The Potential of Green Roof Habitats in Ireland All Ireland Architectural Research Group 2015 Conference
Noel Hughes
Report
Vancouver Conference Centre
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The aim of this report is to explore the potential for green roofs to act as habitat islands and the ability of such an approach to affect the local/regional ecology. Green roofs are a growing part of urban areas, providing numerous benefits to built-up regions. They have been proven to be capable of mitigating the urban heat island effect (Skinner, 2006; Alexandri & Jones, 2008) and reduce Image 1 - Lapwing breeding on the Green Roof rainwater runoff (Graceson, Hare, Hall, & Monaghan, 2011; Keeley, 2003). Studies have shown that green roofs can sequester carbon (Getter, Rowe, Robertson, Cregg, & Andresen, 2009) and can increase the life span of the roofs (Porsche & Köhler, 2003). However, the increasing popularity of green roofs is primarily due to the environmental benefits that they bring, particularly in urban areas (NIEA, 2005). This report will aim to establish the possibilities of green roofs to be used in a habitat creation role in Ireland. While long-term studies on small scale sites have proven that green roofs can support complex habitats in London (Gedge D. , 2002) and Basel, Switzerland (Brenneisen S. , 2005) this study aims to gauge if a similar programme of greening would be suitable for the conditions associated with Ireland’s natural habitats. 01 Ireland's Natural Habitats Ireland has a wide range of habitats and species, many of which are of special note (NIEA, 2010). Our coastal regions are of international importance for waterfowl and waders, while upland areas and bogs are renowned for their diversity in plant life and invertebrates (NIEA, 2007).
Image 2 - Ireland Grassland
Currently Ireland is experiencing significant losses to our natural habitats, commonly due to urban expansion and modern farming practices (Cooper, McCann, & Rogers, 2009). During the past decade, the UK recorded a 39% loss in area of natural environments and 27% of ‘priority species’ were found to now be in decline (Defra, May 2006), in addition to a degradation in markers that indicate an environment’s health. For example the butterfly population dropping/dropped? by 55% in the last 30 years (Defra, April 2008) and major declines in bees and amphibians (Margerison, 2008).
Ireland’s natural habitats face a number of risks. The leading cause of habitat loss was the increased demand for housing over the past decade (NIEA, 2007); especially for new housing in coastal regions where construction was commonly on virgin land (MOSS, 2009). A primary concern is the deterioration of our indigenous habitats, such as wet grasslands, bog lands and native forests. Currently the peat bogs in Ireland suffer from over grazing, excess harvesting of turf and the machining of peat in gardening products (Biodiversity NI, 2011). Additionally, the reduction of wet grassland due to farming practices has a knock on effect to migrating bird populations. The Curlew, Snipe, Redneck and Lepwing who breed on wet grassland and bogs have declined in numbers by over 50% in the Last 20 years and the common House Sparrow population has declined 19% between 1994 and 2006 (Biodiversity NI, 2011).
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02 Potential Benefits of Green Roof to Ireland’s Bird Populations Many natural habitats in Ireland are critical to a variety of avian species. Nationally supporting over 200 bird species, not including rare and migratory species (Biodiversity NI, 2011). There has been a widespread decline in the bird population of Ireland. The common House Sparrow has declined 19% during 1994-2006 and the Curlew, Snipe, Redneck and Lepwing species have declined by over 50% in the last 20 years (NIEA, 2010).
Image 3 - Wildwood Community College, Missouri, USA
Completed projects have shown the adaptability of bird species to green roof habitats. Many of Ireland’s towns, which are in the breeding and feeding range of migratory and native birds, can be retrofitted. Buildings such as the Clinic One at University Hospital of Basel, Laban Dance Centre in London and the Ducks Unlimited National Headquarters and Conservation Centre in Winnipeg, illustrate the ability of birds to dominate roof spaces which resemble their natural habitat.
