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The building sector has a significant impact on the natural environment. It consumes almost 33 of the worlds natural resources, including 40 of its energy and up to 12% of its water. These estimates do not consider embodied energy (i.e. the energy used to obtain, manufacture, use and dispose of building materials), which can represent a significant proportion of a building's lifetime energy consumption. The building sector is also responsible for 40% of global green-house gas (GHG) emissions and 40% of the waste which ends up in the landfills (World Green Building Council, 2006). The consumption of natural resources, particularly none-renewable energy sources, is an important factor in the economy of many nations. Authorative reports show such trends in many parts of the world. In the United Kingdom, for instance, the building sector consumes almost 50% of all the country's energy. While in the United States, about 40% of the total national energy production and almost 70% of electricity production is used in the building sector, as well as 28% in transportation - a factor which is partly influenced by urban design. The building sector in China currently accounts for 19% of the country's total energy consumption. This relatively small percentage is due to energy intensive industrial production. The same scenario occurs in the rich oil-producing areas of the Gulf Corporation Council Countries (GCCC). For example, the building sector in Kuwait account for nearly 45% of the yearly electric energy consumption, whilst in Saudi Arabia this sector consumes about 70% of the total electricity consumption. In Bahrain, the smallest country within the GCCC, buildings account for 83% of the national consumption of electricity (EIA, 2010).
Apart from its energy consumption, the building sector is also one of the largest contributors to changes in the environment and atmosphere: firstly, building construction, raw material processing and product manufacturing overall are the largest sources of GHGs. They account for some 40% of the world GHGs emissions. The building sector creates the most waste, habitat destruction and is responsible for the most pollution. Second, GHGs, particularly CO2, are the main by-product of fossil fuel energy consumption, and as buildings are, in total, among the largest consumers of energy, they are also the major contributor to the increase in CO2 emissions and hence global warming. While most available data related to these contributions are for the developed world, reports show that, on the whole, these contributions are worse in developing countries such as the GCCC. These countries have become major GHGs emitters. According to the International Panel of Climate Chang (2007), the GCCC are amongst the top countries in terms of CO2 emissions per capita. Recent statistics show an increase of CO2 emissions due to excessive energy consumption in different GCCC sectors, particularly the building sector. The increase in CO2 emissions had been within the range of 30-35% between 1997 and 2006. The GCCC are found to contribute two and half per cent of the global GHG emissions (United Nations Statistic Division, 2007).
One of the main principles of the GCCC is to enhance the economic and environmental actions related to the adoption of policies and unifying environmental laws as well as the conservation of natural resources (GCC, 2008). Within this context a two-fold policy aims at promoting energy regulations and sustainable developments has been adopted. A major role has been given to the building sector, with a special focus on the important role that efficiency regulations can play in reducing energy consumption and protecting the environment.
On the ground, some actions have been taken by the GCCC in order to achieve sustainability in buildings, such as the implementation of green building regulations. Most of these regulations are based on the USA's Green Building Council's (US GBC) Leadership in Energy and Environmental Design (LEED) rating system, with modifications made to account for the local environmental conditions. In terms of green construction, many attempts have been made in different parts of the GCCC. Examples can be seen in the Bahrain World Trade Centre in Manama, the large-scale Masdar City in Abu Dhabi, the campus of King Abdullah University of Science and Technology in Saudi Arabia and the Energy City in Qatar. These projects incorporate several efficiency techniques and green materials. A consideration of these huge, costly projects shows that three parties can benefit from such developments: governments and owners can save energy and protect the environment, thereby gaining a favourable image; contractors and suppliers can sell green products and developers can use the affirmative image as a positive marketing tool. However, in his article 'The Business of Green' Elsheshtawy (2010) claims that some green and LEED certified buildings in the GCCC end up consuming much more energy than the evaluators predicted due to poor energy practices. Coupled with this is the economics of energy efficiency and green buildings.
