SUSTAINABLE CONSTRUCTION

a. What are the major environmental areas of deterioration?

b. Discuss briefly the principles of Sustainable Construction articulated by the CIB [the
Conseil International du Batiment] in 1994.




Environmental Areas of Deterioration

Since the last century, especially after the Second World War, the world population started to increase manifolds from about 2.3 billion in 1945 to about 6.9 billion in 2009. Parallel with the increase in population is also the increase in human activities that carry with them greater use of material, technology and energy for development. Such unstoppable development that utilizes environmental resources in the quest for a better quality of life has led to environmental quality deterioration.

In the past, if we were to consider human existence on this planet, the nature of human security was mostly related to natural disasters such as earthquake, landslide, and volcanic eruption, forest fires due to lightning, storms, and rise in sea level, flood, drought, and attacks by hostile enemies and wild animals. A number of the past natural disasters had inflicted not only sufferings but also destruction of human beings and their habitats.

The increasing incidences of below area had affected global environment as well as human security:
- Atmospheric Pollution - Reduction in emissions of sulphur dioxide and suspended particulates, lead and CFCs, but sharp increase in emissions of GHG such as CO2, methane, ozone and nitric oxide (industrialization, transport);
- Aquatic Pollution - Improvement with regard to point sources of inland water pollution, but increased pollution from non-point sources (notably agriculture), threat to water quality, eutrophication of fresh waters and pollution of marine waters;
- Soil Degradation - Inadequate waste management, risks arising from industrial activities, increased spreading of nitrates and sewage sludge in agriculture, increased use of hyper-intensive farming, excessive use of chemical fertilizers, pesticides and herbicides, acidification and desertification in some areas;
- Nature Conservation - Threats to biota and their natural habitats, reduction in biological diversity, deterioration of the coastal environment, mountain and forest areas (fire);
- The Urban Environment - Deterioration of the living environment due to pollution, noise, and damage to the architectural heritage and public places;
- Waste management – Increased amounts of domestic and industrial waste, poor use of recycling and reuse options.

Deteriorating quality of the environment slowly, but steadily poses a threat to human security. To counter the threat caused by environmental quality deterioration that interrupt the human security, many countries in the world already have environmental management system through legislative and non-legislative measures. However, the various efforts undertaken by the relevant government agencies do not seem to be successful in stopping further environmental quality deterioration as the actions taken are not really coordinated and integrated especially when it comes to implementation of laws and regulations, and thus the threat to human security is not really checked.

The environment is a big natural process system that consists of various subsystems as atmosphere, hydrosphere, lithosphere and biosphere that are uniquely interactive in nature. The various subsystems are closely inter-linked through their own natural processes and the myriad of interactions ensures an equilibrium condition is achieved through space and time. Interactions between the various subsystems are of vital importance to human beings.

In fact, each individual component of the physical environment has the ability to fulfill a variety of human requirements. The atmosphere supplies the most vital gas in the form of oxygen directly to human beings for respiration and there are also other gases in the atmosphere such as CO2 and nitrogen that are important to human life, indirectly. The atmosphere is also used for aviation.

Lithosphere, which forms the surface of the earth is not only important as a platform where societies can build settlements and carry out their activities, but also forms a base for the growth and livelihood of various species of flora and fauna. It is also used as a base for agriculture and various other human activities and embedded in it, either on land or under water, are many natural resources such as minerals that can fulfill human needs. The hydrosphere supplies water to support life and are used in various other forms such as for the purpose of navigation, to support agriculture, recreation and as a source of numerous varieties of aquatic foods. The biosphere, where human being is part of it, supplies societies with food and other resources in the form of flora and fauna. Therefore, it is very clear that the various physical components rely on each other to form a natural process system and in turn they are linked to the human use system.

Over the past several decades, scientists’ understanding of the complexities of the earth system has evolved to a point where they now recognize that the components of the system are inextricably intertwined. A change in one part of the earth’s system has repercussion for other parts – often in ways that are neither obvious nor immediately apparent. Indeed, the physical environment is very sensitive to disturbance either natural or due to human activities. Natural disturbances always exist. However, in most cases the natural disturbances always act towards achieving a dynamic equilibrium state. In fact, dynamic equilibrium can be achieved naturally, but the time frame of the whole process depends on the magnitude of the disturbance. In the case of disturbance as a result of human activities, the physical environment will still have the ability to upset it as long as the disturbance does not exceed its optimum ability to achieve equilibrium. Once the optimum level is exceeded, the physical environment starts to deteriorate.

