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The building industry is, after food production, the largest consumer of raw materials in the world today. A broadly accepted goal for a sustainable future is a drastic reduction in the use of raw materials. This is most important for the scarce non-renewable resources but also for the others; partly because it is the throughput of materials in the economy that is linked to major energy and environmental loads. Equally important is reducing wastage and losses during production, the construction process and throughout the life of the completed buildings. The recycling of materials following demolition must also become the rule. Recycling processes should also ensure that materials can be taken care of at their original level of quality, rather than downcycled.

1.1.1 Actions for resource conservation in the production of materials

Change-over to exploitation of smaller deposits of raw materials

This is mainly a question of technology. Even though modern technology is primarily geared to large-scale exploitation ('economies of scale'), viable smaller-scale alternatives often exist. Small-scale exploitation is often far less damaging to the environment, in particular as regards water resources and biodiversity.

The cycle of materials.

Greater attention to unused resources and waste products

Many resources that were formerly classified as 'uneconomical', and now fallen into disuse, and others that have not previously been used, need to be studied. Examples of such resources are compressed earth used as a construction material; fibres from the seaweed eelgrass as an insulating material; and increased use of timber from deciduous trees.

The same applies to an increasing number of 'waste' products from industry, agriculture and dwellings, such as straw, fly ash, industrial sulphur and waste glass.

Substitution with less limited types of resources

Many raw materials are not in danger of exhaustion in the foreseeable future. An example is stone, which is still plentiful in most places. Another is blue clay, which has great potential and is in no way near being exhausted by the small existing production of clay bricks.

Substitution with renewable resources

Many building components currently made from non-renewable raw materials have renewable alternatives. For example, timber can be used as an alternative to steel. A wide range of plastics can be produced from plants instead of fossil hydrocarbons. This type of substitution will usually have a positive overall environmental impact.

However, we must beware of the risk of increased use of renewable resources in construction coming into conflict with food production. Seen in the global perspective, with a rising population, one should give first priority to waste products from agriculture and plants that can be grown in relatively unproductive land areas - as is the case with most timber species.

Increased recycling of waste products during production

For reasons of simple efficiency and cost, many good examples, showing how the recycling of waste products during production can save valuable resources, already exist. For example, in the plasterboard industry today waste has nearly been eliminated in the production process. Re-use of water in the production processes of certain industries also occurs more often; for example, in the production of ceramic tiles and wood fibre boards.

1.1.2 Reduction of the use of materials in the building

'Do we really need to build this at all?' should be a basic question if one wishes to reduce the use of resources in construction. It is, however, seldom appreciated by any of the parties involved in design processes. The obvious second question is then 'How can we reduce the need for materials?', and here a whole range of possibilities emerge.

Reduce the need for materials, adaptable buildings

Space use per person has doubled in the western world since 1960. In housing, each of us now consumes 40 to 50 square metres (Berge, 2003). This implies an approximate doubling of the consumption of materials. At the same time, both housing and other types of building have become more specialized, being tailored and optimized for specific functions. In most cases they are becoming far less flexible or adaptable.

This static approach, in a society characterized by rather rapid changes both in cultural patterns and technology, means that buildings are often demolished well before their intended lifetime is over. Initial lifetime projections (service life predictions) are often incorrect. In Sweden, 25% of the buildings that have been demolished since 1980 were less than 30 years old (Thormark, 2007). In Tokyo the average lifetime of a building has been as low as 17 years in periods of high economic activity (Brand, 1994). Expected climate changes will make this picture even worse. Considerable areas of land may become uninhabitable due to sea level rises as well as increased risks of flooding and landslides. Higher temperatures may increase the need for solar shading, cooling technology and insect protection measures, all requiring building modifications or replacement. Increased precipitation or more frequent temperature variations may also lead to accelerated decay of building envelope materials.

Our response to these scenarios has to be a requirement for buildings that have an increased adaptive capacity. This relates not only to the technical systems, but also to planning aspects, where the following principles need to be addressed:

• Generality: spaces allowing for a broad range of activities.

• Flexibility: buildings permitting easy changes to floor plans as well as to the technical systems.

• Elasticity: designs permitting expansion as well as contraction of buildings. Extreme elasticity implies buildings with short lifetimes of say 10-15 years that can be easily dismounted, reprogrammed and reassembled.