Cost of building green
A great number of available projects, such as those mentioned above, shows that if building green is a target at the outset of the design process and material selection then the cost of the green building is competitive. In a commercial setting, such projects can result in reduced energy consumption, saved environment, improved occupant health and comfort and reduced capital costs. Many rigorous assessments show that the overall cost of these projects is no more than that of any equivalent conventional project. Increases in first cost are reported within the range from five-ten per cent. During the construction phase the use of the green strategies, such as downsizing of costly mechanical, electrical and structural systems can increase the saving in initial costs, while during the first two decades the increases due to the use of green technologies will result in a savings of at least ten times the initial investment in operation costs for utilities such as electricity. In rental properties, owners are concerned only with the initial cost, especially in the cases where tenants are paying the bills. Governments and some owners, however, can realise the energy savings and so are willing to pay more for minimising the operation cost and reducing the environmental impact. The trade-off between economic costs and environmental benefits can stimulate people on the basis that adoption of green technologies will have environmental and social benefits outside the margin of cost consideration. Although the concept of eco-efficiency, in many cases, does not take into account the social benefits, such an approach can balance environmental design with cost-effectiveness.
To achieve eco-efficiency in the building sector, it is necessary to apply an integrated approach with the assistance of a team of professionals across different areas. This is realised in what is called the whole building approach. This approach represents a key factor in the design and construction of green buildings, especially with the advance of technology and increased complexity of constructional systems. The incorporation of the whole building approach at the project's conceptual design phase enables the evaluation of a building's design, materials and systems from the perspectives of all the project team members as well as from the perspectives of owners and occupants. A principal advantage of this approach is the coordination and mutual dialogue between project team members, which represent a cornerstone for any successful projects. By applying the whole building approach initial and other cost savings can be realised, energy efficiency evaluated and environmental impact assessed.
The role of cladding systems in making buildings green
Green buildings are generally designed and built in an ecological and resources-efficient manner. They often respond to their local environment and, therefore, different building designs are found in different regions. In any region, however, the ultimate target of green buildings is to provide a comfortable environment in an economic way. The building's skin, particularly building facade, represents the connection between the internal environment and the outside conditions, and hence a key function of the building facade is to reduce the need to modify the indoor environment as little as possible in response to the environmental load from the outdoor climate. Sometimes, a building facade fails to meet its objective due to one or more reasons, such as the insufficient design of wall systems or the inappropriate selection of cladding materials that probably make it impossible for any specific level of comfortable environment to be achieved. Then, it is necessary to rely upon electrical and mechanical systems to achieve comfort. This reliance leads to higher cost which is translated into bigger capacity requirements for lighting and mechanical equipment and higher capital costs for such equipment as well as larger amounts of energy consumption by the lighting system and heating, ventilation and air-conditioning (HVAC) system. In contrast, efficient environmental design and appropriate selection of green cladding materials can result in a comfortable inside environment, reduced project initial and running costs and a building that is energy and resource-efficient with lower operating costs than conventional buildings. Practitioners have demonstrated that the implementation of green strategies contributes to a building's comfort, economic and energy performance. The use of green cladding systems, in particular, is able to make a significant impact on the thermal and operational performance of green buildings. Reports show that when green cladding systems are taken into account at the conceptual design phase, significant improvements in the energy performance can be achieved (Radhi and Sharples, 2008).
Aside from their influence on building operational energy, the external wall systems and cladding materials are major contributors to changes in the natural environment. The production of construction materials such as precast and aluminium increases atmospheric concentrations of GHGs. The environmental impact starts with the chemical reactions during the production phase, where such materials represent one of the largest source of CO2 emissions and other GHGs. Then, the transportation of the materials to construction sites consumes considerable amounts of primary energy and generates high levels of GHG emissions. At the installation phase these materials generate different types of waste, whilst at the operation phase some of them influence the interior and exterior spaces by producing unhealthy components into the air. Some construction materials have relatively short useful lives and, consequently, the disposal and manufacture of replacement materials occurs, thereby generating more GHGs and waste. Research experts have shown that a careful selection of low environmental impact components and materials reduces the CO2 emissions by up to 30%. Some cladding materials are reported to have the capacity to reduce ozone emissions and other sources of pollutants such as CO2 (Radhi, 2010).