It should also be realized that the damage that society causes to the environment is a product of three factors: the total number of people, how much each person consumes to maintain his or her standard of living, and how much environmental damage incurred in producing the goods consumed. Apparently our ability to change the global environment increases along with our numbers, our quest for and achievement of affluence, and our technological and institutional capabilities. Increasing number of people means more manufactured goods and services required to provide for their needs, which in turn means more waste material to be discharged into the environment.

The concentration of people in urban areas compounds the problems. Eventually the dilutive capacity of the air, water, and land in major urban-industrial areas becomes greatly exceeded and a serious pollution problem results. As real income increases, people are able to buy and consume more goods and services, throw them away more quickly to buy something better, travel more miles per year using various forms of transportation, and expand their usage of energy.

In the process much more waste material is generated for the society as a whole. Changes in technology have expanded the variety of products available for consumption, increased their quantity through increases in productivity, made products and packaging more complex, and raise the rate of obsolescence through rapid innovation. All of this has added to the waste disposal problem. In addition, the toxicity of many materials was originally unknown or not given much concern, with the result that procedure for the abatement of these pollution problems has lagged far behind the technology of manufacture.

These intertwining factors, the product of decisions made by individuals and societies around the world, are the main forces driving change in the global environment. It may be argued that no matter what society does, it is unlikely that we could suppress the powerful physical and chemical forces that drive the earth system. Although society cannot completely disrupt the earth system, we do affect it significantly as we use energy and emit pollution in our quest to provide food, shelter, and a host of other products for the world’s growing population.
The changes facing the planet today are distinguished from previous changes by the scale and pace with which they are occurring or are likely to occur. Over the geologic past, conditions in the atmosphere, ocean, and biosphere have for the most part followed natural cycles. Now, human activities are a significant force driving changes that lead to environmental quality deterioration, which is a manifestation of the interaction between natural process system and human-use system.

Environmental Quality Deterioration
Studies on many parts of the world suggest that as we extended our natural abilities with tools and later learned to cultivate plants, we became an effective agent of environmental change. Such changes become more apparent in terms of space and time as society progresses further. However, in the quest for development and economic gains, more often than not, society tends to forget about the environment that supplies the much-needed resources. As such, the mismanagement or the lack of planning and management has resulted in environmental quality deterioration and pose a threat to human security.

The presence of a long history of pollution control in some countries, especially developed countries, implies that these countries have a long history of environmental quality deterioration. The problem related to climate change that affects the world population was related to human activities, especially since the industrial revolution. It was mentioned that CO2 concentration in the atmosphere increased due to burning of fossil fuels.

However, the recent furore over the changes society has wrought in the global environment since industrialization began invites the assumption that human alteration of the earth’s landscape is a fairly recent phenomenon. In fact, many of society’s effects on the environment did not reach their global scale until the latter half of the twentieth century. Two of the most serious environmental problems are global warming due to greenhouse gases and ozone depletion. These problems are global because they affect everyone and every country in the world to some degree.

In fact, CO2 concentrations are currently increasing each year. Increase in CO2 concentrations and other green house gases in the atmosphere will lead to increase in global temperature which has greater consequences in the form of melting of ice sheets and permanent permafrost, rise in sea level, atmospheric disturbances that lead to flooding, drought and forest fires. Such consequences of environmental quality deterioration will certainly threaten human security.

Environmental Quality Deterioration and Human Security
There are both biophysical and social vulnerabilities associated with development and these vulnerabilities affect human security. The biophysical vulnerabilities include the fragile environments of a nation, limited land resources, shortage of basic resources, and the risks associated with climate change. The ability to respond to these problems is constrained by social vulnerabilities, notably weak economies, difficulties associated with land ownership, and institutional limitations. The objective of human security is to safeguard the vital core of all human lives from critical pervasive threats, without impending long-term human fulfillment.

However, the relevant elements of human security will differ radically depending on the expertise, size and capacity of the implementing institution, as well as the activities that are being effectively undertaken by other institutions in the context. Furthermore, identifying the elements of human security is as much a value judgement as it is an explorative exercise. As such to identify the elements of human security is useful only in conjunction with other questions regarding the institutional environment and the views of the people.

