Do looks matter? A case study on extensive green roofs using discrete choice experiments

Extensive green roofs are a promising type of urban green that can play an important role in climate proofing and ultimately in the sustainability of our cities. Despite their increasingly widespread application and the growing scientific interest in extensive green roofs, their aesthetics have received limited scientific attention. Furthermore, several functional issues occur, as weedy species can colonize the roof, and extreme roof conditions can lead to gaps in the vegetation. Apart from altering the function of a green roof, we also expect these issues to influence the perception of extensive green roofs, possibly affecting their acceptance and application. We therefore assessed the preferences of a self-selected convenience sample of 155 Flemish respondents for visual aspects using a discrete choice experiment. This approach, combined with current knowledge on the psychological aspects of green roof visuals, allowed us to quantify extensive green roof preferences. Our results indicate that vegetation gaps and weedy species, together with a diverse vegetation have a considerable impact on green roof perception. Gaps were the single most important attribute, indicated by a relative importance of ca. 53%, with cost coming in at a close second at ca. 46%. Overall, this study explores the applicability of a stated preference technique to assess an often overlooked aspect of extensive green roofs. It thereby provides a foundation for further research aimed at generating practical recommendations for green roof construction and maintenance

Independent Validation of the SWMM Green Roof Module

Green roofs are a popular Sustainable Drainage Systems (SuDS) technology. They provide multiple benefits, amongst which the retention of rainfall and detention of runoff are of particular interest to stormwater engineers. The hydrological performance of green roofs has been represented in various models, including the Storm Water Management Model (SWMM). The latest version of SWMM includes a new LID green roof module, which makes it possible to model the hydrological performance of a green roof by directly defining the physical parameters of a green roof’s three layers. However, to date, no study has validated the capability of this module for representing the hydrological performance of an extensive green roof in response to actual rainfall events. In this study, data from a previously-monitored extensive green roof test bed has been utilised to validate the SWMM green roof module for both long-term (173 events over a year) and short-term (per-event) simulations. With only 0.357% difference between measured and modelled annual retention, the uncalibrated model provided good estimates of total annual retention, but the modelled runoff depths deviated significantly from the measured data at certain times (particularly during summer) in the year. Retention results improved (with the difference between modelled and measured annual retention decreasing to 0.169% and the Nash-Sutcliffe Model Efficiency (NSME) coefficient for per-event rainfall depth reaching 0.948) when reductions in actual evapotranspiration due to reduced substrate moisture availability during prolonged dry conditions were used to provide revised estimates of monthly ET. However, this aspect of the model’s performance is ultimately limited by the failure to account for the influence of substrate moisture on actual ET rates. With significant differences existing between measured and simulated runoff and NSME coefficients of below 0.5, the uncalibrated model failed to provide reasonable predictions of the green roof’s detention performance, although this was significantly improved through calibration. To precisely model the hydrological behaviour of an extensive green roof with a plastic board drainage layer, some of the modelling structures in SWMM green roof module require further refinement

Thermal Performance of the Extensive Green Roofs in Hot Dry Climate

Green roofs have been used as an environmentally friendly product to encourage sustainable construction. Green roofs have a variety of advantages, such as reducing the energy consumption for cooling systems. The performance of these systems depends on the climates. The energy consumption for heating and cooling inside the residential and commercial buildings reach to 70% in hot dry climates such as Riyadh city which the temperature reached 50°C. So, the study aim to examine the efficiency of Extensive Green Roof system for reducing energy consumption of cooling in buildings in hot dry regions by compared it is performance with concrete roof system. The experimental validations were applied on residential building in Riyadh city during the summer season in 2014. The study used two rooms for testing thermal performance - the first room with extensive green roof system and the second room with concrete roof system. The results showed that using environmentally friendly insulation (Extensive Green Roof System) could reduce 12% to 33% for energy consumption of air conditioning in hot dry climates

