About Kevin Songer - The Author
Kevin Songer is a green roof botanist and environmental lawyer, who helps architects, landscapers and engineers design and install both nature irrigated, native plant green roof systems and food/permaculture vegetated roof creations.
Prior to establishing an urban core volumetric green consultancy Kevin and his wife, Judy operated a Florida native plant and organic herb/permaculture nursery for many years. In 2009 Kevin was awarded the USGBC, North Florida Chapter’s Award for Water Conservation and Landscape Design for his work on the LEED Platinum Villa Paraiso project. His work in green roofs includes design, construction and subsequent successful hurricane simulation testing on a sloped, extensive mat-based nature irrigated green roof with the University of Florida and he is presently overseeing installation of a nature irrigated green roof for the first LEED Platinum commercial building project in Jacksonville while involved in design of plant based water purification systems for a large sustainable Saudi project that also includes vertical green.
Kevin’s passion is found in helping his clients understand existing project site conditions and work to develop cost-effective green roof design options. Though he finds value in all volumetric green projects, Kevin’s passion lies in partnering with clients to create two important yet distinct and different types of green roofs. Kevin’s work with water conservation has led to involvement with design of green roofs irrigated by rain, dew and fog, roofs he refers to as ‘nature irrigated’ and primarily populated with endemic native plants. Additionally, Kevin works with design and installations of food and ethnobotanical green roofs, believing urban rooftop permaculture holds the key to solving hunger issues.
The content is of these articles is the solely the opinon of the author and not that of livingroofs.org
This four part series will discuss in detail green roof elements required for successful nature irrigated and native plant green roof design in Dry and Arid Climates. Though some background data references the U.S. the approach is valid worldwide.
Part One - Introduction - Why a Nature Irrigated Green Roof?
The purpose of the series is to afford the green roof designer an opportunity to consider the green roof they are designing as “a web, community or network of individuals arranged into a self-sustaining and complex hierarchy of a pattern and process.” Importantly, the material presented in the series considers successful design of nature irrigated green roofs a result of biophysical feedback between both living and non-living components “sustaining bio-diversity” and integrated with “complex and regenerative spatial arrangement of types, forms and interactions".
In simple terms, a nature irrigated, native plant green roof should be thought of as a complex ecosystem similar to the native ecosystems found on and adjacent to the site before construction, with similar vegetation and irrigated with rainfall. When a green roof is designed to utilize rainfall as principal irrigation, it can be referred to as ‘nature irrigated’. However, one important component missing from a nature irrigated green roof is the site native groundwater hydrology. Lacking groundwater, the nature irrigated green roof ecosystem will rely on rainfall, dew, fog, frost or other condensed atmospheric water vapor for survival.
We will come to see a successful nature irrigated green roof with native plant species as a synthesis of project site botany, weather, climate and ecology. However, designing a nature irrigated green roof with endemic native plant species or area friendly permaculture species can become complicated and frustrating to project designers, who are used to using stock nursery plants and irrigation with their landscapes.
Why then go to the trouble of designing a nature irrigated green roof? Why not just design a green roof with stock landscape plants or green roof plants already widely used, such as succulents, using fertilization and recycled water irrigation, such as stored rainwater with potable water for backup? Specifying proven plants is one way to ensure probable green roof success, and capturing, storing and recycling water is important and should always be always be a part of all green roof projects to the extent practical.
However, if green roofs are to be truly sustainable then their design and construction should be based upon sustainable principles. As an alternative to proven landscape type green roof plants, native species can be chosen based upon their close biophysical relationship to the area and ability to survive with native rainfall patterns and other local climatic conditions, provide endemic wildlife with appropriate habitat, clean stormwater, sequester carbon, produce oxygen and create a ‘sense of place’ for the community.
Interestingly, according to the USEPA, Americans use approximately 1.5 billion gallons of water every day on landscaping. Contrast this over-looked wealth and waste to the realization that two hundred million hours each day are spent by families across less developed nations without adequate water infrastructure in securing daily domestic water supplies, some carrying heavy jugs of muddy water on their backs great distances.
In the U.S. we use twice as much water for landscaping than the number of gallons of gasoline we burn in our automobiles daily. With the present U.S. population estimated to be about 311,000,000 persons, landscape water use is on the average about 5 gallons per person per day, or about 19 liters per person per day. Yet fortunately many governmental agencies are presently encouraging use of native species and wildflowers acclimated to reduced watering or nature based irrigation.
So, if sustainable development practices call for conservation of water in the landscape then irrigation in green roofs should be no hidden exception.
Because roof ecosystems are subject to significantly harsher biophysical conditions than most ground level landscapes, industry response sometimes has typically been one of adding irrigation and fertilizers to hopefully mitigate additional heat, dryness and desiccating wind stressors that typically have an impact on green roof plants. Moreover, because the green roof industry here in the US is still relatively young there is a lack of detailed design data to assist in planning and installing nature irrigated green roofs.
Fortunately water conservation practices in green roof design can be simple and cost-effective. Though we will delve deeply into design theory in this paper, effective nature irrigated green roof design theory can truly be best understood by spending time outdoors in and around the project site, looking up and paying attention to what is already there. We shall see that though we can model design variables in an attempt to analytically predict ‘what works best on a green roof’ sometimes a walk through the town, looking up to see what plants grow naturally in gutters, in the cracks of mortar and across roofs, provides the most useful design information.
