Development of a modular system for vegetated surfaces in new buildings and retrofitting 1
Maria Manso , Ana Virtudes , J.P. Castro-Gomes
C-MADE, Centre of Materials and Building Technologies, Department of Civil Engineering and Architecture, University of Beira Interior, Covilh達, Portugal 1
firstname.lastname@example.org, email@example.com, firstname.lastname@example.org
Abstract The effectiveness to implement green surfaces in buildings depends mostly of the interest and awareness of citizens and investors of their advantages. However, its implementation also depends on the simplification of the construction process and the adaptation to new and existing buildings. An analysis of the main green roofs systems available in the market based on the study of their composition, materials used and construction methods, shows that there are some difficulties in its general use. This work presents an interdisciplinary ongoing study for the development of a design concept either for green roofs or facades. It consists of a modular system based on pre-fabricated panels incorporating vegetation. The panels are constituted of layers of different materials, combining low density, porosity, water retention, thermal isolation, strength, durability and fire resistance. The concept being developed can be used to create vegetated surfaces on new or retrofitted buildings. Non-conventional alkali activated binder materials are used to build the panels of the system. The modular system can be self-supporting. It holds the growing media for plant development and can retain irrigation water for its use. This modular system can be adapted to different shape surfaces, sizes, inclinations or inaccessible places of buildings, which is designed to simplify the implementation and maintenance processes. Therefore, it can be used in densely parts of cities, where conventional green spaces are not feasible, bringing nature to the urban context.
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Authors’ Biographies Maria Manso is an Architect and PhD student of Civil Engineering at University of Beira Interior, developing the thesis "Modular system design for garden surfaces with alkali-activated materials". Currently is part of the research team of the R&D project: GEOGREEN “Waste geopolymeric binder-based natural vegetated panels for energy-efficient building green roofs and facades”, financed by FCT, Portugal, in course at C-MADE, Centre of Materials and Building Technologies (www.c-made.ubi.pt).
Ana Lídia Virtudes is a Full Professor at Civil Engineering and Architecture Department of University of Beira Interior (UBI), with research interest in urban design and town planning. Researcher of C-MADE, Centre of Materials and Building Technologies and part of the research team of the R&D project: GEOGREEN “Waste geopolymeric binder-based natural vegetated panels for energy-efficient building green roofs and facades”, financed by FCT, Portugal.
João Castro Gomes is a Full Professor at Civil Engineering and Architecture Department of University of Beira Interior (UBI). Scientific Coordinator of CMADE, Centre of Materials and Building Technologies (www.c-made.ubi.pt). His research interests are durability of building materials; sustainable new binder-based composites; and technologies for sustainable construction. Currently is coordinating the R&D project: GEOGREEN “Waste geopolymeric binder-based natural vegetated panels for energy-efficient building green roofs and facades”, financed by FCT, Portugal.
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Background Industrial Context The system presented is still in development. It is in the design phase and prototyping. Thus, there is no related industrial context background information to provide. The study is supported by FCT – Foundation for Science and Technology - Portugal, within the research project GEOGREEN “Waste geopolymeric binder-based natural vegetated panels for energyefficient building green roofs and facades”.
Problem The paper presents and discusses the design development of a modular system for either green roofs or facades. It consists of a modular system based on pre-fabricated panels incorporating vegetation. The concept being developed can be adapted to different shape surfaces, is designed to simplify the implementation and maintenance processes and can be used to create vegetated surfaces on new or retrofitted buildings.
Learning Objectives: •
Finding new strategies to improve urban environmental conditions.
Analyse green roof benefits to the urban environment and building envelope.
Study the main characteristics of roof systems in terms of their composition, materials and construction methods.
Present the development of a design concept for green roofs or facades that can be used to create vegetated surfaces on new or retrofitted buildings.
Describe an interdisciplinary on-going study for the development of a modular system based on pre-fabricated panels incorporating vegetation.