All the above necessitate new and appropriate design and construction methods, in order to allow for change and the avoidance of extensive waste of materials usually associated with the modification and demolition of buildings.

It has been estimated that such solutions can increase real building lifetimes by 25% in 25% of all buildings (Kram, 2001). Optimizing buildings in this way also reduces overall space needs and therefore also the energy consumption for heating, cooling, lighting and ventilation. This kind of approach is probably more efficient than today's conventional approach of reducing energy use by superinsulation, solar panels and heat pumps.

Economical use of materials

Any given structural system requires a specific amount of materials, and the difference between systems can be quite significant. As the best engineers know, the amount of material used in a steel column can be reduced several times by optimizing the design; and a lattice beam uses much less material than a solid beam, whether it is timber or steel. Other typical examples are hollow bricks and aerated concrete blocks instead of massive products. Again, due to increasing resource and cost constraints this kind of efficiency is in full progress.

A choice of lightweight constructions rather than heavy alternatives, such as timber instead of concrete, also significantly reduces the need for foundations. On difficult sites such as waterlogged or clay areas, it has been calculated that the use of a lightweight construction can reduce the use of concrete footings from 250 to 150 kg/m2 (Gielen, 1997).

Minimizing materials losses and wastage on site

Every material has a 'loss factor', which describes how much of a particular material is typically lost during storage, transport and installation of the final product.

Loss of materials on site is approximately 10% of the total waste in the building industry. This can be halved with carefully planned site management (Thonvald, 1994). Timber and other off-cuts can be sorted and re-used elsewhere. Using loose fill insulation avoids the often considerable wastage of insulation off-cuts. Prefabrication provides even greater savings, where almost all wastage can be eliminated either through pre-cut components or prefabrication of whole elements. In Scandinavia today almost 80% of all new housing units are produced off-site. One should remember, however, that some prefabrication systems necessitate extensive use of jointing mastics or gaskets that may have unfavourable environmental characteristics.

Within the building industry, a great deal of packaging material is used during transport and for storage on site. Some packaging serves no greater purpose than to advertise the name of the supplier. If nothing else, packaging should be easily recyclable and therefore should not comprise materials such as aluminium and plastic composites.

Loss of material caused by wear and tear in the completed building will also occur. The Swedish Department of the Environment estimated in 1995 that the loss of copper from roofs and pipes through weathering amounted to more than 1000 tons per year. In addition to the resulting pollution, this represents a large loss of resources. Materials based on rare, non-renewable resources should thus preferably not be used in exposed parts of the building.

Use materials in ways that ensure their durability

It is important to match the resource quality to the task required, so as not to use a high-grade resource when a lower grade one will suffice. But it is still a general rule that by producing more durable products the use of raw materials is reduced. However, one must ensure that materials of similar durability are used throughout the vital parts of a building; therefore not sacrificing high quality components due to rapid decay elsewhere. Lower quality materials should be used in such a way that they are easily replaceable, whilst more durable materials may be easily dismantled for re-use or recycling.

Simply put: twice as much damage to the environment can be tolerated for a product that lasts 60 years compared to one that lasts only 30 years. The lifespan of materials is governed mainly by four factors:

• the material itself, its physical structure and chemical composition.

• the local environment, climatic and other chemical or physical conditions.

• the construction and its execution, where and how the material is fitted into the building.

• maintenance and management.

The lifespan of a roof tile, for example, is dependent not only on the type of clay used, but also on the immediate environment of the building. A high moisture content in winter can cause frost damage even in high quality tiles. The best way to determine the real lifespan of a material is through long experience and concrete documentation. It is therefore difficult to anticipate the lifespan of many new materials, such as new types of plastics. It is possible to perform accelerated deterioration tests in laboratories, but these generally give a simplified picture of deterioration processes, and results can only be taken as approximate.

During construction, many materials are exposed to rain or humidity. Sealing damp materials into buildings is a principal cause of subsequent defects, as well as posing a well-documented health risk. Adjoining building components may also be damaged. Careful site management routines and storage are recognized today as an important preventive solution. Other solutions include construction systems where the load bearing structure and roof covering are assembled first, and construction canopy systems, usually called Weather Protection Systems (WPS).

