Green roofs are gaining in popularity around the country and are used to create healthy, ecologically responsible buildings. They improve a building’s performance and support living vegetation on a flat or pitched surface.

Green roofs can extend the lifespan of a roof by protecting the waterproofing layer from weather and temperature changes. They can provide sound insulation, reduce the heating and cooling requirements and slow stormwater runoff, alleviate the urban heat island effects, capture gaseous and particulate pollutants and improve air quality. The structures can support local biodiversity, create a new open space for recreation, growing food and support the inhabitants’ physical and mental health.

Green roofs have come a long way since the Viking and Middle Ages when most houses in Scandinavia had “sod roofs”. Modern green roofs have been gaining momentum across the globe since marketed on a large scale in the early seventies in Germany.

The first consideration when building a green roof is the weight and purpose. In general there are a few types of green roofs. Extensive green roofs have a thin growing medium while intensive green roofs have deeper soil and are much heavier.

Extensive green roofs are shallow and can provide the environmental benefits of a green roof, but cannot support regular foot traffic. Extensive green roofs have a growing medium of less than 200mm and a roof structure similar to conventional roof coverings. They weigh between 60–200kg/sqm and are relatively economical. They can support less water and root growth, grow a limited variety of more hardy plant options. They provide thermal and acoustic insulation benefits and are relatively easy to retrofit on existing roofs.

Intensive green roofs are the big-brother of extensive green roofs. They have a larger profile of up to 1m deep, allowing them to support larger plants and have a greater water-holding capacity. They can weigh between 180-500kg/sqm or more and require a stronger physical roof structure. This makes them a more expensive option but they have a wider scope for design and use. They have greater thermal and acoustic insulation benefits but are difficult to retrofit existing buildings.

In between extensive and intensive are semi-intensive green roofs, which are grown 120mm to 180mm high with perennials, small shrubs, and ornamental grasses. They do not contain tall-growing bushes or trees. Semi-intensive green roofs have moderate watering and maintenance needs and are suited for roofs that can support 65 to 115kg per square meter of load. They function as stormwater filters and habitat for urban wildlife.

There are also monolithic and modular green roofs. A monolithic green roof is one where all components are placed on the roof in layers and plant roots are free to intertwine with those of adjacent plants all across the roof. A modular green roof system, on the other hand, is made up of multiple containers or green roof trays. These trays contain all the components of a green roof, such as drainage, root containment, growing media, and plants.

A typical green roof has seven layers on top of the structural components. It starts with a waterproofing membrane, which is commonly followed by a root barrier layer, an optional layer of insulation, drainage layer, filter fabric, growing medium and finally, vegetation.
green roof native plants
Green Roof Standards
Viewed from the surface, green roofs appear to be natural. However, the material beneath the plants is typically composed of an engineered growing medium. The medium is high in minerals and low in organic matter. Research on the best growing media for green roofs was pioneered in Germany and Switzerland. In the 1970s, a group of German researchers developed the FLL German Guidelines for Rooftop Greening, which aided those developing, designing, and constructing vegetated roofs.

When Creating The Growing Medium For A Green Roof Designers Need To Consider:
the composition of the medium
its drainage characteristics
the fertility requirements of plants

Always check with local building code offices before beginning a green roof construction process. One of the most important considerations will be the load-bearing capacity of the existing roof. Local building code offices will have information on how to check the structural requirements of your green roof design. In most cases, a building permit must be obtained to begin and carry out a green roof project. Check with your local building code office for more information.
green roofs South Africa
1. A waterproofing membrane
There are serveal major categories of waterproofing membranes: tourch-on, liquid applied membrane treatments, preformed sheets, including ‘single ply’ and integrated systems.

Liquid applied membrane material can be made from bitumen emulsions, modified bitumen, polymer cement systems, polyurethane, polyurethane modified acrylic, acrylic or two-part polyurethane hybrid elastomers. The material is in a liquid state, is applied manually and is suitable for small roofs or roofs with a number of upstands, penetrations, corners or steep slopes. Liquid applied membranes are easy to apply, tolerant to surface imperfections, easily repaired or reapplied and are seamless. However, they are not root resistant, it is difficult to ensure uniformity of thickness, they may become brittle if exposed to sunlight and high temperatures.