Approach The paper presents and discusses the on-going design development of a modular system for either green roofs or facades. It consists of a modular system based on pre-fabricated panels incorporating vegetation. The concept being developed can be adapted to different shape surfaces, is designed to simplify the implementation and maintenance processes and can be used to create vegetated surfaces on new or retrofitted buildings. A literature review based on the analysis of different green roof and green wall systems, either available on the market or patented systems allowed the understanding of the main features, construction techniques and materials applied in these systems. This analysis was fundamental to the definition and design of a versatile modular building system, suitable for the construction of green roofs and green walls. World Green Roof Congress, 19-20 September 2012, Copenhagen Page 3
Non-conventional waste-based materials (alkali activated binder materials) for panel structure are being used. Various compositions of these materials are being experimented combining low density, porosity, mechanical strength, durability and fire resistance.
Analysis Introduction: Green roof urban initiatives Environmental conditions of urban areas are becoming deteriorated, due to crescent pollution, densification and lack of green areas (Virtudes et al., 2012b). The replacement of green areas for impervious surfaces, which retain more solar radiation then vegetation leads to increasing urban temperatures and difficulties of rainwater drainage. Vegetation has several benefits to the urban environment (Virtudes et al., 2012a). It has the ability to absorb CO2 and retain dust particles, contributing to improve air quality, mitigate the urban heat island effect and improve biodiversity in the urban context. The insertion of vegetation in urban areas influences visually and aesthetically the surroundings, besides the fact that it is recognized for its therapeutic benefits. In fact, large green areas are known to have a significant influence the surrounding conditions, air temperature and humidity, creating a specific microclimate. Green roofs are an interesting strategy of greening in dense urban areas with lack of free space (Virtudes et al., 2011), allowing the integration of vegetation without soil occupancy. The effectiveness to implement green surfaces in buildings depends mostly of the interest and awareness of citizens and investors of their advantages. Green roofs can also contribute to the improvement of urban environment and have a significant influence on stormwater management. They are able to retain rain water and use it for plants development. As recognition of green roof advantages in the urban context, recently have emerged new urban initiatives all over the world to incentive the implementation of green roofs. These incentive programs tend to emphasize the advantages and benefits of greening the urban environment. In Chicago green roofs are a central aspect in its sustainable development policy. The city has already around 600 green roof projects which represent 651.000 square meters of covered roofs. This initiative started in 2000, by Mayor Richard Daley with the coverage of Chicago City Hall (Snodgrass et al., 2010). Local authorities give financial support and prepared a guide for the implementation rooftop gardens. This guide indicates the main requirements for the installation of accessible roof gardens, mentioning the roof barriers, structural weight capacity and security conditions (Chicago Green Roofs, s.d.). Other American cities like Portland and Philadelphia have similar programs to encourage the use of green roofs implementing stormwater management strategies (Snodgrass et al., 2010). The Toronto City Council adopted in 2009 an Eco-roof Incentive Program, which focus on the implementation of green roofs, besides other passive solutions, in business buildings (Toronto Green Roofs, s.d.). World Green Roof Congress, 19-20 September 2012, Copenhagen Page 4
In order to become a carbon neutral city by 2025, Copenhagen has a goal to achieve 150,000 square meters of green roofs by 2015, in new and existing buildings, providing also some guidelines for its implementation (City of Copenhagen, 2012). In the revision of the Municipal Director Plan of Lisbon are already integrated some environmental concerns, centred in the reduction of the city´s energetic needs and “green house” gases. The integration of green roofs is mentioned as a complementary solution to improve the environmental quality of dense urban areas. Green roofs can contribute to improve the city´s image, while mitigating the heat island effect and delaying the launch of rainwater to the drainage system (AA.VV., 2011). Local initiatives can make the investment in green roof construction more attractive for investors. It is why is important to inform owners about green roofs benefits, correct implementation and maintenance. Analyzing the experience of pioneering cities can be a good way to achieve better results in incentive programs of other cities. However green roofs influence in urban environment depends on the city scale, and on the size and vegetation structure of green spaces (Oliveira et al., 2011).