Construction systems also need to protect materials during their lifetime from stresses (arising from within or without) such as undue temperature and humidity conditions. An important aspect of this is due adaptation to local climatic conditions, not always the case in an industry that uses standardized solutions regardless of regional climatic differences. This applies in particular to high value items such as doors, windows and balconies, as well as to appropriate roof detailing. A major investigation was made in 2001 of 16 000 buildings in Denmark, including single-family houses, apartment blocks, offices and schools (Valbjorn and Eriksen, 2001). It showed that buildings with flat roofs had twice as high a risk of serious humidity damage. Bathrooms with timber based wall and floor structures had twice as high a risk as those in masonry and mineral materials (see Figure 14.6 in Chapter 14).

In order to reduce energy consumption and climate emissions, most temperate and cold climate countries are introducing ever stricter norms for increased thermal insulation of buildings. In some cases, this has led to increased humidity damage - partly because less heat from inside the building actually leaks out into the walls to dry out any humidity that may have gathered there. This means that there is a higher requirement for precision in both the detailing and execution of highly insulated, low energy buildings. This will not be easy to achieve. For this reason it would be a major advantage if one can employ materials with good hygroscopic qualities - materials that can tolerate and regulate humidity.

We should also remember that durability is not only a quantifiable technical parameter. Durability also has an important aesthetic aspect. It is quite a challenge to design a product that can outlast the vicissitudes of both time and fashion.

On the other hand, there is a point where long-lasting buildings become an economic or environmental burden; it becomes difficult to upgrade or adapt them any further, and their replacement would save resources due to technological advances and efficiency gains. The resources saved by continuing to use an old, energy consuming building have to be weighed against the new materials needed to build a replacement building that can save much energy over the following 50 or 100 years. Comparative lifecycle assessments can be made to inform such decisions. The key question is thus optimum rather than maximum durability.

The decay of building materials is also a health issue. Decay of building sheets and tiles containing asbestos releases the toxic fibres into the environment; decay over time of bathroom boards exposed to prolonged dampness can also increase off-gassing and release of synthetic chemicals into the rooms. Material decay can also increase the danger of fungal growth and other harmful agents into the indoor environment, causing increased allergic or respiratory ailments.

DURABILITY AND CLIMATE

Although we do not know all factors affecting durability, the following climatic parameters determinethe lifespan of a material to a large extent:

Solar radiation. Ultraviolet solar radiation deteriorates organic materials by initiating chemical reactions within the material and causing oxidation. This effect is stronger at high altitudes where the ultraviolet radiation is more intense, and it also increases toward the equator.

Temperature. An old rule of thumb is that the speed of a chemical reaction doubles for every10 °C increase in temperature. Higher temperaturestherefore increasethe deterioration of organic materials. Emissions of formaldehyde from chipboard containing urea-based glues are doubled with every 7 ° C increase of temperature. Heat also stimulates deterioration processes in combination with solar radiation, oxygen and moisture.

At low temperatures, materials such as plasticand rubber freeze and crumble. A porous low-fired brick only lasts a couple of winters in northern Europe-whereas in the Forum in Rome the same brick has lasted 2000 years. Above all the cycle of freezing and thawing is a deciding factor for most porous mineral materials.The coastal climate ofthe North is also very deleterious.Wide changes intemperaturestrain materials, even without frost, and will cause deterioration.

Air pressure. Air pressure affects the volume of and tensions within materials that have a closed pore structure, such as foam glass and various plastic insulation materials. Sealed windows will also react. Changes in size thatoccur havethe same effect as temperature changes.

Humidity. Increased humidity can increase deterioration both physically, and by creating an environment for harmful fungus and microbial growth as well as insect attack. Changes of humidity also cause deterioration through changes in volume and stresses within the material. This is why the manufacture of musical instruments such as pianos and violins can only take place in rooms with a very stable air moisture content. The same stable conditions should ideally also be applied to building interiors in order to reduce the deterioration of surface materials and to facilitate cleaning.

Urea-based chipboard, mentioned above, doubles its emissions not only with temperature changes but also with an increase of 30-70% in relative humidity.