A preformed membrane suits larger, flat or gently sloping roofs. The majority are either asphalt-based or polymer-based and are either loose-laid or fully bonded to the substrate. They have a uniform thickness and asphalt base systems are torched down and seam welded for additional sealing and strength but are not usually trafficable, UV stable or root resistant. PVC membranes and Ethylene Propylene Diene (EPDM) and Butanoyl membranes are root resistant and Thermosetting and Thermoplastics are UV stable. Preformed membranes require a high level of skill for installation and there is the possibility condensation or moisture may soften the glue or adhesive tapes along the seams and bonding.

To create an integrated system, additives are included in the concrete mix to waterproof the concrete. They are used for larger concrete structures such as landscaping over car parks or on car parking buildings.

2. Root barrier layer
The root barrier layer protects the waterproofing membrane from damage caused by plant roots. It may not be necessary if a root-resistant waterproofing membrane is used. Typical materials used are polyethylene (plastic) sheets and polypropylene geotextile fabric. Ensure the root barrier sheet is compatible with the waterproofing membrane so no adverse reaction or chemical action occurs.

3. Insulation (optional)
Green roofs provide significant thermal insulation but since it is difficult to obtain accredited insulation values for green roof construction, it may be necessary to use conventional means of insulation to meet the BCA’s thermal insulation standards.

4. Drainage layer
A drainage layer carries away excess water and should strike a balance between storing water in the soil and draining storm water.

Plastic drainage sheets or boards are common drainage materials for greenroofs and are installed as a continuous layer. Plastic drainage layers may be rigid, open mesh structures or they may have a cup style design, enabling water to be stored at the base and used later by the plant. Cup-style drainage sheets should be overlapped to eliminate gaps between sheets while other plastic drainage types should have adjacent sheets butted together. For green roofs with high traffic, install rigid draining layers to avoid compression.

5. Filter fabric
Laid on top of the drainage layer is a filter fabric made of geotextile materials such as fleece or other woven materials. This layer holds the soil in place and separates the drainage layer from the growing medium, preventing the growing medium from blocking the drainage layer or stormwater system.

6. Growing medium
Next up is the growing medium, which is manufactured soil, inorganic material which may be supplemented with organic material such as coconut fibre or coir. Using a mixture of native soil and organic or mineral additives can help with water retention, permeability, density and erosion control. As a general guide, the growing medium should be 75-80 per cent inorganic material such as expanded slate or crushed clay and 20-25 per cent organic material such as humus and clean soil. This will provide drainage and soil air capacity, and nutrients for the plants.

7. Vegetation
The final layer is the vegetation. Extensive green roofs require low maintenance vegetation and many native plants from coastal and arid inland regions are suitable. Intensive green roof plants can be treated in a similar way to ground level gardens and require the same level of maintenance, but native plants are preferred.
greenroofs native plants
Plants suitable for extensive green roofs include low growing succulents and herbaceous perennials originating from dryland habitats. Annual to biennial plants can be used successfully on green roofs and tend to fall into the groups of quick growing annuals and ephemerals. Members of the Sedum family, which consists of 600 types of succulents are a safe choice.

Intensive green roofs with substrate deeper than 250mm can also support small shrubs and turf. Sports turf requires a designed soil or growing medium to ensure effective drainage and regular irrigation, fertilising and mowing. Vegetables require irrigation and a substrate depth of at least 200mm.

Substrate deeper than 500mm can grow shrubs up to two metres but plants with dense, upright habits should only be used where there is minimal wind exposure.