Impact of green roof systems in buildings envelope Roofs are intensively exposed to wind, direct solar radiation and extreme temperature fluctuations, which can affect the roof membranes longevity and buildings thermal loads. Buildings with dark hard exterior surfaces, in temperate regions, have lower albedo (reflectivity) than vegetated surfaces (Weiler et al., 2009) (Lundholm, 2006). The inclusion of vegetation and soil in roofs mitigate this effect by reducing the solar radiation absorption (Eumorfopoulou et al., 1998), which leads to a temperature reduction of building’s exterior surfaces (Wong et al., 2003) (Liu et al., 2003) and lower heat transfer into interior spaces. Vegetation is able to shade the surrounding surfaces of buildings while it absorbs sunlight to develop its vital functions (photosynthesis, respiration, transpiration and evaporation). In Mediterranean climates the shadowing effect of vegetation installed in the roof can have a significant impact on the solar radiation transmitted into building’s interior during summer (Barrio, 1998). With the integration of green roofs in existing flat roofs, the diurnal temperature range experienced by roof membrane is reduced significantly (Connelly e Liu 2005). They protect the waterproofing materials and avoid the degradation caused by the action of direct solar radiation (Kosareo et al., 2007) (Saiz et al., 2006) (Luckett, 2009). Green roofs can be used as a passive design strategy, contributing to buildings thermal performance, by protecting the roof against extreme temperatures (Eumorfopoulou et al., 1998). When compared to other roof assemblies it can be noticed a significant decrease of the median daily temperature fluctuation in roof membrane (Liu et al., 2003). Simultaneously green roofs contribute to the decreasing of heat flow through the roof, which can reduce significantly the daily average demand for cooling interior spaces (Liu et al., 2003). World Green Roof Congress, 19-20 September 2012, Copenhagen Page 5
Some thermal studies indicate that most energy consumption during using phase in buildings is related to HVAC systems (Kosareo e Ries 2007). Several studies indicate that green roofs contribute to the reduction of power consumption of cooling systems (Kosareo et al., 2007) (Wong et al., 2003) (Connelly et al., 2005) (Liu et al., 2005). Green roofs substrate layer complements the roof thermal insulation and increase its thermal inertia (Campredon et al., 2002). However, substrate layer insulation properties depend on its composition and moisture content. To improve green roofs insulation properties it is preferable to select lightweight soils with high capacity of moisture retention (Barrio, 1998). The intensity of wind also has a great influence on heating demands of buildings (Peck et al., 1999). Wind has the capability of cooling the building envelope. It is why protecting the building envelope with plants can have influence on the insulation effectiveness of the building.
Construction process of green roofs There are several green roof systems on the market. The decision of which is more appropriate to a certain project depends on the building characteristics, its localization and local climate. In order to identify and systematize the main green roof systems available in the market it is important to study their composition, materials used and construction methods. Usually are identified three main green roof systems: extensive green roofs, semi-intensive green roof and intensive green roofs systems. They all differ in type of vegetation, substrate thickness and composition of drainage layers. Extensive green roofs are lighter than others. They including a thin layer of substrate, which limits the type of plants included (e.g. sedum, mosses, herbaceous or grasses). These are easily applied, without major technical difficulties. They can be a good solution to improve the conditions of non accessible roofs and existing roofs, without overloading the building structure (Peck et al., 1999). These can be applied in flat or pitched roofs until 30o, covering extensive areas with short maintenance and irrigation, which reduces its usage cost. Intensive green roofs are more suitable for accessible green roofs, with capacity for higher loads. They include a thicker layer of substrate (from 150 mm to 400 mm or over 1000 mm) which allows the integration of grass, shrubs and small trees. They can also contribute to thermal and acoustic insulation by containing a thicker substrate layer than extensive solutions. However, these systems require regular maintenance and irrigation (Peck et al., 1999). Some authors report the existence of a third classification, semi-intensive green roofs (Dunnett et al., 2010). These systems have intermediate characteristics, seeking to incorporate features of extensive and intensive systems (Newton et al., 2007). These systems contain an intermediate thickness, allowing the integration of a large number of plant species than extensive solutions minimizing the need for maintenance and watering.