As mentioned earlier, the physical environment supplies human beings with vital natural resources such as air, water, land and food. Life is secured with available supply of these resources, but if supply is somehow disrupted or unavailable the situation will lead to human insecurity. History has shown that human beings are willing to go to war to secure their hands on these vital resources – water, food and of late, even petroleum. Climate change triggered by human infliction on the quality of the environment in the last few decades has caused much sufferings and threatened human security.

The presence of air pollution in the form of suspended particulate matter, carbon monoxide, hydrocarbon, sulphur oxides, nitrogen oxides and ozone in the urban areas has been mentioned to affect human health and well-beings especially in urban areas. The frequent occurrence of haze due to cross-boundary and local sources has also threatened human security. During the last few decades human security was threatened on a number of occasions due to pollution by diesel, ammonia and effluents from industries in the domestic water supply. Apart from these, there are also problems related to the improper disposal of clinical waste and toxic and hazardous waste to the environment.

Deforestation, agriculture and infrastructure development has also caused further environmental quality deterioration that is illustrated by more frequent occurrences of flash flood especially in urban areas, and higher frequency and geographical extent of seasonal flood which all affect human security. The environmental quality would not have deteriorated to such an extent until it becomes a threat to human security if there exists an effective environmental management system.

Environmental Management
All active persons practice some degree of environmental management but the term is interpreted here as a conscious, systematic effort by one or more individuals acting in concert to produce an aesthetically pleasing, economically viable, and physically healthy environment. Environmental management is the influencing of human activities as they affect the quality of mankind’s physical environment, especially the air, water, and terrestrial features.

The introduction of energy, material and technology in the interaction between human use system and physical environment system will not only lead to development success but also environmental quality deterioration where both would require a form of environmental quality management system. Environmental management is carried out through a number of measures either legislative or non-legislative.


The legislative measures that are in the form of licensing, regulations and orders, the relevant government agencies usually stipulated in various acts, enactments and ordinances carries out enforcement. Most of the non-legislative measures that include guidelines, education, research and development, planning, monitoring, and public policy are non-statutory in nature, unless they are made into laws.

Nevertheless, efforts at curbing environmental quality deterioration is beleaguered by a number of factors especially in terms of actual understanding of the physical environment, lack of inter-agency coordination and cooperation, institutional and financial shortcomings and general environmental ethics of the population.

Integrated Environmental Management System
After all the components in the first framework are set, then the second framework can be set in motion. Environmental policy should be set according to the result of interrelationship between components in the first framework. The present set of environmental legislation has to be reviewed covering all aspects of matters related to the environment.

As a matter of fact, they should be consistent and should reinforce and compliment laws and policies in other sectors. Laws and planning should be based on the policy formulated, which will lead to the formation of an integrated environmental management system. However, in the management system there should always be monitoring and review of the success or failure of the management strategies applied to ensure a balance between environment and development and likewise ensuring human security.

Conclusion
In summary, the consequences of human impact on the environment had leads to environmental quality deterioration, which in turn affect human security. Environmental management seems to be lacking behind development and even when development and management is the responsibility of the authority there seem to be a lack of coordination in the implementation of both.
It is suggested that an integrated environmental management system should be formulated taking into consideration of the physical and human environment in the country in order that further environmental quality deterioration can be checked and human security is not held to ransom. This environmental management system should accessible and continuously communicated to the consumer especially on the status of current environment quality as well future prediction so that the consumers are more alerted and appropriate action can be taken.


Answer 2(b)

Defining Sustainable Construction
The terms ‘high performance’, ‘green’, and ‘sustainable construction’ are often used interchangeably; however, the term ‘sustainable construction’ most comprehensively addresses the ecological, social, and economic issues of a building in the context of its community. In 1994, the Conseil International du Batiment (CIB), an international construction research networking organization, defined the goal of sustainable construction as “……creating and operating a healthy built environment based on resource efficiency and ecological design.” Sustainable construction is a way for the building industry to move towards achieving sustainable development, taking into account environmental, socio-economic and cultural issues