Substrate deeper than 1m can support small trees up to five metres. Trees with sparse canopies, flexible stems and high tolerance to heat are best in areas of high wind exposure.
green roofs South AfricaGREEN ROOF RESEARCH NOTES

Sustainable Garden Roofs Developed As New Construction Material
Plataforma SINC

A Spanish research study has tested different combinations of supports and indigenous plants to determine which are the best for reducing energy consumption inside buildings. This type of roof is a “rurban,” sustainable architectural solution that will lead to a reduction in environmental and acoustic contamination levels in cities, and be visually pleasing.

Researchers from the Polytechnic University of Madrid (UPM) have built a roof covered with plants and a watering system that will optimise the consumption of a building’s heating and cooling systems thanks to its insulation. It is a third-generation ecological roof, characterised by its sustainability and the use of indigenous plant species.

The Impact Of Green Areas On Mitigating Urban Heat Island Effect: a review
Nastaran Shishegar - University of Illinois, Urbana-Champaign

Published in 2014 Urban Heat Island (UHI) is one of the major problems in the 21st century as a consequence of urbanisation and industrialisation of human civilisation. The main source of UHI is the considerable amount of heat produced from urban structures, as they absorb and re-radiate solar radiations. Therefore, urban heat islands develop in areas with a high percentage of non-reflective, water-resistant surfaces and a low percentage of vegetation. Specifically, a lack of vegetation reduces heat lost due to evapotranspiration. Vegetation, particularly in the presence of high moisture levels, plays a vital role in the regulation of surface temperatures, even more than may non- reflective or low-albedo surfaces. There are different ways of reducing the effects of UHI. However, a common measure to mitigate urban heat island is to increase urban green spaces such as parks, street trees and green roofs. This paper discusses the current literature and knowledge about the impacts of green spaces on mitigating UHI. Studies conducted on the influence of greenery on mitigating UHI have indicated that all green spaces help urban areas adapt to the impact of UHI regardless of whether they are parks, street trees or green roofs.

Green Roofs As Urban Ecosystems: Ecological Structures, Functions And Services
Erika Oberndorfer, Brad Bass - Environment Canada, Jeremy T. Lundholm - Saint Mary's University, Reid Coffman - Kent State University, Hitesh Doshi, Stuart Gaffin - Columbia University, Karen K.Y Liu, Nigel Dunnett - The University of Sheffield, Manfred Köhler - Hochschule Neubrandenburg, D. Bradley Rowe - Michigan State University

Green roofs (roofs with a vegetated surface and substrate) provide ecosystem services in urban areas, including improved storm-water management, better regulation of building temperatures, reduced urban heat-island effects, and increased urban wildlife habitat. This article reviews the evidence for these benefits and examines the biotic and abiotic components that contribute to overall ecosystem services. We emphasize the potential for improving green-roof function by understanding the interactions between its ecosystem elements, especially the relationships among growing media, soil biota, and vegetation, and the interactions between community structure and ecosystem functioning. Further research into green-roof technology should assess the efficacy of green roofs compared to other technologies with similar ends, and ultimately focus on estimates of aggregate benefits at landscape scales and on more holistic cost-benefit analyses

Direct and Indirect Impacts of Vegetation On Building Comfort: A Comparative Study of Lawns, Green Walls and Green Roofs
Laurent Malys, Christian Inard - Université de La Rochelle, Marjorie Musy - Centre d’études et d’expertise sur les risques, l’environnement, la mobilité et l’aménagement

Following development and validation of the SOLENE-microclimat tool, the underlying model was used to compare the impacts of various "greening strategies" on buildings' summer energy consumption and indoor comfort. This study distinguishes between direct and indirect impacts by successively implementing the test strategies on both the studied building and surrounding ones; it also considers insulated vs. non-insulated buildings. Findings indicate that green walls have a direct effect on indoor comfort throughout the entire building, whereas the effect of green roofs is apparently primarily confined to the upper floor. Moreover, the indirect effect of a green wall is greater, mainly due to the drop in infrared emissions resulting from a lower surface temperature. It has also been proven that the indirect effects of green walls and surrounding lawns can help reduce the loads acting on a non-insulated building.