Green roofs have the potential to play an important role in Ireland’s bird conservation schemes, especially in urban centres. The value of green roofs to bird populations is already recognised by the RSPB, who have issued guidelines for bird habitats on green roofs (RSPB, 2011). 04 Habitats Favoured by Rooftop Environments The environmental conditions at roof level favour the application of a number of habitat treatments (Dunnett & Kingsbury, 2008). The following habitats present qualities which are applicable to ecological specification on green roofs: Mountainous Vegetation
Image 4 - Mountain Plain grasses and shrubs on Paul Lincke Ufer, Kreuzberg, Germany
Costal Vegetation
Image 5 - Costal Meadow grasses planted on the Nassau Icehouse Brewery
These plant species that are acclimatised to the shallow soil, scree slopes or rock faces of mountainous environments possess the potential to successfully occupy a green roof (Dunnett, 2006). While rock face habitats may be slow to develop on rooftop, high altitude meadow wildflowers rapidly colonise north-facing roof sections (Grant G. , 2006). The lack of complex natural soil layer means that it is possible to construct artificial soil with mimicking properties. Maritime and coastal habitats impose a broad range of environmental stress on local vegetation. In order to survive in such ecosystems, plants must be capable of surviving in free-draining sandy soil and be tolerant to both drought and heavy wind exposure (CVNI, 2011). Additionally, the continuous exposure to salt-laden air has created plant species tolerant to airborne city pollutants (Dunnett & Kingsbury, 2008). Recent field research into how plant species spontaneously colonized urban areas and habitats (such as pavements, walls, roofs, lawns and roofs) originate disproportionately from coastal and rocky habitats (Lundholm & Marlin, 2006).
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Limestone Vegetation
Image 6 - Grass sloped roof on the Vancouver Conference Centre
Shrub & Heath Vegetation
Image 7 - Heath Planting on Sloped Roof at Schiphol Plaza, Amsterdam Airport
Arid Vegetation
Image 8 - University Hospital Basel
Reed Bed Vegetation
Image 9 - John Deere Works, Mannheim
The shallow soils that cover limestone slabs support a variety of grasses, mosses and shrubs. The limited space for root growth and grazing pressure have resulted in many plant species becoming dwarfed (Northern Ireland Habitat Action Plan, 2005). A diverse range of stress-tolerant vegetation has developed on limestone rich soils, resulting in an array of planting options for green roofs (White & Snodgrass, 2003). Habitats that exist in exposed locations have developed an array of low dense vegetation. In lowland situations these include drought-tolerant shrubs, grasses and woody plants (Gates, 1980). At higher latitudes heaths and mosses are abundant (Cooper & McCann, 2001). Because of the thin soil and exposed aspects of these habitats, their flora and fauna can rapidly adapt to conditions on most green roofs (Brenneisen S. , 2006). Vegetation that is capable of surviving the harsh temperature ranges and drought conditions of both natural and manmade arid environment are capable of existing unmodified at roof level (Larson, Matthes, Kelly, Lundholm, & Gerrath, 2004). Many of these habitats are dominated by a single flora species. Because of this, they can be easily transplanted to a green roof setting (Dunnett & Kingsbury, 2008). Flat gravel roofs are a common roof type and can be readily colonised by these plants (Grant, 2006). Given the high water retention level at roof level, it is possible to encourage the development of reeds and wetland grasses on green roofs. This habitat type has been employed on rooftops to meet a growing need to conserve and clean water discharge in many regions (Earth Pledge, 2005). The minimal soil requirements and the ability to recycle nutrients in water runoff can provide for flora and fauna, which require a permanent waterlogged environment (Coffman & Davis, 2005).