How can the eco-efficiency of cladding systems be measured?
The World Business Council for Sustainable Development (WBCSD, 2000) terms eco-efficiency as the synthesis of economic and environmental efficiency in parallel. Within this context, eco-efficiency in the building sector can be determined by three broad objectives:
Reduce natural resources consumption by minimising the use of embodied and operational energy, raw materials, water and land as well as enhancing recyclability and material durability
Reduce environmental impact by minimising GHGs emissions, waste disposal, water discharges and the dispersion of toxic substances, as well as encouraging the use of renewable resources.
Increase the value of materials and systems by providing more benefits through material functionality, flexibility and modularity.
In the light of these objectives the important question is how the eco-efficiency of cladding systems can be measured. Significant scientific work has been addressing this issue by introducing suitable assessment methodologies and rating systems. This is best seen in the environmental life cycle assessment (LCA) and life-cycle cost (LCC) approaches developed by the international standards for LCA principles and framework - ISO 14040 (ISO14040, 2006). Assessment is performed in four phases, including goal and scope definition, inventory analysis, impact assessment and interpretation. Two main approaches are available to classify and characterise environmental impacts. The first is the problem-oriented approach (mid-point). The second is the damage-oriented approach (end-point). A great number of methods have been developed under these two approaches such as the critical volumes (weighted load) and ecological scarcity (eco-points) systems in Switzerland, environmental priorities system in Sweden, eco-indicator 99 in Netherlands and the environmental problems system in the United States. The use of such methods makes it possible to select building systems and materials that achieve the most appropriate balance between environmental and economic performance based on certain values of the building team.
Case study: assessing eco-efficiency of cladding systems in Bahrain
The current assessment, based on the LCA of residential buildings (Radhi and Sharples, 2012), is performed to characterise the eco-efficiency of cladding systems in Bahrain. Bahrain is chosen as many of its building construction approaches and techniques are typical of those found in the GCCC. The production, construction, use and disposal of a 75 m2 front facade of a typical Bahraini house (Fig. 24.1), formed the basis of this assessment. Technically, the building facade consisted of two main components that included the wall system and cladding layers. The wall system is generally classified as cavity wall, barrier wall or mass wall (National Institute of Building Sciences, 2012). The cavity wall (sometimes called the screen wall system) is the preferred method of construction in many climatic regions due primarily to its ability to achieve pressure-equalisation. The barrier wall is an exterior wall system of assembly. The principal difference of this system is its ability to integrate the surfaces of outermost exterior wall and construction joints, which can offer resistance to bulk moisture ingress. The mass wall relies principally upon a combination of wall thickness and storage capacity. Some fundamental differences exist among these systems such as the thermal performance, fire safety, moisture protection, acoustics, maintainability and material durability, and so consequently their impact on the environment.
In terms of cladding, it is the exterior finish layer that is installed to cover wall systems and/or support structures. This finish layer serves several functions, including improving appearance, optimising thermal and environmental performance and keeping undesirable outdoor elements away. Today cladding systems are available in many forms and materials, which are often chosen based on economic and aesthetic factors. Structurally, the use of any alternatives of cladding determines the type of wall system and vice versa. The mass wall system, for example, can form structural elements or finished cladding systems. This system is commonly associated with plaster and masonry cladding systems. On the other hand, the barrier wall is used with precast concrete spandrel panels and some types of metal cladding systems such as composite and solid metal plate as well as with exterior insulation and finish systems (EIFS).