Residential Green Space In Childhood Is Associated With Lower Risk Of Psychiatric Disorders From Adolescence Into Adulthood
Kristine Engemann, Carsten Bøcker Pedersen, Lars Arge, Constantinos Tsirogiannis, Preben Bo Mortensen, and Jens-Christian Svenning

Urban residence is associated with a higher risk of some psychiatric disorders, but the underlying drivers remain unknown. There is increasing evidence that the level of exposure to natural environments impacts mental health, but few large-scale epidemiological studies have assessed the general existence and importance of such associations. Here, we investigate the prospective association between green space and mental health in the Danish population. Green space presence was assessed at the individual level using high-resolution satellite data to calculate the normalized difference vegetation index within a 210 × 210 m square around each person’s place of residence (∼1 million people) from birth to the age of 10. We show that high levels of green space presence during childhood are associated with lower risk of a wide spectrum of psychiatric disorders later in life. Risk for subsequent mental illness for those who lived with the lowest level of green space during childhood was up to 55% higher across various disorders compared with those who lived with the highest level of green space. The association remained even after adjusting for urbanization, socioeconomic factors, parental history of mental illness, and parental age. Stronger association of cumulative green space presence during childhood compared with single-year green space presence suggests that presence throughout childhood is important. Our results show that green space during childhood is associated with better mental health, supporting efforts to better integrate natural environments into urban planning and childhood life.

Estimating The Environmental Effects Of Green Roofs
A case study in Kansas City, Missouri

A green roof, also called a vegetated roof or eco-roof is a roof with soil and plants placed on top of a conventional roof. Green roofs are growing in popularity, as they have proven to be a cost-effective strategy for creating more livable and sustainable cities.1 Integrating nature-based solutions like green roofs into the urban landscape can benefit the environment, public health, and society by:

Reducing stormwater runoff.
Lowering ambient air and surface temperatures and reducing the urban heat island effect.2,3
Increasing building efficiency and reducing energy use for heating and cooling.4
Reducing air pollution associated with heating, electric power generation, and temperaturedependent formation of ground-level ozone.5
Achieving health benefits associated with reducing fine particulate matter (PM2.5) air pollution.
Improving psychological well-being through access to nature.6
This case study uses the Kansas City metropolitan area, and specifically the city of Kansas City, Missouri (KCMO), to demonstrate the environmental and health benefits of green roofs. Companies and municipalities are increasingly turning to nature-based approaches like green infrastructure to help protect people and infrastructure from extreme temperatures, severe storms, and chronic droughts. For example, city planners and stormwater managers are implementing green roofs and other green infrastructure practices as a cost-effective way to manage stormwater where it falls, reducing polluted runoff and keeping excess stormwater out of the sewer system while also creating a community amenity. By 2020, green roofs in KCMO could retain 29 inches of annual stormwater runoff if building developers and parking garage owners continue to install green roofs at the current growth rate. The intended audiences of this case study are city planners, regional planning organizations, nonprofits, environmental staff in governors’ offices, and other state or local officials who want to learn about and be able to demonstrate that green roofs have multiple environmental benefits: providing stormwater management during wet weather events, lowering ambient air temperatures on hot summer days, and cleaning the air. This information may also be useful for stormwater management plans, for meeting National Pollutant Discharge Elimination System permitting requirements, or for Air Quality Management Plans, such as those that may be developed under EPA’s Ozone and Particulate Matter Advance Programs.

Benefits And Potential Applications Of Green Roof Systems In Hong Kong
Sam C M Hui, Technological and Higher Education Institute of Hong Kong - Department of Construction Technology and Engineering

Green roof systems are living vegetation installed on the roofs and could contribute positively to the mitigation of urban heat island and enhancement of building thermal and environmental performance. Research study has been carried out to investigate the green roof technology and research in the world, with the aim to develop practical information for its applications in Hong Kong and other similar urban cities. The important factors for assessing the performance and designing the systems have been evaluated. This research paper highlights the key findings of the evaluation and discusses the benefits and potential applications of the green roof systems.