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Figure 1 – Green roof in the Cultural Centre of Belém, Lisbon, Portugal (Petrone 2009).
Figure 2 – Gulbenkian green roof, Lisbon, Portugal (Argonautes 2010).
Green roofs have evolved into simpler solutions, allowing the creation of vegetation covers in a shorter period of time. In this context have emerged the modular and continuous pre-planted solutions. Lighter and modular solutions allow the replacement of segments of green coverage, making maintenance and repair more resourceful. Some solutions, either modular or continuous, enable not only the installation in flat roofs, but also in pitched roofs. To avoid the substrate sliding it can be applied a retaining layer, which can also promote plant rooting to avoid loss of substrate by erosion. Continuous green roof systems integrate a set of layers in order to protect the roof structure and improve the system performance. Each layer responds to different needs, such as: waterproofing layer, root barrier, drainage layer, fine particles filtering, growing medium and vegetation. These elements may be inserted in roofs with a minimum slope of 1.5 to 3%, to provide an adequate drainage. Besides these layers, green roofs can integrate thermal or acoustic insulations. Most common continuous systems contain a thermal insulation layer under the waterproofing layer. However, there are also inverted systems which contain insulation over the waterproofing layer (Lopes, 2005).
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The main difficulties to implement green roof systems are centred in their construction and maintenance. The building characteristics must be analysed before installing a green roof system, either if it is still in construction or is being rehabilitated. Therefore, it is important to verify the structural capacity of the roof, if it will be accessible or non accessible, the parapet height available for roofing layers and the roof slope. The main difficulties in most green roof systems are the reparation and replacement of the waterproofing membrane, the retention of humidity for plant growth, avoiding the migration of fine particles and the replacement of unsuccessful vegetation. An analysis of the most recent green roofs solutions allowed the identification and systematization of the main features of green roof systems, according to their composition and applicability. It appears that innovation arises through the design of light and extensive solutions. These can be grouped into two main categories, continuous systems and modular systems. To simplify the application and lightning the structure of continuous systems is commonly referred the use of polymeric materials. These materials can be manually transported in coils to the roof and applied through the overlap of different layers. In these systems is also common to use pre-grown vegetation carpets, which give a finished image to the green roof. Modular systems have advantages in installation and maintenance, revealing a relatively new area of marketing. They enable the removal of each module individually for maintenance purposes. Most modular systems consist of a modular container filled with growth medium for plants. Containers are mostly produced in light molded materials, such as plastic or steel, with reinforced sides and bottom to support the load of growing medium. Most extensive systems use low density growing mediums combining organic and inorganic materials. To avoid substrate loss due to the lightness of the system, the modules can integrate non-woven materials that promote plant root and anchor. The main concern of modular systems is to simplify the construction and maintenance processes. Modular containers have mostly a quadrangular configuration, with size and weight to allow handling for maintenance purposes. They may be produced in one piece or consists on the assembly of several elements with different characteristics to complete each module. Some solutions also integrate side grooves to ensure the continuity of the system. To allow a better green roof performance, all systems integrate means of drainage, irrigation and rainwater recovery. Most containers have a textured background with water deposits and channels to reduce the need for irrigation. This allows storage of excess rain or irrigation water and its distribution through the entire surface. The surface of the roof must be properly sealed and should contain roots and vapor barriers to avoid its deterioration. Although most solutions donÂ´t focus the conditions of the supporting structure, its protection is fundamental for the roof longevity. The lightness and assembly simplicity of extensive modular or continuous systems makes them suitable for buildings rehabilitation. World Green Roof Congress, 19-20 September 2012, Copenhagen Page 8
On-going study Design concept of a modular system for vegetated surfaces The knowledge obtained from the study of different features, construction techniques and materials of several green roof systems was fundamental to the definition and design of a new modular building system. It appears that most solutions focus on solving one constructive solution. In fact most solutions are not able to function as green roofs and green walls simultaneously. The goal is to develop a versatile solution, for green roofs and green walls, considering the particularities of each surface. Therefore it must be taken into account the materials selected and the operational requirements of the system when applied on surfaces with different inclinations.
