Materials: Intro and Criteria for Materials Selection

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For all peoples, and certainly for those of us who live in a cool climate, shelter is one of the basic needs of life, along with food, water, and air. However, the way in which we select and use building materials has a profound effect on our homes and environment. If we care for the environment, we can't delegate responsibility to a designer, architect, or builder for choosing materials unless we can trust them to specify ones that fulfill certain ecological criteria.

On a global basis, the sheer amount of raw materials being used up is staggering. The world manufactures eight times the volume of goods it did in the 1950s; yet this increase has not taken place evenly around the globe. Now that previously low-growth regions of the world are beginning to expand production very rapidly, under the influence of the West, the world wide demand for resources is being stepped up still further. The Far East, especially China with its enormous population, is a case in point. We not only have a population explosion, but we have an even greater production and consumption explosion to go with it! The impact on our environment is devastating In the US and UK, as in most of the Western world, it is increased personal consumption that is the main cause of this increased volume of production. We live in a growth economy where there is always the underlying assumption that it is good to increase the size and quantity of personal possessions, and to improve their quality. There are many examples of these continually increased expectations: from refits for kitchens, bedrooms, and bathrooms to ever more cars, demanding ever more road-building.

What is worse, we now use materials in far more wasteful ways than ever before. Wastage on building sites often amounts to around 20% of materials; and then there are the mountains of refuse that come out of our homes every week. It is only our short-lived energy glut and unsustainable growth patterns that are allowing us to waste on such a massive scale.

There is much that we can do to turn this tide. The rise of “green consumerism” has shown that together we have an economic power to affect ecological change. First we need to become well informed on the criteria for choosing particular materials or appliances. We need the will and the determination to make decisions independent of “the Joneses” and of TV advertising. We need to know when not to buy but to clean up and repair whatever it was that we were going to replace. However, in order for us to behave in an ecologically responsible manner, we also need accurate and relevant information from manufacturers.

To provide information, manufacturers also need to have the right priorities and the incentives to produce ecologically. We ourselves as consumers can provide these incentives by supporting those companies that are heading in the right ecological direction. Some progressive businesses are now beginning to realize that they have little choice in the long run but to manufacture products that are environmentally acceptable. We have to create a climate in which companies will not succeed if they have a careless approach to the environment.

New ecological standards are required. There are clear national and international standards in terms of strength, safety, durability, and so forth regarding the quality of particular products. However, standards and information relating to the environmental impact of consumer goods are more difficult to measure and are rarely given as part of product information. In addition, some early attempts at green labeling systems got off to a bad start. Now the European Community is starting a new labeling system, with each country developing standards for different materials and appliances. We await the results of this new initiative with interest. However, we need never wait for governments to act before acting ourselves.

The first section starts with a look at the different criteria that we can apply to help us choose between different materials. The materials them selves are then analyzed, starting with the renewable materials, which are taken mainly from the plant world, followed by mineral resources, and ending with a look at synthetic and processed materials.

The consumer revolution has had many effects, most of them detrimental to the environment. Now we need a greening of this consumerism and , above all, less consumption.

Criteria for Materials Selection

What criteria should be applied when selecting materials for incorporation into an ecological design or renovation? This section aims to answer this question by briefly elaborating on ten chosen attributes. Ecological building materials are those that comply with most or all of the criteria listed below. In many cases it will be a matter of finding a material that provides the best balance among the ten different criteria.

• Clean—nonpolluting in terms of:

  • global warming
  • ozone depletion
  • acid rain
  • ground and water pollution

• Healthy to humans and domestic animals—most commonly natural or inert materials

• Renewable—usually products of living organisms, such as trees

• Abundant—of almost inexhaustible supply, for instance, certain kinds of rock

• Natural—since highly processed or synthetic materials tend to waste more energy and raw materials

• Recyclable—reusable or biodegradable

• Energy-efficient—low embodied energy consumption in the production process

• Locally obtained—often part of vernacular building traditions

• Durable—reducing the need for frequent replacement

• Design-efficient—favorable for flexible, safe, and efficient design


In this category, nonpolluting refers to those materials which cause a minimum amount of damage to the earth’s ecosystems. The materials excluded from this category are those which cause atmospheric pollution, in particular those gases and vapors that cause global warming, ozone depletion, and acid rain. In addition to atmospheric pollution, there are those materials which cause the pollution of the ground, rivers, lakes, and oceans. Each of these different types of pollution is briefly analyzed below.