05 Impact of Green Roofs on Surrounding Environment There are many international examples of the ecological consequences of installing green roofs. The ability for a green roof to accommodate any plant species is a simple matter of careful design (Burgess, 2004; Dunnett N. , 2006). However, it is common for plants to naturally migrate to roof gardens and on occasion extremely rare plant species have unexpectedly been found happily living at roof level. In Wollishofen, Zurich; nine near extinct orchid species were found existing alongside 175 other plant species on the grass roofs of
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the local water works. This was a surprise as the green roofs were never intended to be an ecological centre when they were installed in 1914 (Landolt, 2001). Research from both America and Europe has shown that green roofs are adept at attracting and supporting colonies of insect species. Green roofs on the Ford assembly Plant in Dearborn, Michigan were shown to Image 10 - Moos Filtration Plant Wollishofen Zurich become home to 29 insect species, seven spider species, and 2 bird species within the first two years of its installation. (Coffman & Davis, 2005). Furthermore, construction laws in Basel, Switzerland were changed when a biodiversity study of seventeen green roofs were found to support 78 spider and 254 beetle species. Of which 18% of the spiders and 11% of the beetles were found to be rare and some considered endangered (Brenneisen S. , 2006). Bird species can benefit greatly from the installation of green roofs. Swifts which migrate to Ireland in late summer already inhabit many existing roofs (Biodiversity NI, 2009). Green roofs can greatly enhance the habitability of many existing structures; (Grant G. , 2006) with the sedum roof at Belfast’s Victoria Centre already becoming a home to nesting jackdaws, blackbirds and finches (Biodiversity NI, 2009). In-depth research into the occupation of green roofs by birds has been undertaken in London. A 2004 study of two roofs in East and West Sussex found that 70% of the total resources used by bird were provided by the vegetation on the roofs, i.e. feeding and nest material (Burgess, 2004). The study concludes that if careful consideration is given to green roof design, they could play an important role in securing the future of the most threatened bird species (Burgess, 2004). The most endangered species Image 11 - Laban Dance Centre, London observed on a green roof was Black Red Start (Grant G. , 2006). Between 50-100 breeding pairs of this highly endangered species was seen nesting on the green roofs of the Laban Centre and the Creekside Centre, both in the London Docklands (Frith & Gedge, 2000). 06 Benefits of Green Roof to the Urban Environments While individual green roofs will offer local environmental benefits, they are often restricted by their size (Grant, Engleback, & Nicholson, 2003). Any significant contribution to the wider environmental quality will only become apparent once a critical mass of roof space is greened (Grant, Engleback, & Nicholson, 2003). This was proven in a 2009 study of a business park in the Netherlands. A series of small green roofs were investigated as a potential means to negate their individual size limitation. (Snepa, Van Ierland, & Opdama, 2009). Green Roofs and Heat Island Effect/Urban Air Quality/Carbon Sequestering The surface temperatures of green roofs are significantly less than those of conventional roofs during summer. Studies have shown that if a large area of a city’s roofs are greened they can reduce the ‘heat island effect’ (Skinner, 2006; Alexandri & Jones, 2008). This is the principle reason for development of green roofs in cities such as Tokyo (Tokyo Metropolitan Government, 2002) and Chicago (City of Chicago, 2010). This effect is due to a reduced heat
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During a Penn State 2003 study, the temperatures on both green and standard roofs were measured. Both kinds of roofs warmed during the day and cooled overnight. While standard roofs cooled slightly more overnight, they warmed significantly more during the day. At their warmest, the standard roofs reached roughly 70oC, whereas the green roofs only reached about 40oC. (Gaffin, 2006).