Figure 3 â€“ Public Farm, New York City, USA (Adams 2008)
In the context of a research project is being developed a new design concept for a prefabricated modular system where can be inserted pre-planted vegetation to create green horizontal, vertical, inclined or curved surfaces. The modular system in development can be used to create green surfaces on new or existing buildings or can be self-supporting to create isolated green surfaces, independent from any building surface. The simplification of the construction process allows the adaptation of this modular system to surfaces with different shapes, sizes, inclinations or accessibilities. The main goals of the modular system design are: simplification of the construction process; ease of maintenance; vegetal layer uniformity and continuity; minimization of plant irrigation; and improvement of buildings envelope thermal, acoustic and environmental properties.
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An unique and functional system, easy to assemble and disassemble is intended as result. The modular building system is designed to allow easily installation of green surfaces by allowing replacement and maintenance of each module individually when in normal functioning.
Figure 4 â€“ Modular system for vegetated surfaces side view
The design concept privileges the reuse of industrial waste materials. Each module comprises a geopolymer base plate comprising mine wasting sludge and an upper plate comprising cork waste. The base plate is made of a porous and permeable binder-based geopolymer with mechanical and chemical resistance, durability, fire resistance and water retention capacity. This material absorbs the water and slowly releases it to the substrate, minimizing the irrigation needs. The upper plate is made of expanded cork waste which has low density, high thermal isolation, fire resistance and sufficient mechanical strength to support the saturated substrate and the vegetation.
Use of alkali activated binder materials for panel production Another aim of this study is to integrate alkaline activated materials in the system, obtained from mining and quarrying wastes. This option tends toward sustainability concerns, such as the minimizing the embodied energy and CO2 emissions of the system itself. The development of alkaline activated binders (geopolymers) using alumina- silica based waste mud from mining and quarrying industry are considered to be most promising, both from an environmental and economic point of view (Torgal et al., 2008), (Torgal et al., 2009), (Zhang et al. 2011). Geopolymerisation is a highly complex process, and most common raw material classes used in geopolymerization are metakaolinite, industrial wastes like slags and coal fly ashes (Duxson et al., 2007). Other waste materials sources, like mining waste mud can also be successfully used to produce geopolymeric/alkaline activated binders (Torgal et al., 2008). The microstructure and mechanical properties are known to depend strongly on the chemical compositions of the starting materials (Duxson et al., 2005), (Okada et al., 2009), (Duxson et al., 2006). Durability properties of geopolymers are excellent, particularly resistance to acidic attack, behaviour at high temperatures and fire resistance, and as well resistant to frost attack (Rangan, 2009). World Green Roof Congress, 19-20 September 2012, Copenhagen Page 10
Therefore, from the technical point of view, geopolymers are presented as an alternative solution for concrete production, however the cost of these geopolymers can be up to twice as high as Ordinary Portland Cement (OPC) concrete (McLellana et al., 2011). Thus, it is desirable, from the start, to develop added value produtcs, which can make economically viable transforming industrial waste materials (like tungsten mining waste mud) into geopolymeric binders. Aditionally, some studies have quantified the environmental impact of geopolymers production using fly ash, blast furnace slag and metakaolin as precursors (Habert et al., 2011). The study shows that production of different types of geopolymer concrete had a slightly lower impact on global warming than standard OPC concrete. Geopolymer made from fly ashes or granulated blast furnace slags requires less sodium silicate solution for activation and, therefore, has a lower environmental impact than geopolymer made from pure metakaolin. In order to reduce carbon emissions, geopolymer production should use waste-based precursors with low sodium silicate solution. Therefore, manipulating the technology of geopolymer production it might be possible reduce some process energy, making the geopolymer greenhouse emissions several times lower than the values obtained with cement production. Thus, considering the technical, environmental and economical issues, alkali activated binder materials for panel structures are being used. Various compositions of these materials are being experimented combining low density, porosity, mechanical strength, durability and fire resistance. Alkaline binders are being produced using waste mud from Panasqueira mine located in Portugal - one of the most important and largest tungsten mines in the world. Such waste mud presents very good reactivity with alkaline activators after a thermal calcination process and under certain mixing conditions. Preliminary results showed that these mining waste binders presented good durability performance regarding abrasion and acid resistance, as well as environmental performance in leaching tests (Torgal et al., 2010).