Green Roof Stormwater Retention: Effects of Roof Surface, Slope, and Media Depth
Nicholaus D VanWoert, D. Bradley Rowe - Michigan State University, Jeff Andresen - Michigan State University, Clayton L Rugh

Urban areas generate considerably more stormwater runoff than natural areas of the same size due to a greater percentage of impervious surfaces that impede water infiltration. Roof surfaces account for a large portion of this impervious cover. Establishing vegetation on rooftops, known as green roofs, is one method of recovering lost green space that can aid in mitigating stormwater runoff. Two studies were performed using several roof platforms to quantify the effects of various treatments on stormwater retention. The first study used three different roof surface treatments to quantify differences in stormwater retention of a standard commercial roof with gravel ballast, an extensive green roof system without vegetation, and a typical extensive green roof with vegetation. Overall, mean percent rainfall retention ranged from 48.7% (gravel) to 82.8% (vegetated). The second study tested the influence of roof slope (2 and 6.5%) and green roof media depth (2.5, 4.0, and 6.0 cm) on stormwater retention. For all combined rain events, platforms at 2% slope with a 4-cm media depth had the greatest mean retention, 87%, although the difference from the other treatments was minimal. The combination of reduced slope and deeper media clearly reduced the total quantity of runoff. For both studies, vegetated green roof systems not only reduced the amount of stormwater runoff, they also extended its duration over a period of time beyond the actual rain event.

Green Roofs for Stormwater Runoff Control
Robert Berghage - Pennsylvania State University, David Beattie, Christine Thuring - The University of Sheffield

This project evaluated green roofs as a stormwater management tool. Specifically, runoff quantity and quality from green and flat asphalt roofs were compared. Evapotranspiration from planted green roofs and evaporation from unplanted media roofs were also compared. The influence of media type, media depth and drought during plant establishment on plant growth and long-term management of media pH were investigated. The goal of the project was to provide high-quality replicated data which could be used to develop and refine reliable anticipated runoff volumes and loadings from green roofs, respectively, as well as evaluate factors which impact plant growth and establishment. Results indicate that the green roofs are capable of removing 50% of the annual rainfall volume from a roof through retention and evapotranspiration. Rainfall not retained by green roofs is detained, effectively increasing the time to peak, and slowing peak flows for a watershed. There are seasonal considerations as more runoff is generated during winter and for many summer storms there was no runoff. Green roof runoff does contain concentrations of some nutrients and other parameters, but values are in line with other planted systems. Due to the volume reduction, actual nutrient loadings from green roofs are less than asphalt roofing runoff or otherwise manageable at the downspout.

Reducing Urban Heat Islands: Compendium of Strategies – Urban heat island basicsHashem Akbari, Ryan Bell, Tony Brazel, David Cole, Maury Estes, Gordon Heisler, David Hitchcock, Brenda Johnson, Megan Lewis, Greg McPherson, Tim Oke, Danny Parker, Alan Perrin, Joyce Rosenthal, David Sailor, Jason Samenow, Haider Taha, James Voogt, Darrell Winner, Kathy Wolf, Barry Zalph - Climate Protection Partnership Division in the U.S. Environmental Protection Agency’s Office of Atmospheric Programs

As urban areas develop, changes occur in the landscape. Buildings, roads, and other infrastructure replace open land and vegetation. Surfaces that were once permeable and moist generally become impermeable and dry. This development leads to - the formation of urban heat islands—the phenomenon whereby urban regions experience warmer temperatures than their rural surroundings.

CO2 Payoff Of Extensive Green Roofs With Different Vegetation Species
Takanori Kuronuma, Hitoshi Watanabe, Tatsuaki Ishihara, Daitoku Kou