reflectance from the surface of green roofs (Szokolay, 2008) and lower air temperatures as a result of the expiration of the planting (Skinner, 2006; Alexandri & Jones, 2008). The ability of combining the respiration of plants to a building’s structure also directly influences the air quality and CO2 content of the surrounding urban area. The combined area of leaves from the numerous plant species found on typical green roofs creates a large surface area capable of filtering out dust, pollutants and some forms of airborne viruses (Doernach, 1979; Brookes, 1984). Furthermore, there is growing evidence for the capacity of green roofs to act as carbon stores. Studies conducted on extensive green roofs in Michigan and Maryland found that they were actively sequestering 375gC/m2 (Getter, Rowe, Robertson, Cregg, & Andresen, 2009). Green Roofs and Rainwater Retention The water retention rate of green roofs is one of the most researched aspects of green roofs and is one of the documented reasons for Berlin developing green roofs (Earth Pledge, 2005). Lightweight moss and heather roofs have a retention rate of 18L/m² (Optigreen, 2011), and a grass roof can hold 30-80L/m² (Optigreen, 2011). Green roofs also reduce the immediate discharge of rainwater to 25% that of conventional roofs (Kӧhler, 1989). 07 Green Roofs’ effect on People While this report is concentrated on issues regarding the biological effects of green roofs, they also have a psychological and physiological impact on people. Numerous studies in hospitals (such as St. Luke’s Science Centre in Japan) have shown a link between the calming effects of plants and shortened patients’ recovery times (Earth Pledge, 2005). The introduction of planting to a building’s roof will reduce pollutants, dust particles and increase the humidity of air, which has been proven to enhance people’s mood and physical responsiveness (Crowther, 1994). They have also been proven to reduce employee absenteeism as a result of “healthier” buildings (Keeping, 1996). A study of employee satisfaction in buildings with access to a green roof in the Netherlands found that the majority of employees used (89%) and appreciated (92%) the space (Jókövi, Bervaes, & Böttcher, 2002). There are more subtle psychological benefits of green roofs, for example the increase presence of wildlife can be beneficial to people, especially to those in office blocks who regularly feel a disconnection with the outside world (Coppin, 1990; Natural Economy Northwest, 2008). 08 International Approaches to Rooftop Greening The potential value of green roofs in urban centres has not gone unnoticed by policy makers around the world. With their benefits towards the heat island effect (Skinner, 2006; Alexandri & Jones, 2008), runoff (Graceson, Hare, Hall, & Monaghan, 2011; Keeley, 2003) and ecology (Dunnett & Kingsbury, 2008), numerous local authorities are accommodating for and actively promoting green roofs in their legislation.
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Due to the extensive body of research undertaken by Dr Stephan Brenneisen in Basel, the city has amended its building and construction laws. As part of the city's biodiversity strategy, green roofs are now mandatory on all new buildings with flat roofs (Brenneisen S. , 2006). Also, if new green roofs exceed 500m2, their substrates must then be composed of natural soils and accommodate vegetation which comes from the surrounding region (Brenneisen S. , 2005). The London 2012 Olympics constructed 0.4ha (4,000m2) of green roofs on selected buildings as part of its Biodiversity Action Plan (Olympic Delivery Authority, 2008). And in Japan, green roofs are favoured by developers as a means to increase the retail value of their properties by an averaging 8% (CABE, 2005). However, the most comprehensive standards for green roof growing medias can currently be found in Germany (FLL, 2002).The German guidelines are regularly used by the green roofing industry throughout Europe, as they provide excellent information on vegetation growing conditions, water retention requirements and load capacity (FLL, 2002). These benchmarks have been built-up over the past number of decades, as many parts of Germany have a widespread adoption of green Image 12 - Ufa-Fabrik Centre, Berlin-Templehof roofs. For example during 2001, 14% of all new flat roofs constructed in Germany were green roofs, accounting for 13,500,000m2 as part of national and regional environmental legislation (Earth Pledge, 2005). 09 Potential for Habitat Green Roof in Ireland The purpose of this report was to investigate the potential of green roofs to address habitat loss in Ireland. The overall number of completed green roofs in Ireland is low. The concept of using green roofs to reinforce local ecology has been tried and tested in numerous studies in multiple cities (Brenneisen S. , 2006; Frith & Gedge, 2000). The examples of the Laban Dance Centre in London and the Moos Water Filtration Plant near Zurich have shown the readiness for both native flora and fauna species to be both supported by and enhanced by green roofs through active colonization (Clement & Foster, 1994; Frith & Gedge, 2000). The natural habitats associated with Coastal, Heathland and Grassland environments are the biological networks that present the most opportunity for the adoption to a rooftop situation in Ireland. Coastal Habitats