The CIB articulated seven (7) Principles of Sustainable Construction, which would ideally inform decision making during each phase of the design and construction process, continuing throughout the building’s entire life cycle. These factors also apply when evaluating the components and other resources needed for construction. The Principles of Sustainable Construction apply across the entire life cycle of construction, from planning to disposal (referred as deconstruction rather than demolition). Furthermore, the principles apply to the resources needed to create and operate the built environment during its entire life cycle: land, materials, water, energy, and ecosystems. The diagram below refers to sustainable construction framework developed in 1994 by Task Group 16.
The Seven Principles of Sustainable Construction:
Reduce resources consumption (reduce).
Reuse resources (reuse).
Use recyclable resources (recycle).
Protect nature (nature).
Eliminate toxics (toxics).
Apply life-cycle costing (economics).
Focus on quality (quality).

Reduce Resource Consumption (Reduce) – To reduce the consumption of energy during construction and operation of the building. This can lower the general conditions cost and reduce air pollution. Proper planning while installing system is required to avoid energy loss through poorly constructed systems. Poor commissioning is responsible for increased energy cost through the life of a building. Using alternative sources of power can reduce and less impact to environment i.e. green power. Small changes in lighting system can reduce energy used. Construction debris such as trees, grasses and crops and be used as an alternative fuel source through biomass technology.

Reuse Resources (Reuse) – Reusable resources normally those resources that can not be re-cycle. Copper wires can be either re-cycle or re-use. Equipment such as construction fences, traps and refillable propane tanks can be reused. Reuse can also be done for left over building supplies and materials for next job. Save excess PVC drainage piping for use on future jobs

Use recyclable Resources (Recycle) – Recycling programs, when designed properly, are cost-effective and benefit in pollution prevention. Re-cycle material not only avoids pollution but also reduces environment burden of virgin material extraction. A waste in construction can be preventing by recycling construction debris and materials (diverting waste from the landfill by recycling construction debris). This can also be to re-cycle construction materials such as concrete, wood, glass, timber, stones, drywall and carpet and carpet pad, metal and cardboard etc. Cardboard makes up the largest waste on construction sites and is one of the easiest items to recycle.
Protect Nature (Nature) – To incorporate natural system such as and protect atmosphere against emissions produced through construction processes so that able to lower the impact of construction on the site and the surrounding environment. This can be achieved by ensuring to comply with environmental laws and regulation. Another example is to minimize air pollution due to dusk and avoid open air burning.

Eliminate Toxics (Toxics) - Prevent groundwater contamination during demolition and removal of hazardous materials. Replace toxic materials with less toxic and non-toxic product to reduce hazardous packaging and use locally available materials and resources.

Apply Life-Cycle Costing (Economics) LCC - The total cost of ownership of machinery and equipment, including its cost of acquisition, operation, maintenance, conversion, and/or decommission. LCC are summations of cost estimates from initiation to disposal for both equipment and projects as determined by an analytical study and estimate of total costs experienced in annual time increments during the project life with consideration for the time value of money. The objective of LCC analysis is to choose the most cost effective approach from a series of alternatives (note alternatives is a plural word) to achieve the lowest long-term cost of ownership.

Focus on Quality (Quality) – High performance building / green building and sustainable buildings are the examples quality focus in construction. Besides that, good quality air is another quality area consideration. Good quality building is expected to minimize building maintenance cost in the long run.

Sustainable construction considers the role and potential interface of ecosystems to provide services in a synergistic fashion. With respect to materials selection, closing materials loops and eliminating solid, liquid, and gaseous emissions are key sustainability objectives. Materials in productive will be reuse and recycling rather than disposing of them as waste at the end of the product or building life cycle (close loop). Recycled materials must be inherently nontoxic to biological systems. Most common construction materials are not completely recyclable, but rather down-cyclable, for lower-value reuse such as for fill or road sub base.
In construction industry, millions of tonnes of construction and demolition waste produced annually comprise about one-third of the total solid waste stream, consuming scarce landfill space, threatening water supplies, and driving up the costs of construction. As part of the green building delivery system, manufactured products are evaluated for their life-cycle impacts, to include energy consumption and emissions during resource extraction, transportation, product manufacturing, and installation during construction, operational impacts, and the effects of disposal.