Greenhouse Gases

Greenhouse gases have already been referred to in the ENERGY sections. The most important are carbon dioxide, methane, nitrous oxide, and the chlorofluorocarbons (CFCs). Materials containing CFCs are looked at under ozone-depleting chemicals below.

Most materials are responsible for some carbon dioxide (CO2 emissions; it is possible to evaluate all materials in terms of tons of CO2 produced per ton of material. It is then possible to calculate the total amount of CO2 produced per building component or appliance. There is a rough correspondence with embodied energy (see ENERGY-EFFICIENT section below).

Methane is now being taken more seriously as a greenhouse gas. It is caused by a number of factors, which mainly relate to agricultural practices. However, a growing proportion of methane is given off from garbage dumps where anaerobic decomposition takes place. This gives us a further reason to be more aware of what happens to our household waste, including our sewage, when it leaves our homes.

Nitrous oxide (NO2) pollution is caused by nitrogen-based fertilizers, fossil fuels, and the burning of biomass. It is thus mainly an energy-use issue, in terms of building materials (see the ENERGY-EFFICIENT section).

Ozone-Depleting Materials (CFCs)

It is now widely accepted that ozone depletion is a serious threat to our environment, but its ultimate consequences are as yet unpredictable. Besides causing ozone depletion, the CFC-12 molecule is 10,000 times more damaging as a global warming agent than a CO2 molecule. On the basis of these two effects, it seems only sensible to eliminate CFCs as completely as possible from further use.

There are four ways that CFCs are commonly used in domestic building:

• As the expanding gas in insulants such as polyurethane foam. CFCs could be replaced in many cases by carbon dioxide, helium, or argon.

• In refrigerators, where the refrigerants can now be replaced by a mixture of propane and butane. Refrigerators using this mixture are now on the market.

• As propellants in aerosol sprays such as paint or foam; carbon dioxide, helium, argon, and even propane in certain circum stances can be used instead.

• In fire-protection equipment (halon), which can mainly be replaced by carbon dioxide.

Since, increasingly, there are perfectly reasonable alternatives to products containing CFCs, there is no need to buy building materials that use them.

Acid-Rain—Causing Chemicals

There is some uncertainty as to whether coal-burning power stations or the agricultural use of sulfates is more to blame for acid rain. Whichever it is, it seems sensible to reduce the pollution from both these sources. The following list gives the acids and their main sources:

• Sulfuric acid, produced by sulfur dioxide emissions from power stations and fertilizers being broken down in the sea

• Nitric acid, produced by nitrogen oxides in combustion gases

• Formic acid, produced by methane oxidation (see methane, above)

As can be seen from the above, in terms of reducing acid rain that can be ascribed to the use of building materials, we need to be aware of which building materials produce quantities of these gases either directly (as in brick making or cement production) or indirectly through high-energy processes (see the ENERGY-EFFICIENT section).

Ground- and Water-Polluting Materials

Products that produce ground contamination or degrade the earth’s “skin” include those involving the destructive extraction of raw materials, including deforestation. In many cases, groundwater is polluted in the process.

In the WATER section, mention has been made of some of the most important water-polluting chemicals. Although industrial agriculture is the biggest polluter of water, through its use of synthetic pesticides and fertilizers, industrial processes run a close second, and it is here that we need to know a lot more about the water-polluting nature of different processes. Nearly every industrial process uses water at some point: it is simply a matter of how much water is used and the total amount of pollutant that is leaked into the environment (into groundwater, rivers, lakes, or oceans). Many paints, for instance, are water-polluting, containing substances such as cadmium, which has largely replaced lead as the pigment in brilliant white paint.


This subsection also deals with pollution, but of a different type. Here our concern is for personal health rather than the health of the planet. The main issues have already been studied in the early sections of HEALTH. However, it might be useful to understand the difference between a hazard and a risk, in relation to health. Lead, for instance, is a hazardous material, but the risk of it proving a danger to our health depends on where it is found, the quantity of it, the likelihood of it contaminating our food and water supply, and so on. It is therefore possible to have a small quantity of a very hazardous material in a safe and secure location posing very little risk, whereas a much less harmful material that is everywhere in the house, such as PVC (polyvinyl chloride, a constituent of most paint and many plastic household products), could actually pose a greater health threat. If in doubt, use an obviously benign material if one is available. For instance, if you are buying a carpet and have the choice, it is safest to buy one made from natural materials such as cotton, jute, or wool.

