructure if there was an economic mechanism or incentive for private property owners to treat storm water as effluent (SPUR Greener and Better Roofs, 2013). The impervious surfaces displayed in Figure 7, coupled with the already existing storm water drain issue, strengthens the argument for implementation of a storm water fee in San Francisco. Flat rooftops foster more efficient green roofs in comparison to sloped or gabled rooftops. The Aspect map (Figure 8) illustrates which areas in the study site have a flat aspect, which translates to no downslope direction on these surfaces. The flat areas displayed on the Slope map (Figure 9) calculated from the DSM are identical to the flat areas calculated using the Aspect tool. Figure 8: Aspect Map. Grey color correlates to flat surfaces.. 14 Figure 9: Slope Map. The darkest green color correlates to flat surfaces.
Conclusion: Green roofs have an amplifying effect. They positively effect the physical environment in a chain reaction form. The more that exist within the city, the more benefits that the city receives in the form of open space, storm water management, noise reduction, air quality improvement, beautification and urban cooling. With large non-profit organizations, such as SPUR, and San Francisco government sectors, such as the SF Department of Public Works, collaborating with each other, the hopes of accomplishing the near-term and longterm recommendations for what San Francisco can do to design and develop a more favorable environment for greening rooftops in the future are much higher. The results from this study prove that most building roofs within the Richmond and Sunset districts are excellent candidates for green roof installation because of their flat nature and proximity to already existing vegetation. The simulations performed for this study could be taken further by including weight, roof type, roof access and available space. With this information, detailed analysis can directly calculate gallons of water, kilowatt-hours of electricity and pounds of vegetables that could be produced on each rooftop. The information gained from this study strengthens SPUR s Proposed Green Roof Policy Road Map for San Francisco. As urban density increases, influences from the natural environment decrease and San Francisco s physical infrastructure will need to compensate for this impact. Future sustainable building designs need to be connected with the natural environment and its geographic location. The green roof installation process is moving in a positive direction day by day and will continue on this positive path over the next several years. 15
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