If we continue on our present path it is almost certain that current trends will accelerate. Even if we stabilize the emissions of CO² at existing levels, the position will worsen rapidly, and this could trigger certain key events such as releasing methane gas currently trapped in the Siberian permafrost, or reducing the ability of the oceans to absorb carbon dioxide. Furthermore, increasing pressure from developing countries will potentially add significantly to present emissions. The scale and rate of development in, for example, China and India is unsurpassed, but it would be totally unreasonable to expect those countries to limit their activities whereas other countries which have historically contributed much more too global emissions carry on their business as usual. This is a global problem, requiring a common approach, and all countries have a particular responsibility.

We must, therefore, recognise the need for urgent action to address this threat, and the challenge is how to reduce CO2 emissions in a way which allows continuing improvement in standards for all. This is the core of the sustainability challenge, although other issues such as caring for our physical and ecological environment also need to be considered. Neither buildings, nor products, nor materials can be described as 'sustainable', but how we build, manufacture, source and use buildings are significant factors in contributing to sustainable development. Along the construction phases, some of the important issues concerns are:
- Planning - How we build is very important but these issues are generic and independent from construction and material.
- Design – To ensure that buildings consumption of resources through occupant expected life is minimized, that the potential life of the building is as long as possible, and that there is maximum opportunity for reuse or recycling at the end of life
- Construction - To minimizing material / resource consumption, particularly of critical resources, and reducing disturbance during the building process itself. Suppliers to ensure that manufacturing processes, including transportation, are as energy efficient as possible and raw materials are sourced with minimum impact).
- Maintenance – To minimize the cost of building maintenance and servicing the building.

Many government bodies across the world have published high level policies, often with associated strategies and targets, but the biggest issue is how to realise these. This presents real difficulties because the interactions between the various issues can be complex and holistic approach is needed. However, we can still usefully discuss the major aspects separately.

Energy use - Buildings account for major energy consumption, partly through the process of construction - the so-called embodied energy, which represents the energy used in manufacturing materials and products, and the energy for transportation and site work - and operational energy, which is that used to service buildings such as heat, ventilation, light and power.

Embodied energy - Embodied energy is relatively small compared with operational energy but as buildings become more efficient in use this balance will change and embodied energy will become more important. However, as buildings become more efficient in operation, the relative importance of embodied energy will increase and we should therefore consider it carefully.

Embodied energy depends largely on the materials used and the associated production process. It can, therefore, be used to compare the environmental impact of different materials favouring those which use least energy in manufacture, delivery, etc, and therefore have the lowest global warming potential.

Comparisons of embodied impacts at a material level are generally by weight or volume. However, realistic comparison should be made based on the component or function, such as a beam or column for a given set of data. In fact, the comparisons are ideally made at the level of an assembly such as a complete floor.
When this is done, the differences are much smaller and a number of studies have shown that for complete buildings the uncertainties in embodied energy data are greater than the differences between different systems designed to the same performance requirements. The key issues are therefore 'lean design' and careful sourcing of materials rather than selecting one material over another.

There are also huge variations in embodied energy calculations depending on specific sources and methodologies, so comparisons can be very misleading. This is not helped by the 'black box' approach adopted in some software tools and much greater transparency and flexibility is needed. This will enable designers to make much more informed and precise decisions with respect to material specification and suppliers, and also encourage producers to further improve the performance.

Operational energy - The building designer is largely responsible for operational energy. They, and more importantly their clients, are recognising this and incorporating means to reduce energy for lighting, air conditioning and heating, partly by specifying energy efficient equipment, and partly by considering this as an integral part of the design.

Artificial lighting consumes a surprisingly large amount of energy and good levels of natural light can clearly help. Shading and careful location of glazing is important to avoid glare and solar gain, and reflected light, for example from exposed surfaces, can be particularly helpful in allowing deeper penetration into the interior of buildings.

Cooling is now needed in most commercial buildings because of heat emissions from equipment and occupants and solar gain. Air conditioning is very energy-intensive and much attention has been given to using natural ventilation as an alternative. This typically uses the thermal mass of the building fabric as an inverted radiator and the floor slab is the most convenient element for this, absorbing heat during the day and releasing it to the atmosphere during the cooler night.


The key issues are rather to expose the surface, which therefore needs to be visually acceptable, to encourage heat exchange through air movement across the surface, and to provide night time cooling. However, the degree of cooling which can be achieved in this way is limited, and post-occupancy studies of buildings which have used this principle reveal modest success.