Wind and rainfall. Conditions are at their worst when wind and rain come simultaneously. Then dampness can be driven into the material and start the deterioration process. Strong winds cause pressure on materials that may even lead to fracture or collapse.Wind combined with sand or sea saltcan have a devastating effect on certain materials.

Chemicals. Along the coast the salt content of air can corrode plastics, metals and certain minerals. In industrial areas and in the vicinity of heavy traffic, aggressive gases such as sulphur dioxide can break down a variety of different materials. Concrete suffers from so-called 'concrete sickness' where the calcium content is broken down in aggressive environments. This also occurs with certain types of natural stone - as witnessed in the deterioration of many ancient monuments due to modern pollution.

DURABILITY IN THE PERSPECTIVE OF GLOBAL WARMING

Global warming will change materials behaviour significantly. Most regions can expect increased temperatures and in particular, periods of more extreme heat. Many regions are expected to become wetter. This will often occur in combination with increased winds, such as in northern Europe and northern parts of Asia.These regions will also experience more frequent freeze-thaw cycles.

These circumstances will accelerate decay in porous stone, concrete and rendering materials. In Scandinavia an increase in mould growth on organic materials of 50% is anticipated within the next century. Rates of corrosion in metals will increase (Noah's Ark, 2007). On the other hand, in regions such as southern Europe, drier

Relative changes in precipitation (in percent) for the period 2090-2099, relative to 19801999. Scenarios are for December to February (left) and June to August (right), (IPCC, 2007).

Relative changes in precipitation (in percent) for the period 2090-2099, relative to 19801999. Scenarios are for December to February (left) and June to August (right), (IPCC, 2007).

conditions may increase damage due to differential thermal expansion and contraction in organic as well as inorganic materials. Migration of destructive insects such as termites may also cause new problems in regions where buildings have never been designed with this in mind.

In some regions climate change may bring decreased risks. In central Europe and the United Kingdom, no great changes are expected in the climatic stresses on building materials. With the exception of the Alpine region, the risks of fungal attack as well as frost damage may in fact, decrease.

A further factor is likely to be rising water tables, affecting soil chemistry and hence foundation conditions. Rising sea levels and flooding can also cause widespread humidity damage. Here too, future material choices need to be considered for theirdrying ability and retention of pre-flood properties (Escarameia, 2007).

Building and material decisionsthus need to take into account climate scenarios for any particular region. Regional climatic variations are likely to be large; there is therefore a high level of unpredictability in this. As a general rule, however, organic materials need to be given better protection and more robust materials will be needed.

Maximizing recycling

Every material has a resource footprint and a pollution footprint, particularly during production. Much of this can be avoided by recycling products rather than manufacturing from new raw material. A product that can be easily recycled will normally be preferable to a product that is initially quite 'green' but cannot be recycled.

In the building industry many current products and materials have both poor durability and a low recycling potential. There are others that can be recycled several times but in many cases this is seldom done.

Recycling and re-use are more widespread in Holland than in most other industrialized countries. Legislation requires that 80% of demolition materials be recycled into new construction, either buildings or other civil works such as road building. When tendering for contracts, demolition companies have to state how much of the material will be recycled, together with a presentation of how they will do this. There are examples of successful demolition projects where different materials and products have been separated, and a level of up to 95% recycling has been achieved (Holte, 2005). The buildings demolished are often older types with a fairly simple use of materials. For modern buildings, it is doubtful whether the level of recycling can exceed 70%. As a rule, modern buildings also contain larger fractions of problematic, composite or hazardous components that are far more difficult to handle and recycle.

There are also a few examples of successful projects in which whole new buildings have been built composed mainly of recycled materials (Crowther, 2003; Addis, 2006).

However, it is worth remembering that even an ambitious recycling policy is limited by the ratio of new building production to demolition of old ones. At present this ratio is about 4:1 in Western Europe, meaning that recycling can, at most, supply only a quarter of the market for new building materials.

THE DIFFERENT LEVELS OF RECYCLING

Seen from the perspective of industrial ecology, waste can be defined as resources in the wrong place - resources that have gone astray. The goal is to bring all resource flows back into a closed loop where they circulate within the human economic system, so that extraction of new raw materials as well asf inal discarded waste becomes an absolute minimum (McDonoughand Braungart,2002).