Green roofs are considered effective in the reduction of atmospheric CO2 because of their ability to reduce energy consumption of buildings and sequester carbon in plants and substrates. However, green roof system components (substrate, water proofing membrane, etc.) may cause CO2 emissions during their life cycle. Therefore, to assess the CO2-payofffor extensive green roofs, we calculated CO2 payback time it takes their CO2 sequestration and reduction to offset the CO2 emitted during its production process and maintenance practices. The amount of CO2 emitted during the production of a modular green roof system was found to be 25.2 kg-CO2˙m⁻². The annual CO2 emission from the maintenance of green roofs was 0.33 kg-CO2˙m⁻²˙yr⁻¹. Annual CO2 sequestration by three grass species with irrigation treatment was about 2.5 kg-CO2˙m⁻²˙yr⁻¹, which was higher than that of Sedum aizoon. In the hypothetical green roofs, annual CO2 reduction due to saved energy was between 1.703 and 1.889 kg-CO2˙m⁻²˙yr⁻¹. From these results, we concluded that the CO2 payback time of the extensive green roofs was between 5.8 and 15.9 years, which indicates that extensive green roofs contribute to CO2 reduction within their lifespan.

Mitigation Solutions For GHG Emissions in New Construction
Vahidi, E., Kirchain, R., Gregory, J.

By 2050, the United States is projected to add 121 billion ft2 of buildings—equivalent to constructing New York City every year for the next 20 years. However, to meet climate change goals the U.S. building sector must also significantly reduce its greenhouse gas (GHG) emissions. In this brief, we investigate which GHG mitigation solutions could help meet these GHG targets even as the nation experiences such unprecedented construction.

Sustainable Building Material For Green Building Construction, Conservation & Refurbishing
Usman Aminu Umar - Universiti Teknologi PETRONAS, Dr. Mohd Faris Khamidi - Qatar University, Hassan Tukur

Materials are the essential components of buildings construction. Chemical, physical and mechanical Properties of materials as well as an appropriate design are accountable of the building mechanical strength. The design of green buildings should thus begin with the selection and use of eco-friendly materials with related or better features than traditional building materials. Building materials are usually selected through functional, technical and financial requirements. However, with sustainability as a crucial issue in the last decades, the building sector, directly or indirectly causing a considerable portion of the annual environmental deterioration, can take up the obligation to contribute to sustainable development by finding more environmentally benign methods of construction and building. Among the directions for solutions is to be found in new material applications, recycling and reuse, sustainable production of products or use of green resources, Careful selection of eco-friendly sustainable building materials may be the fastest way for builders to start integrating sustainable design concepts in buildings. Ordinarily, price has been the primary consideration when comparing related materials or materials selected for similar purpose. Nevertheless, the price of a building element signifies just the manufacturing and transportation costs, not social or environmental costs. Substantial initiatives have been carried out by the research community globally, in order to discover alternative sustainable building materials and low technology techniques, which result in a more sustainable and affordable construction complying with the comfort standards required today. Embracing green building materials is a good alternative to meet to this objective. Therefore, Selection of construction materials that have minimum environmental burdens is useful in the sustainable development of a nation. The purpose of this paper is to highlight how sustainable building material can contribute to lessen the impact of environmental degradation, and generate healthy buildings which can be sustainable to the occupant as well as our environment.

Towards Sustainable Building Design
David Grierson, University of Strathclyde

Work recently undertaken at the University of Strathclyde, Department of Architecture, is concerned with the articulation of a management system that might support sustainable design. Aligned with the international standard ISO 14001, a system has been piloted in housing development projects around Glasgow, and offers a supporting framework for the implementation of agreed actions and addresses a number of key urban planning and building design tasks incorporating six related themes. This paper will discuss the context and introduce the themes of Human Impact (including consideration of quality of life issues, consultation and social inclusion, development factors, health factors, comfort levels, accessibility, public transportation, facilities for cyclists); Environmental Impact (including consideration of protection of local ecological features/biodiversity, environmental assessment); Pol- lution Prevention (including consideration of indoor air quality (emissions from equipment, out- gassing of toxins/radiations), elimination of toxins, control of pollutants during constructions); Sus- tainability Management (including consideration of integrated and systemic approaches e.g. sustain- ability/environmental performance targets, management systems and procedures, construction man- agement, commissioning, dissemination workshops, post-occupancy feedback visits); Resource Efficiency (including consideration of, lean design, material use and recycling, embodied energy, water consump- tion and conservation); and Energy Efficiency (including consideration of, targets, benchmarks and best practice energy use, passive solar, renewable energy, thermal modelling, insulation, ventilation, heating, CHP, heat recovery.