Acknowledgments This work results from an ongoing research project â€œGEOGREEN - Waste geopolymeric binderbased natural vegetated panels for energy-efficient building green roofs and facadesâ€? integrating an interdisciplinary research team. The team is studying the development of a modular system based on pre-fabricated panel incorporating vegetation to build green roofs and green walls. The research is carried out in C-MADE, the Centre of Materials and Building Technologies of the Department of Civil Engineering and Architecture of University of Beira Interior, in CovilhĂŁ, in a partnership the School of Agriculture of the Polytechnic Institute of Castelo Branco.
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Results and Business Impacts Key Findings Several cities all over the world are concerned in implementing new strategies to improve their urban environmental conditions. These initiatives have different approaches to encourage the application of green roofs in new and existing buildings. Green roofs have shown to be beneficial to the urban environment and buildings envelope. However, green roof and green wall solutions are still limited in their applications. An on-going research is developing a new and flexible design concept for a prefabricated modular system to create horizontal, vertical or inclined vegetated surfaces. This modular system is designed to be used in new or retrofitted buildings. The system aims to include industrial waste materials which characteristics improve the system efficiency and buildings performance.
Business Impacts The design concept of a modular system based on pre-fabricated panels incorporating vegetation emerges from the intention to create a system which: simplifies the construction and maintenance processes, minimizes plant irrigation and improves buildings performance. The intention is to design a flexible modular system for horizontal, vertical or inclined vegetated surfaces for new or retrofitted buildings. The system differs from others by integrating sustainability concerns through the reuse of industrial waste materials, which characteristics contribute to the system efficiency and to buildings envelope performance.
Conclusions It is important to find new solutions to improve urban environmental conditions. In this context, many urban initiatives, with different approaches, are emerging in several cities to incentive the implementation of green roofs. Green roofs have several associated benefits for the urban environment and buildings envelope. In fact, green roof solutions allow the insertion of vegetation in urban areas without any soil occupancy, which is why they are becoming a potential strategy for greening in dense urban areas. Most green roof and green wall systems are not able to solve more than one constructive solution. So, there is still the possibility to develop new solutions which allows the construction of horizontal, vertical or inclined vegetated surfaces. The intention of the on-going research is to develop a flexible design concept for a prefabricated modular system for vegetated surfaces, which can be used in new buildings or be integrated in the rehabilitation of existing buildings. The modular system is being designed to simplify the construction process and maintenance, allowing the removal of each element individually. This system differs from the others by integrating sustainability concerns through the reuse of industrial waste materials in the geopolymer and cork compositions. The characteristics of these materials contribute to the efficiency of the system and to the performance of buildings envelope. World Green Roof Congress, 19-20 September 2012, Copenhagen Page 12
Key Lessons Learned: •
It is important to find new strategies to improve urban environmental conditions.
Green roofs can be an interesting strategy to solve some urban problems.
Most green roof and green wall systems are designed to respond to only one constructive solution.
It is still possible to design a new and flexible solution for green roofs and green facades that can be used to create vegetated surfaces on new or retrofitted buildings.
New materials are being used in an interdisciplinary on-going study for the development of a modular system based on pre-fabricated panels incorporating vegetation.
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