In addition to this principle, there are different levels or degrees of re-use and reprocessing. A range of terms are used to define these levels; however, the three principal ones are (in hierarchical order):

A: Re-use B: Material recycling C: Energy recovery

Re-use means the use of a whole component, in largely unchanged form and for a similar function; for example a brick re-used as a brick.

Development of re-usable structures and components has not yet come very far. There are few quality control routines for re-usable products. Efficient re-use of materials or components demands simple or even standardized products. Very few products on the market today meet these requirements. In highly industrialized countries there are as many as 300 000 products in the building industry, all with different designs and composition. At the same time, most buildings are not designed for easy decon-struction.This implies a large riskof damaging the products when buildings are demolished. However, new methods of design for salvageability are emerging slowly (Fletcher, 2001; Addis, 2006; Durmisevic, 2006; Nordby etal., 2007).

Historically, re-use of building materials was a normal feature. In many coastal areas old buildings were constructed using a great deal of driftwood and parts of wrecked ships. Nordic log construction is a good example of a building method geared for reuse. The basic principle of mounting robust logs on top of each other, with joints not nails, makes them very easy to take down and re-use, totally or in parts, as well as to move whole buildings to a new site.This building method uses a large amount of material, but the advantages of re-use balance this out.

Material recycling means melting or crushing the component and separating it into its original constituent materials, which then re-enter the manufacturing process as raw material. This is an efficient solution for metals. For other materials, different degrees of downcycling lead to products where part of the original value is lost, for example reducing high quality plastic articles to flower pots, or crushing lightweight concrete blocks into aggregate.

The potential for material recycling is also highly dependent upon the purity of the item, since separation of different constituents may be diffcult, hence costly or near impossible in the case of quite a few composite building components.

Where productsclaim to havea potential for material recycling, the statement is often based on theoretical figures. In practice there are often complications: thin aluminium containers often burn up totally or evaporate when being melted; in the worst cases,

A traditional summer village on the south coast of Turkey. The huts are made of driftwood, packaging and other available free material.

A traditional summer village on the south coast of Turkey. The huts are made of driftwood, packaging and other available free material.

small amounts of impurities in waste products can lead to a need for extra refining processes and a higher use of energy than for new raw materials.

Energy recovery means burning the demolished product to produce energy. Here, all the original raw material resource is lost and only its energy content is recovered. It is therefore a lower grade of recycling. This is, however, clearly a very economical and even profitable way to treat many forms of waste. It is especially advantageous if the materials can be burned at a local energy plant, to reduce transport energy; and if the waste-to-energy products do not contain toxic residues requiring complicated flue gas treatment.

DESIGNING FOR SALVAGEABILITY

An optimal environmental choice is a building with high adaptive capacity designed for easy maintenance, disassembly and re-use of constructions and components. The following are basic principles.

FIRST PRINCIPLE: SEPARATE LAYERS

A building consists of several parallel layers (systems): interior, space plan, services, structure, skin (cladding) and site (see Figure 1.4). The main structure lasts the lifetime of the building - 50 years in Norway and Britain and closer to 35 in the USA (Duffy, 1990) - while the space plan, services, etc. are renewed at considerably shorter intervals. In modern buildings the different layers are often incorporated in a single structure. Initially this may seem efficient, but the low in the long-term cycles will then block the short-term cycles, and short-term cycles will demolish slower cycles via constant change. It is, for example, normal to tear down buildings where installations are integrated in the structure and difficult to maintain.

We need a smooth transition between layers, which should be technically separated. They should be accessible independently at any given time. This is a fundamental principle for efficient re-use of both whole buildings and single components.

The main layers of a building. Source: Brand, 1994.

SECOND PRINCIPLE: POSSIBILITIES FOR DISASSEMBLY WITHIN EACH LAYER

Single components within each layer should be easy to disassemble. Figure 1.5 shows three different principlesforassembling a wall cladding at a corner.The shading shows where the mechanical wear and tear is greatest, from people, furniture, wind and weather. The normal choice today is the first solution, (a), where all parts are of similar quality and permanently connected. When the corner is worn, the whole structure follows with it. In many expensive public buildings, solution (b) is chosen. By increasing the quality of the most exposed parts, the whole structure will havealongerlifetime.This is usually an expensive solution and makes changes in the space plan difficult. In solution (c), fast wearing parts can easily be replaced separately. The used component can even be re-used in another place where the aesthetics are less important, or it can be sent for material or energy recycling.