New York City Property Values: What Is The Impact Of Green Roofs On Rental Pricing
Kiku Ichihara, Jeffrey P. Cohen - University of Connecticut, School of Business

Green roofs have recently seen increasing popularity in many cities, such as New York, due to their cooling effects, stormwater control features, and aesthetics and amenity values. Few known studies, however, have attempted to quantify the benefits of green roofs into monetary values. We use hedonic regression techniques to obtain estimates that apartment rents in buildings with green roofs in the Battery Park City area of New York were about 16% higher on average than in buildings without green roofs. Battery Park City is located in the Upper Bay Combined Sewer Overflow (CSO) watershed. If we were to extend the Battery Park City findings to the entire Upper Bay CSO watershed and if all buildings in the CSO watershed were to install green roofs, our results imply that rental receipts in the watershed could increase by as much as approximately $2.1 billion monthly.

Probabilistic Social Cost Benefit Analysis For Green Roofs: A Lifecycle Approach
Fabrício Silva Bianchini, Kasun Chandranath Hewage

Green roofs have been used as an environmentally friendly product for many centuries and considered as a sustainable construction practice. Economic and environmental benefits of green roofs are already proven by many researchers. However, a lifecycle net benefit-cost analysis, with the social dimension, is still missing. Sustainable development requires quantitative estimates of the costs and benefits of current green technologies to encourage their use. This paper is based on an extensive literature review in multiple fields and reasonable assumptions for unavailable data. The Net Present Value (NPV) per unit of area of a green roof was assessed by considering the social-cost benefits that green roofs generate over their lifecycle. Two main types of green roofs – i.e. extensive and intensive – were analyzed. Additionally, an experimental extensive green roof, which replaced roof layers with construction and demolition waste (C&D), was assessed. A probabilistic analysis was performed to estimate the personal and social NPV and payback period of green roofs. Additionally, a sensitivity analysis was also conducted. The analysis demonstrated that green roofs are short-term investments in terms of net returns. In general, installing green roofs is a low risk investment. Furthermore, the probability of profits out of this technology is much higher than the potential financial losses. It is evident that the inclusion of social costs and benefits of green roofs improves their value.

Experimental Investigation Of The Thermal Performances Of An Extensive Green Roof In The Mediterranean Area
Piero Bevilacqua - Department of Mechanical, Energy and Management Engineering, University of Calabria, Cosenza, Italy, Domenico Mazzeo - Department of Mechanical, Energy and Management Engineering, University of Calabria, Cosenza, Italy, Roberto Bruno - Department of Mechanical, Energy and Management Engineering, University of Calabria, Cosenza, Italy, Natale Arcuri - Department of Mechanical, Energy and Management Engineering, University of Calabria, Cosenza, Italy

Nowadays green roofs are a well-consolidated technology used in several countries since these systems can be employed both to generate considerable energy savings and to improve the thermal performances of buildings. This paper deals with an experimental analysis of an extensive green roof, installed on a building of the University of Calabria (Italy, Lat. 39.3◦ N). The thermal performances of different layering solutions are analysed under typical Mediterranean climate conditions with reference to a traditional roof system. The analysis showed that the green roof is able to reduce the temperature at the interface with the structural roof, on average, by 12 ◦C with respect to a black bituminous roof in summer and to maintain, onaverage, a value thatis 4 ◦Chigher in winter. Themeasured temperatures allowed to calculate the transferred heat through the building roof, showing negative heat fluxes for the whole period and a reduction ofthe thermal energy entering the indoor environment of 100% in summer, proving the passive cooling effect of the green roof, and a reduction between 30% and 37% of the thermal energy exiting the indoor environment in winter. The experimental data have been employed also to conduct a dynamic characterization of the different vegetated solutions, showing that the different green roofs solutions are able to generate values of decrement factor varying between 0.135 and 0.193 and a time lag between 3.1 h and 4.8 h, which can substantially improve the dynamic properties of traditional roof structures, especially in the case of roofs with limited dynamic performances.