Soil microarthropod community dynamics in extensive green roofs

Green roofs are of increasing interest to ecologists, engineers and architects, as cities grow and aim to become more sustainable. They could be exploited to improve urban biodiversity and ecosystem services, yet almost nothing is known about them from a soil community ecology perspective, despite how critical soil food webs are to ecosystem functioning. This paper provides the first comprehensive study incorporating the annual cycle of green roof soil microarthropods.Microarthropod communities were monitored over 14 months on two extensive green roofs. Abiotic factors, including substrate moisture, were recorded, as were biotic factors such as plant and mycorrhizal colonisation. Microarthropod interactions with these variables were then examined.Microarthropod diversity was low overall, with a few dominant species peaking seasonally. On occasion, total abundance was comparable to other early successional soils. The majority of species present were drought tolerant collembola and xerophillic mites, suggesting that moisture levels on green roofs are a major limiting factor for soil microarthropods.Our results suggest that the microarthropod community present in extensive green roof soils is impoverished, limiting the success of above-ground flora and fauna and ultimately the success of the roof as an urban habitat. We conclude that green roof building guidelines should incorporate soil communities in their design and should aim to be heterogeneous at the roof and landscape level, for the purpose of supporting soil biodiversity and creating sustainable habitats

Remarkable 3-in-1 Pakis-Stem Green Roofs for Saving Thermal Flat Rooftop

The green councils in the world are often promoting green buildings in terms of energy savings by mitigating the thermal load on buildings,especially thermal rooftop, into the room. Green roofs can be the most effective to lower roof thermal in tropical regions, but complicated and costly to build a perfect green roof even for a simple extensive green rooftop. This research looks for a remarkable growing medium for constructing green roof. Pakis-stem blocks can perform a 3-in-1 function: as a light-weight growing medium for green rooftops, an easy-to-form urban farming in private buildings or residences, and an eco-friendly external roof insulation. After a deep measurement on the rooftop surface and room thermal behaviour, the pakis-stem green rooftop can reduce 16.4oC of surface dry-bulk temperature and approximately 7oC ambient room dry-bulk temperature lower compared to conventional rooftops at noon. Furthermore, the surface temperature and ambient room air temperature difference between Pakis vegetative green rooftops and miana scrub green rooftop is approximately 7oC and 3oC respectively

Increasing Evapotranspiration on Extensive Green Roofs by Changing Substrate Depths, Construction, and Additional Irrigation

Urban environments are characterized by dense development and paved ground with reduced evapotranspiration rates. These areas store sensible and latent heat, providing the base for typical urban heat island effects. Green roof installations are one possible strategy to reintroduce evaporative surfaces into cities. If green roofs are irrigated, they can contribute to urban water management and evapotranspiration can be enhanced. As part of two research projects, lysimeter measurements were used to determine the real evapotranspiration rates on the research roof of the University of Applied Sciences in Neubrandenburg, Germany. In this paper, we address the results from 2017, a humid and cool summer, and 2018, a century summer with the highest temperatures and dryness over a long period of time, measured in Northeast Germany. The lysimeter measurements varied between the normal green roof layer (variation of extensive green roof constructions) and a special construction with an extra retention layer and damming. The results show that the average daily evapotranspiration rates can be enhanced from 3 to 5 L/m2/day under optimized conditions. A second test on a real green roof with irrigation was used to explain the cooling effects of the surface above a café building in Berlin

Teaching old buildings new tricks: benefits of retrofitting Indianapolis buildings with green roofs

Not your basic rooftop garden, green roofs contain growing media and are planted with various types of vegetation. Green roofs can be either intensive, with soil depths above 6 inches and increased size and attractiveness of vegetation, such as trees and shrubs, or extensive, with soil depths between 2-6 inches and low, moss or grass-like plants that require little care (Getter et al. 2009, Indianapolis DPW 2008, Obemdorfer et al. 2007, US DOE 2004). Although green roofs are initially more expensive than traditional roofing techniques due to the cost of additional materials, the long-term cost savings are high and can provide a retum on investment (Carter and Keeler 2008, Indianapolis DPW 2008, US DOE 2004). With the growing popularity of green roofs in the United States, these costs are going down. In Germany, where green roof technology has been established for 30 years, prices for green roof construction are as low as 50% that of conventional roofs (www.greenroofs.com). Several cities, especially in Europe, are adopting regulations for the incorporation of green roofs onto portions of their buildings. In Basel, Switzerland, research on the biological conservation potential of green roofs has contributed to the 3 city\u27s new strategy of mandating the installation of green roofs on all new buildings with flat roofs (Brenneisen 2006). Retrofitting an existing structure with a green roof is also an increasingly common approach. Flat roofs are generally the best candidates for this construction because they often do not necessitate additional support for the low extra weight of an extensive green roof, and they require little expertise in their installation (Carter and Keeler 2008). A good candidate roof for retrofit installation should be expected to hold an extra 15-25 pounds per square foot (psf) (Indianapolis DPW 2008). Rock ballast roofs generally weigh 10-15 psf, and would be replaced with an extensive green roof that could weigh 10-35 psf saturated (Indianapolis DPW 2008). If changes to the roof structure are necessary, these can include additional decking, roof trusses, or joists (Indianapolis DPW 2008). Incorporating a green roof onto any building provides a multitude of environmental and economic benefits, such as lowered heating and cooling costs, carbon sequestration, decreased air and noise pollution, reduced urban heat island effects, stormwater management, increased lifetime of roof membrane, presence of a more aesthetically pleasing area, and increased urban biodiversity (Getter et al. 2009, Obemdorfer et al. 2007, Altor 2010)