THIRD PRINCIPLE: USE OF STANDARDIZED MONOMATERIAL COMPONENTS

Before re-use of the components it is necessary to check their quality. This often presents problems. Many building components are composed of different materials laminated together (see Figure 1.6). Re-use of such products is difficult. Different rates of decay within the same component may result in one of the materials being partially decayed whilst the others are still in good condition. This problem is especially acute in large, prefabricated building elements where cladding, insulation and structure are integrated in a single component.

For re-usable structures only so-called primary and secondary monomaterials should be used. A primary monomaterial is a single homogeneous material used in its natural state, for example untreated wood. A secondary monomaterial is a mixed material of homogeneous nature, e.g. concrete, glass or cellulose fibre. By only using monomaterials it is usually easy to check its quality for re-use.This will be even easier if materials are supplied with an identification code with information on type and application.

Three constructional concepts for a corner.

Three constructional concepts for a corner.

Even if re-use products are thoroughly quality controlled, there still may not be a market for them. The shape of the components may be so unusual that they would need to be transported some distance to find a buyer. So this whole strategy can quickly become an energy problem. Re-usability is therefore also determined by the generality of components.

Most components of buildings could in principle be designed for re-use in this way, though some, such as electrical installations and other technical features, may be inherently less suitable for re-use, in particular since totally new technology may have become current.

(a) Multimaterial component; (b) monomaterial component.

At all levels of recycling there will be some waste. Even when full recycling is done, there are still materials left over which need to be taken care of. This can be a large fraction if the material quality is poor to start with, as in the case of waste paper pulp that has already gone through several rounds of recycling. Alternatives in such cases are dumping or global recycling. Global recycling means composting the materials, or in some other way biodegrading and reintegrating the materials into nature. For example, when cellulose is composted, it is first covered by earth; a series of complex biological processes follow in which mould deteriorates the cellulose structure. Special enzymes in the mould release carbohydrates that stimulate bacterial growth which in turn attacks the molecular structure of the cellulose and releases soluble constituents of nitrogen. The end product is humus, thus becoming a new resource for different plant organisms, providing nutrients for the growth of new cellulose fibres.

In this way global recycling is based almost entirely on closed cycles, which means that there is hardly any waste. These methods can also be considered a more sensible way of depositing a material compared with ordinary material recycling or energy recovery.

Designing buildings almost entirely based on easily biodegradable materials can reduce demolition waste to a minimum (Sassi, 2006).

However, many biodegradable materials available for building today have some form of additives or chemical treatment.

1.1.3 Raw materials in a world context

Most of today's global consumption of materials takes place in the northern temperate zone. But that doesn't mean that most are produced in this part of the globe. Throughout modern times most mineral and fossil resources have come from the so-called developing countries. This is, however, changing rapidly. Today, 70% of exports from these countries - in particular from Asia - consist of refined or value added products (Achear, 2006).

Although most consumption continues to be in the North, industrialization is accelerating in the South, not least due to considerable relocation of our industries there in order to exploit cheaper labour and energy prices, lower environmental requirements and other advantages. This trend applies in particular to clothing, cars and electronics. For the present this seldom includes building materials, partly because long distance transport of heavy items is costly. There are, however, already exceptions; for example, chemicals used in the plastics industry, such as phosgene which is the base chemical for polyurethane. This could be prohibitively expensive to produce in Europe due to environmental legislation. The same applies to labour-intensive construction materials, such as granite and marble products that today are often cheaper to import from as far away as China.

Beddington Zero Energy Development (BedZED) in Surrey (UK) with extensive re-use of timber, steel and brick. Building materials were selected from renewable or recycled sources within 35 miles of the site, to minimize the energy required for transportation. Bill Dunster Architects, 2002.

Beddington Zero Energy Development (BedZED) in Surrey (UK) with extensive re-use of timber, steel and brick. Building materials were selected from renewable or recycled sources within 35 miles of the site, to minimize the energy required for transportation. Bill Dunster Architects, 2002.

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