Ultimately however, green roofs should be examples of how Green and Sustainable Designs can be achieved. A successful nature irrigated green roof will afford great understanding and education of true area ecology, provide wildlife corridors and habitat, clean pollutants from stormwater, sequester carbon and provide oxygen. A nature irrigated vegetated roofing ecosystem will serve to inspire others to consider creating further urban core volumetric green.
Understanding Rooftop Ecosystems
Wikipedia offers an enlightening definition of the term ‘ecosystem’ with the phrase “a web, community or network of individuals that arrange into a self-sustaining and complex hierarchy of a pattern and process.” Moreover, Wikipedia further describes ecosystems as capable of creating biophysical feedback between both living and non-living components “sustaining bio-diversity” and integrating into “complex and regenerative spatial arrangement of types, forms and interactions”.
Considering a nature irrigated roof in terms of a self-sustaining ecosystem is appropriate and scientifically accurate, especially with respect to the phrase “complex and regenerative spatial arrangement of types, forms and interactions". These ‘types, forms and interactions’ comprise the design variables we will examine and try to better understand as we develop the components of a nature irrigated green roof.
Once we think in terms of a potential roof as an ecosystem we make the first step towards understanding the basics of green roof design. However, we must consider the roof to be a community of many different and varying ecosystems. Most roofs will possess distinct areas with different biophysical characteristics. We will call each of these individual roof area ‘individual roof ecosystems’ or ‘roof polygons’. Each polygon will represent the boundaries of a roof section within which the section has similar types, forms and interactions.
Furthermore we can identify these types, forms and interactions in geophysical terms such as; sun exposure, wind exposure, temperature ranges, rainfall accumulation, etc.
A basis of design for the nature irrigated green roof will be developed by considering and analyzing the types, forms and interactions of the roof’s geophysical characteristics.
Finally, the process of designing a nature irrigated green roof begins with development of a project site pre-condition model, followed by the defining of roof polygon dimensions (either existing or proposed), development of a post construction model specifying recommended plant selection and placement and final design.
Pre-Condition Ecosystem Types, Forms and Interactions
The green roof designer must intimately know the project site’s ecosystem characteristics before being able to create a nature irrigated green roof design. The modeling of before and after comparison is referred to as ‘pre versus post modeling’ and summarizes the site ecosystem’s biophysical types, forms and interactions.
The development of a site pre-condition site model and subsequent modeling pre versus post requires collection of empirical data such as;
• Monthly wind speed and direction
• Daily temperature graphs - low, high and mean
• Seasonal air water vapor & humidity characteristics
• Monthly rainfall amounts, daily trends
• Sun exposure, shade amounts
• Adjacent and indirect impact factors
• Existing plant types
• and much more as we shall discuss.
The biophysical data collected from the project site forms the basis of the design model’s ‘pre’ component. Data is collected from the roof or where the roof will be built (field) or from local records and assembled to define the project site’s existing ecosystem characteristics. The ‘pre’ model defines background conditions.
Assembling the background data can be time consuming.
Importantly, much biophysical data is usually available for most metropolitan areas from local universities and governmental agencies. Yet because each project site is uniquely an ecosystem in and of itself and each roof may contain multiple potential ecosystems, we strongly recommend the collection of on-site data over a period of at least twelve months.
Again, field collected data provides the most useful analytics, yet may not always be available. In the absence of field collected data or to verify field collected data, climate data can be referenced from certain organizations. Internet and online climate resources include;
• http://www.worldclimate.com - a useful portal for climate resources
• http://www.ncdc.noaa.gov/oa/ncdc.html - the National Climatic Data Center (primarily data for the United States)
• http://www.climatedata.eu - Climate data for Europe
• http://www.almanac.com/weather/history/NH/Dublin/2009-12-28 - daily rainfall data since the early 1990’s for many US cities
• http://www.drought.unl.edu/dm/archive.html - US Drought maps and data - useful validation resource
• http://www.climate-charts.com / a great world climate website with a collection of in-depth climate maps and data, including the informative index map available from http://www.climate-charts.com/World-Climate-Index-Map.html
• http://bonnet19.cs.qc.edu:7778/pls/rschdata/rd_prcp.prcp_data_access Informative world precipitation Oracle-based data collection, excellent for general validation purposes
• and other sites available on the internet. Google searches will provide numerous additional resources.
For field data to be representative of what the nature irrigated green roof will experience in the field, several years of analytical input is needed to accurately predict optimum design criteria. However in the absence of available long-term data collection opportunity, a twelve month window may be used to verify local adjacent or regional long term weather data.
For field measurements a standard weather station with data gathering capabilities is recommended. Depending upon the size and layout of the roof more than one weather station may be required. Refer to the Roof Polygon Section for information on defining the boundaries of a roof polygon and subsequent placement recommendations of weather collection and biophysical data development.
There are many data sensors, data loggers and data interpretation software available on the market.
In addition to collecting analytical biophysical data, be sure to visit your project site regularly at various times of the day, morning, mid-day and during the evening to obtain an understanding of how your green roof will ‘fit’ with the site. Sometimes you will find the missing piece to the pre-post model puzzle has always been right there, yet previously unseen on the site.
To be continued...
In Part Two, we will review the fundamentals of the rooftop ecosystem. Part Two will contain four sections, including;
• Understanding rooftop ecosystems
• A Definition of the Project’s Existing Ecosystems, Biophysical Traits and Rooftop Polygons
• Pre-Condition Ecosystem Types, Forms and Interactions, and
• Data Collection