Grassland Habitats
Heathland Habitats
Image 13 - Costal Meadow grasses planted on the Nassau Icehouse Brewery
Image 14 - Grass sloped roof on the Vancouver Conference Centre
Image 15 - Heath Planting on Sloped Roof at Schiphol Plaza, Amsterdam Airport
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Coastal and Heather habitats are capable of existing on extremely lightweight structures with grassland habitats requiring lightweight to medium strength structure depending on the type of soil substrates required (Adler, 1999; Dunnett & Kingsbury, Planting Green Roofs and Living Walls, 2008). Similarly, the financial costs of Coastal and Heather habitats are extremely low and grasslands being low to medium in the spectrum of building expenditures (Earth Pledge, 2005). The three habitat types described represent the most effective habitats to be implemented on the majority of green roof conversion projects in Ireland. The green roof examples (Snepa, Van Ierland, & Opdama, 2009; Grant, 2006) within Basil, Berlin and Canary Wharf (Brenneisen S. , 2006; Earth Pledge, 2005) have shown that urban expansion can be integrated with ecologically considered greening mechanisms. Additionally, studies have proven that adding extensive green roofs on industrial and commercial land on the outskirts of residential areas can greatly improve the ecological resources in an urban area (Brenneisen S. , 2006). The size restriction of habitat green roofs is one of their primary limiting factors (Brenneisen & Hänggi, 2006). The close proximity of building and common development period presents opportunities for a mosaic of habitat green roofs to be created on industrial parks (Snepa, Van Ierland, & Opdama, 2009). Previous research has shown that the combination of small green roofs to create habitat corridors will significantly contribution to wider environmental quality (Grant, Engleback, & Nicholson, 2003). These factors further reinforce the ability of Coastal, Heathland and Grassland habitats to become a potential part of Ireland’s urban environments.
10 Concluding Statement The goal of this report was to ascertain if green roofs could play a role in addressing habitat loss in Ireland While arguments can be made for the ability of green roofs to sustain replicate habitats of Woodland and Wetlands districts, the potential of Coastal, Heathland and Grassland environments to be applied to existing structures across Ireland elevates these habitats as the principle candidates for habitat reconstruction in urban areas. Additionally the opportunity of green roofs in Ireland to provide safe breeding ground for internationally important bird populations is a valid reason in itself to promote green roof adoption. However, without some form of government support, either in the form of grants or favourable building policies, the wide scale implementation of a habitat focused green roofs will find a limited appeal with the Ireland’s populace. A study commissioned by English Nature, published in 2003, concluded that “Although individual green roofs offer local environmental benefits, any significant contribution to wider environmental quality is only likely to become apparent once a more substantial area of town and city roof space has been greened. Such a programme will require political commitment and concerted action underpinned by science, technical expertise and good design. In order to refine the design of green roofs for biodiversity conservation, some further research and experimentation is required.” (Grant, Engleback, & Nicholson, 2003) In conclusion, this statement accurately describes the current status of green roofs in Ireland.
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Ireland and Green Roof Habitat Recreation
The following table illustrates the connections between the habitats capable of surviving on green roofs and the requirements of natural habitats in Ireland.
Habitats favoured by Green Roofs
Coastal Vegetation
Ireland habitats capable of adapting to Green Roofs
Tidal Marine Habitats Saline Lagoon
Habitats Commonly Recreated on Green Roofs
Habitats Promoted by Ease of Construction and Financing
Coastal Habitats
Coastal Habitats Sand Dunes Vegetated Shingles Banks
Arid Vegetation
Cliffs and Slopes
Wetland Habitats Reed Beds
Wetland Habitats
Coastal Habitats
Floodplain Grazing Marsh
Reed Bed Vegetation
Woodland Habitats Wet Woodlands Mixed Ashwood Oakwood
Mountainous Vegetation
Grassland Habitats
Woodland Habitats
Grassland Habitats
Lowland Dry Acid Grassland Calcareous Grassland Lowland Meadow Purple Moor & Rush Pasture Limestone Pavement
Limestone Vegetation
Heathland Habitats
Grassland Habitats
Lowland Heaths Upland Heaths
Heathland Habitats
Mountainous Heaths
Shrub & Heath Vegetation
Peatland Habitats Lowland Raised Bog Blanket Bog
Heathland Habitats
Fens
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