With the advance in building technology and construction materials, many alternatives of cladding systems are now available in the market. Examples are studied in the current work, namely, stucco, masonry veneer, marble, ceramic tile and the EIFS. Stucco is a hard, dense, thick and non-insulating material, such as cement plaster, that can be used to cover exterior wall surfaces. Both Portland cement and masonry cement are used with sand for the base and finish coats of stucco exterior walls. Unlike the ordinary stucco system, the EIFS (also known as synthetic stucco) is a lightweight synthetic wall cladding that includes foam plastic insulation and thin synthetic coatings. The masonry veneer is made from a mixture of Portland cement and aggregates under controlled conditions. It provides cladding and resists transferring wind and heat loads to the building support structure. The marble cladding system is a natural stone, while the ceramic tile cladding system consists of a mixture of clay and other ceramic materials. To improve environmental and thermal performance, recycled windshield glass is often added to the ceramic mix (Brookes and Meijs, 2008). These five cladding systems are assessed under real construction and thermal scenarios with the same wall system (mass wall), as illustrated in Fig. 24.2. To provide each scenario with the basic system's quantities per functional unit, the existing facade parameters and wall materials of the typical house are considered as a reference scenario, in addition to the operational aspects that are influenced by the building facade.
Data inventory of cladding systems
The LCA method and LCC technique are integrated to deliver a complete and detailed assessment of the overall potential impact of the typical house. An important point to note is that system and material selection based on a single impact could obscure other factors that might cause equal or greater damage. Therefore, the adopted LCA methodology takes a multidimensional life-cycle approach, in which multiple environmental impacts are considered over the entire life of the assessed cladding systems. To balance the assessment, the LCC is performed over a 60 year life span, and is based on published data and methods outlined in (Radhi 2010). Categories of expenditure typically include costs for purchase, installation, maintenance, repair and replacement. Measuring the economic performance is relatively straightforward by using real cost data collected through a field study. The data in question are the real cost data that occur and the subsequent cost, which will occur in the future.
Normalisation is carried out in this work in order to present a more useful scale of measurement and to make comparisons of various systems simpler. Normalisation is an optional step in impact assessment and can be described as a form of benchmarking, where the flows of each environmental impact are first summed and then divided by fixed Bahraini scale impact values. This can yield measures that are placed in the context of Bahraini activity contributing to that impact. The placing of each measure in the context of its associated Bahraini impact measure makes it possible to reduce different values to the same scale and allows the comparison across impacts. The resulting performance measures are, thus, expressed in non-commensurate units. For credibility, the commercially available BEES model (National Institute of Standards and Technology, 2007) for building construction materials coupled with the international inventory data (Hammond & Jones, 2011) were used to compare and check. The BEES model is generally used to measure the environmental and energy performance of building products and facade materials using the life cycle assessment approach outlined in ISO standard 14040.
Environmental impact assessment
Given the desire to link environmental and economic performance through the concept of eco-efficiency, the ideal way is to base the eco-efficiency indicators on international agreement as far as possible. According to the framework of the United Nations (2006), the assessment of eco-efficiency includes various generic environmental issues such as energy use, global warming contribution, water use, ozone depletion substance and waste. From these indicators, energy consumption and CO2 emissions, water use and ecological toxicity are of the greatest relevance for this study. Fig. 24.3 compares these indicators with respect to the five studied cladding systems. Some of these systems, such as the marble cladding, have significant impacts on water use but moderate impacts on global warming and embodied energy. Other systems, such as stucco, have a significant impact on both the energy consumption and global warming but a minor impact on water use. The others, such as the EIFS, have a minor impact on different generic environmental issues. From the illustration, the EIFS system seems to be the best performer, followed by the ceramic tiles, marble and finally the brick. Stucco is found to be the least effective system in terms of energy consumption and ecological toxicity as well as in relation to CO2 emissions. This can be related to the large amounts of CO2 emissions during cement production, which is the main component of the plaster cladding system.