Evidence For Improved Urban Flood Resilience By Sustainable Drainage Retrofit
Carly B. Rose, University of the West of England, Bristol, UK, Jessica E. Lamond, University of the West of England, Bristol, UK, Colin A. Booth, University of the West of England, Bristol, UK

The rapid growth of cities under modern development pressure has resulted in surface water flooding becoming an increasing hazard and future climate change uncertainties may exacerbate this threat still further: retrofitting sustainable drainage systems to attenuate stormwater runoff has been advocated as part of an integrated solution required to address this problem. Many of these adaptations not only enhance a community’s resilience to flooding, but may also offer additional benefits in terms of improved environmental amenity and quality of life. The evidence base for sustainable drainage is critically evaluated in respect of the implications for urban planning, as applied to existing housing stocks and business properties in urban areas worldwide. It is concluded that this approach can make a substantial contribution towards urban resilience as part of an integrated approach to managing extreme storms. This will be of interest to urban planners and designers considering the implementation of integrated flood risk management.

Better Ways To Manage Urban Stormwater Runoff
University of California - Irvine

As meteorologists monitor the El Nino condition currently gaining strength in the Pacific Ocean, Californians look with hope to the much-needed rain and snow it could yield. But if we're going to make the most of the precipitation, we need to put a LID on it. LIDs, or low-impact development technologies, mimic pre-urban stream functions. Examples are green roofs that absorb and evapotranspire rainfall; rainwater tanks attached to homes and other buildings; and permeable pavement for roads, driveways and parking lots. Rainwater could even be used in the home for toilet flushing and laundry. Managing stormwater runoff in urban environments is a challenge for engineers and water officials. During pre-industrial times, rainwater gradually seeped into the ground and, from there, into rivers, lakes and oceans. Humans, however, have replaced forests and grasslands with a lot of impermeable surfaces that send runoff in a torrent directly to the closest waterways. Symptoms include erosion, flooding and rising stream temperatures; an imbalance in nutrients, carbon and oxygen in the water; and an increase in unwanted sediments, chemical pollutants and human pathogens.

How To Reduce Extreme Heat In City Neighborhoods
Portland State University

Planting more vegetation, using reflective materials on hard surfaces and installing green roofs on buildings can help cool potentially deadly urban heat islands -- a phenomenon that exists in nearly all large cities -- a new study shows.

Led by Urban Studies and Planning Professor Vivek Shandas and published in the May 21 edition of the journal Atmosphere, the study used computer modeling to show the temperature differences that can be made in a variety of property types -- from tree-filled neighborhoods to heavily-paved industrial areas -- through planting trees and vegetation, installing green roofs and using materials on roofs and pavement that reflect heat.

The modeling showed that the biggest differences came from using reflective materials and planting trees. Shandas said green roofs provided localized cooling of the roofs themselves, especially when watered, but that they needed to be studied further before they could be considered as a broader solution for urban heat. He noted, however, that green roofs provide other environmental benefits such as retaining storm water, controlling pollution and providing a habitat for wildlife.

New Study Shows Ways To Maximize Temperature Lowering Benefits Of Chicago’s Green Roofs
Jessica Sieff

Researchers have created an integrated framework to identify which neighborhoods would benefit most from green roofs -- and provide city officials with a strategic approach to ensure the best return on their investment to beat the heat.

Extreme heat poses a unique challenge to cities in the United States. According to the National Weather Service, extreme heat accounts for 20 percent of deaths by natural hazard in the United States, taking an average of 130 lives per year.

With exploding urban populations and increasing migration, cities are struggling to keep up with increases in extreme heat-related climate impacts, threatening human health, straining energy resources and reducing economic productivity. Heavily populated cities like Chicago have made an effort to mitigate the effects of extreme heat, implementing green roofs designed to provide insulation and significantly lower temperatures.

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