For 'passive' systems, peak internal temperatures can be reduced by about 3°C, with a slightly bigger reduction if some form of forced air flow is introduced. In hotter climates, this may be insufficient to dispense with air conditioning entirely, and hybrid systems in which natural cooling are supplemented when necessary by mechanical systems are a more realistic option. Further work is therefore needed to improve performance and ensure that all design issues are adequately considered - for example to ensure that ventilation is not being restricted because of issues such as security or acoustic insulation.

Designing for long building life
Extending the useful life of a building is almost certainly better than replacing it with another. It is therefore important that the design provides for not only operational efficiency but also flexibility and adaptability so that changes in patterns of use can be easily accommodated. Long span floors, creating column-free spaces, will facilitate this. In contrast, non-structural components of a building such as finishes and services are likely to need replacing at relatively frequent intervals in which case it is important that the structural form and detail, and the interfaces between the different components, will facilitate this.

In a number of countries, new forms of construction such as post-tensioned floor slabs and cellular steel beams, so column spacings are of 15 m or more in multi-storey construction, are increasingly common and very long roof spans have been a characteristic of single storey buildings, particularly those using steel framing, for many years. Materials should also be sufficiently durable to avoid the need for replacement during the life of the building.


Designing for end of life
End of life issues are becoming increasingly important as a design consideration. Traditionally, the building has been demolished, creating vast quantities of waste. For example, in UK, this creates approximately 70 million tonnes of waste each year, the majority of which has traditionally been disposed of as landfill.

There are a few examples of complete buildings being dismantled and reused at a different location, but it is more realistic to expect that, once a building has reached the end of its life, components will be reused or materials recycled. At present, the reclaiming of structural components, such as beams and columns, for further use is very limited, regardless of the material. This is partly because of the difficulties of dismantling and separating the structural components, but it is clear that a dry form of construction is much easier to deal with. In principle, steel construction lends itself to dismantling, but clearly this depends on suitable connection details, both between steel components and with other materials. Bolted connections which are readily accessible are therefore preferred over welded details. Separating composite deck floors from the supporting beams is more difficult, and schemes which have deliberately set out to facilitate dismantling have generally used precast floor units with a non-composite frame.

There are also concerns about the provenance of elements recovered from a demolition site. At present there are major problems in identifying components and their history - essential to determine their structural capabilities - and in these circumstances most clients and designers are understandably very cautious. In reality, the practical difficulties of reuse and the attitude of most clients and designers are likely to make reuse a minority activity for the foreseeable future. It is therefore more realistic to expect that the current practice of reclaiming materials for recycling will continue and increase. Traditionally large quantities of demolition materials such as masonry and concrete were sent to landfill. However, they are being increasingly reused in other construction projects as recycled aggregate, and currently about 75-80% of such waste is used in this way.


This is principally as low quality materials for sub-base and fill, for example in road building and airfield pavements, so the benefits are more associated with waste reduction than reducing demand for virgin materials. In contrast, steel is easily recycled through its production route, with no reduction in quality, and there is a well-developed infrastructure for handling scrap steel. As a result, a very high proportion of steel is recycled, reducing the waste and minimising the demand for iron ore extraction. However, although some steel is manufactured entirely from scrap, this is insufficient to satisfy the demand, and some steel has to be produced from newly mined ore.

Materials for construction
The principal concern for product and material suppliers is energy efficiency in manufacture and transportation, but safeguarding natural resources, protecting habitats, reducing waste and minimising landfill are also important. The main issues are therefore to:
- Reduce energy and CO2 emissions in production.
- Increase use of recycled and waste materials (this also makes a positive contribution by diverting material from the waste stream).
- Use water efficiently.
Traditionally, the feedstock for the principal construction materials - aggregates, iron ore, coal and limestone - are extracted by quarrying. However, increasing use is now being made of recycled materials - scrap iron for steelmaking and recycled concrete aggregates for reinforced concrete. By-products of other industrial processes such as steelmaking, power generation and china clay production are also increasingly replacing primary aggregates. Most of these are recycled aggregates, and about 10% of demolition waste is used directly in this way. However, there are practical obstacles to increasing this such as the locations of supply and demand, the availability and quality and adverse perception.