Considerations for plant selection in green roofs

It is the vegetation layer that creates the living skin on the rooftop in green roofs, controls the long-term effect of any green roof installation and provides a naturally evolving and changing roofscape. Therefore, plant layer is the most challenging and important element of green roofs. A successful green roof system needs a meticulous plant selection. Considering aesthetic values, different designs are available which incorporate various plant species, but the vegetative layer requires wise consideration in terms of the projected goals and existing conditions. Design goals of the roof define the plant selection process, whether the goals are linked to aesthetic values, performance, education or function. Like any landscape at ground level, vegetative layer that propagate primarily on a green roof may not continue to flourish in the long term as a result of fluctuation in climate and other critical factors. While, aesthetic values and ecological aspects are crucial criteria in roofscape, the selected plants must first be survivable. The plant selection process relies on the building structure, aesthetic values, micro-climate condition, existing maintenance and the condition of growing medium. Necessarily, green roof vegetation must be less nutrient-reliant and tougher than plant species currently found in ground level landscape. In this case Crassulacean acid metabolism (CAM) plants are suggested. In Overall, the best plants for green roofs environment are cold, heat, drought, wind, sun, disease and insect tolerant and preferably native plant species. Drought resistant, durable and low maintenance plant species are recommended for extensive green roofs; however, almost infinite plant selection is used for intensive green roofs

An insight into the commercial viability of green roofs in Australia

Construction industries around the world have, in recent history, become increasingly concerned with the sustainability of building practices. Inherently, the development of the built environment results in partial or complete destruction of the natural environment. Advanced European and North American countries have turned to green roofs as a means of sustainable development. Australia, on the other hand, has yet to fully realize the potential of green roof technology. In the first case, an extensive review of green roof literature was undertaken to establish the dominant perspectives and over-riding themes within the established body of international literature. The collection of primary data took the form of qualitative, semi-structured interviews with a range of construction practitioners and green roof experts; landscape architects, consultants and academics. The information gained from the interviews facilitated the primary aim of the paper; to critically analyse the state-of-practice in the Australian green roof industry. Green roofs, despite their proven sustainability benefits and their international success, have experienced a relatively sluggish uptake in the Australian construction industry. With this being said, the Australian green roof industry is considered to have promising potential for the future; should there be legislative changes made in its favour or greater education within the industry. To advance the local industry, it was found that government authorities are required to adapt policy settings to better encourage the use of green roofs, whilst industry bodies are required to host better, more targeted educational programs

Green Roofs Support a Wide Diversity of Collembola in Urban Portland, Oregon

Green roofs can help address habitat loss in urban areas by supporting plant and animal communities. To determine whether green roofs can support collembola biodiversity, we collected pitfall samples from April-June 2015 on two extensive and two intensive green roofs in urban Portland, Oregon. Twenty morphospecies were found across the roofs, indicating that green roofs support a diversity of collembola taxa. The intensive roofs were more biodiverse than the extensive, though roof type may not be the most significant factor affecting collembolan biodiversity. Each of the four green roofs were characterized by a different and unique most dominant morphospecies, and, indeed, each roof possessed a different set of top-three abundant collembola taxa. While green roofs support moderate collembola diversity, preserving natural habitat is important to maintain species richness