Environmental versus economic
When the overall environmental impact of the examined systems is considered, a different scenario occurs. The overall environmental performance is illustrated in Fig. 24.4. Two main observations can be highlighted: firstly, the overall environmental performance ranking of the five systems is different from single measures such energy use and global warming. The EIFS cladding system is the best environmental performer, whilst the ceramic tile system is the worst performer. The difference is more than 24 points. As systems with lower scores are greener, the EIFS cladding system is greener because it contributes, on average, 0.1% of annual per capita Bahrain environmental impacts, whilst the marble contributes a larger share, 0.35%. Secondly, the environmental performance ranking is different from that of the economic performance. The illustration shows that the economic impacts of cladding systems are various and different from the environmental impacts. For example, the stucco cladding is illustrated as the best economic performer, but it is not in terms of the environmental performance. The difference in score is significant, being almost 11 points. This can be also seen in the case of the ceramic tile cladding. In contrast, the marble cladding achieves a high overall environmental performance and a low economic performance with a difference that reaches almost 21%. The EIFS cladding seems to have a balanced environmental and economic status. The same ranking occurs when both environmental and economic performance are estimated.
By using the multi-attribute decision analysis technique, environmental indicators and the economic performance are combined into an overall performance measure (National Institute of Standards and Technology, 2007). It is important to mention that the overall performance scores in this work are not indications of absolute performance. Rather, they are reflecting proportional differences in performance and representing relative performance among system alternatives. By following this procedure, these scores can be changed when the number of system alternatives are increased or reduced. The potential overall performance of the studied systems shows different scenarios when compared with the environmental and economic performances. The stucco cladding seems to be the most eco-efficient systems in spite of its poor environmental performance, followed by the EFIS system with a score of 29%, with the masonry veneer coming next. In contrast, the ceramic tile cladding is found to be the worst with almost 50%, in spite of its moderate economic performance.
Overall, different cladding systems have different environmental and economic performances. Some cladding materials improve the environmental performance, but provide a moderate influence in terms of economic performance, and vice versa. Others positively improve the environmental performance and can optimise the economic performance. Therefore, a careful eco-efficiency assessment should be undertaken in selecting wall cladding systems. Such an assessment can benefit the appraisal of green cladding systems and hence into the design decisions made in developing various scale of green buildings.
Today's modern buildings systems, particularly cladding system, are often selected and assessed based on aesthetics and cost rather than their environmental performance or their overall potential impact. The concept of eco-efficiency introduced in this book balances the environmental performance with economic aspects. This chapter presented a systematic eco-efficiency assessment of cladding systems and explored its role progressing a green future in the building sector. The interrelation between environmental indicators and economic performance was examined by comparing various cladding systems, considering both overall environmental impact indicators and life cycle cost. The differences in environmental indicators of various cladding systems, namely, stucco, masonry veneer, marble, ceramic tile and the EIFS systems, are generally significant. The ranking of these systems in terms of environmental and economic performance are different. Some of the cladding systems, such as the marble cladding, reduce energy consumption and CO2 emissions, but provide a minor reduction in terms of the life cycle cost, and vice versa. Others, such as the EFIS system, impact positively upon the environmental indicators and can optimise the overall potential impact. This system has the ability to reduce energy consumption and CO2 emissions; however, other aspects, such as maintenance and life expectancy, should be considered at the time of system selection.
The scope of the current study focused on the eco-efficiency of representative residential cladding system in a developing country. Consequently, the outcome of this assessment may not be applied to buildings in countries with different economic and environmental situation. In spite of this shortcoming, this assessment approach may provide useful quantitative and qualitative information for cladding design decisions. Therefore, it is important to highlight some general notes:
New green building technologies, such as the exterior insulation and finish systems (EIFS), are effective cladding systems in promoting a green future in the residential building sector.
To improve the overall potential impact, wall cladding systems in desert climate regions, such as Bahrain, can be designed as exterior insulation and finish systems.
Every building is unique in both design and operation. Academic experts and practitioners benefiting from this work should consider the impact of related variables, and therefore a careful assessment must be performed during the selection process in order to achieve eco-efficiency in the building sector.
In addition to its ability to assess building cladding systems, the eco-efficiency concept can be used with various other systems, materials and innovative applications. It can yield a precise assessment in the case of multifunctional problems in relatively short times and at relatively low cost. In the near future the concept of eco-efficiency will become more important in the context of the green built environment in order to show which design process, building systems and renewable technologies are more favourable than other alternatives.