There is also growing use of cement replacements such as granulated blast furnace slag or fly ash. Resource efficient design is also important, and off-site preparation can help minimise waste at the building site and reduces other impacts, such as noise and dust significantly. This is particularly relevant to steel construction, where modular systems, allowing complete units to be manufactured off-site, are becoming increasingly common.

The energy efficiency of the production process for construction materials and products has also improved significantly in recent years, with associated reductions in CO2 emissions. For cement manufacture, alternative kiln fuels such as waste tyres and inert processed sewage pellets are being introduced. Techniques such as continuous casting have also led to dramatic savings in the manufacture of steel products.

Life cycle assessments
Even this brief overview highlights the complex interacting issues involved in considering sustainable construction. Many of these are qualitative rather than quantifiable, and it can be very difficult to develop detailed methods which will inevitably lead to sustainable solutions. However, simply considering sustainability as an important goal is a major advance. Even in the case of a single impact such as energy consumption there are interactions - between embodied and operational energy - and what is important is that the whole building is considered over its full life cycle.

This is an unfamiliar and complex process for most building designers and commercial software is being developed for use in this field. Such computer-based design aids include assessment tools which 'score' a building against a range of potential impacts, and as the government starts to develop a code of practice for sustainable buildings it is likely that such assessments will become integrated into the design process.

Conclusion
The rapidly evolving and exponentially growing green building movement is arguably the most successful environmental movement around the world mostly in Europe today. In contrast to many other areas of environmentalism that are stagnating, sustainable building has proven to yield substantial beneficial environmental and economic advantages. Despite this progress, however, there remain significant obstacles, erected by the inertia of the building professions and the construction industry and compounded by the difficulty of changing building codes.

Industry professionals, in both the design and construction disciplines, are generally slow to change and tend to be risk-averse. Likewise, building codes are inherently difficult to change, and fears of liability and litigation over the performance of new products and systems pose appreciable challenges. Furthermore, the environmental or economic benefit of some green building approaches has not been scientifically quantified, despite their often intuitive and anecdotal benefits. Finally, lack of a collective vision and guidance for future green buildings, including design, components, systems, and materials, may affect the present rapid progress of this arena.

Despite these difficulties, green building movement continues to gain momentum, and thousands of construction and design professionals have made it the mainstay of their practices. Numerous innovative products and tools are marketed each year, and in general, this movement benefits from an enormous air of energy and creativity. Like other processes, sustainable construction may one day become so common that its unique distinguishing terminology may be unnecessary. At that point, the green building movement will have accomplished its purpose: to transform fundamental human assumptions that create waste and inefficiency into a new paradigm of responsible behavior that supports both present and future generations.

Sustainable construction can be considered as a subset of sustainable development in which economic growth and social progress for all is coupled with effective protection of the environment and prudent use of resources. It is becoming so important because of concerns about damage to our environment through climate change brought about by global warming, and recognition that natural resources are finite.

This is further accentuated by the rapid economic growth in a number of highly populated areas of the world, significantly increasing the potential environmental impact globally. The social dimension of sustainability is associated with the right of everyone to equally high living standards - and climate change is a global issue. So we must all accept a share of responsibility. Pressure is therefore mounting on industry, including the building sector, from both legislation and public perception to change the way we operate.

Construction has been identified as being particularly important because of the significant environmental and social impacts which the built environment has on everyone's quality of life. It is estimated that, on average, we spend 90% of our lives in buildings. Whether at home, at work, in education or at leisure, everyone uses, and indeed relies on, the output from the construction industry. Furthermore, people's performance and productivity can be enhanced by improving the quality of the buildings in which we live and work.

But the negative impacts are also significant. Construction is a major consumer of raw materials (including energy), and accounts for a high proportion of waste. Each year in the UK the construction sector consumes over 420 million tonnes of a wide range of raw materials and generates about 94 million tonnes of waste -∼13 million tonnes of which is estimated to be due to over specification. The manufacture of cement alone accounts for over 2% of all CO2 emissions in the UK (The UK Construction Industry 2003). There is accordingly a growing interest in using recycled materials and even reusing components.

Buildings are also major consumers of energy, accounting for approximately 50% of all energy used; energy efficient building design is, therefore, very important. Even in the UK, commercial buildings need cooling rather than heating for most of the year and natural cooling systems are becoming more popular. These generally use exposed parts of the building's structure with significant implications for design and construction