On dangerous chemical containers there should be a “hazardous product” safety notice. Take these notices seriously and read them carefully. Only use such products if there is really no alternative.

Besides diet, exercise, and lifestyle, the most important health influences encountered in the home are the materials that come in contact with our bodies, and those found in the air we breathe. Contaminants from building materials in the home that affect personal health include asbestos, organo-chlorines, dust from treated timber, formaldehyde, lead, phenols, and volatile solvents; there are also the products of combustion, household cleaning, maintenance, and pest control (see TOXINS).


The only materials that are truly renewable are the products of living organ isms, which use energy directly or indirectly from the sun and are made up from compounds that are continuously recycled in the biosphere. Although there are some such materials that are the products of animals, such as leather, silk, and certain glues, the main source of these materials is the plant kingdom.

It is also generally accepted that labor can be seen as a renewable resource. This is one of the features of ecological thinking that results in very different analyses, when compared with conventional economic thinking.

There is an important difference between fast-growing plants that provide easily renewable materials and those that are rare or slow-growing. A genuinely renewable resource should feature a harvesting cycle related to its replacement growth. In other words, trees that take a hundred years to grow need to be harvested in a cycle that has a similar time scale!

All stone, sand, aggregates, and clay are renewable, but on a geologic (extremely long) time scale.


One of the most important features of an ecological building material is that there should be abundant supplies of it. We can, of course, have an influence over which living resources are abundant enough for us to harvest: we already manage many species of softwood and , increasingly, hardwood trees by planting them on a sustainable basis. Also gaining favor is the idea of mixing species within a plantation to provide a healthier, more diverse environment, thus producing greater abundance (see the LIVING RESOURCES section).

Of our mineral resources, there are some that are rare and some that are abundant. Stone in many of its forms is the obvious example of a very abundant natural material. The problem is how to extract stone in a way that is least damaging to the environment. Problems occur when the wrong site for extraction is chosen—a national park, for instance—and when the volume of stone removed by the extracting company is out of proportion to the scale of the landscape.


All materials require processing or shaping to some extent before they can be used. Those that are synthetic or require very heavy processing are much less likely to be ecologically sound. Though this is not a hard and fast rule, it should make us think twice before accepting a processed material when an unprocessed one might be more appropriate.

Examples of highly processed materials are most of the metals, all plastics, and , to a slightly lesser extent, cement and glass. The last example, glass, is a material that has so many other positive ecological attributes (it is energy-saving, healthy, transparent to light, strong, durable, nonpolluting, recyclable, abundant, etc.) that its high processing costs are balanced by its considerable advantages.

There are also an enormous number of synthetic organic compounds that do not occur in nature. Many of these are hazardous to our health to a greater or lesser extent. Some, of course, have been expressly developed to be destructive to life, such as insecticides. The main reason that they pose such a threat is that they are produced industrially on a massive scale. The use of the word “organic” here is almost perverse, as it merely means a substance containing carbon, rather than its commonly understood meaning of being derived from living organisms. However, most organic chemicals are derived from the processing of oil or coal, which have them selves been derived from living matter (see the PROCESSED and SYNTHETIC MATERIALS section for further information).


Recycling is one of the fundamental principles of ecology. Every item of waste is a potential input to another use or process. If a by-product is produced which can't be used, is toxic, or is difficult to reprocess, it is questionable whether the by-product should have been produced in the first place. We need to think of all the resources we use as part of much more sophisticated and interdependent cyclical systems.

Waste is a relatively new phenomenon, one that, unfortunately, most of us living in Western societies accept as quite normal; yet, until two centuries ago, there was virtually no waste, and what waste there was, was biodegradable. At the present time, the quantities of waste that our society produces are truly staggering. The building industry provides a terrible example. We have the idea that we can throw something away, but we are learning to our cost that the garbage can is our very own earth (see the RECYCLING section).


Energy costs can sometimes represent a very high proportion of the total cost of materials. Around 10% of all British industry’s energy requirement (or 5% of the total British energy consumption) is used to produce and manufacture building materials and products. This energy is now referred to as “embodied” energy. Most of the materials that embody this energy are used in the renovation and extension of existing buildings, because the annual rate of new building is only a very small proportion of the total existing stock. In the housing sector, the annual new-build rate is at present no more than 1% of the total housing stock.

In any particular house renovation most of the materials, and thus the embodied energy, are already in place. However, given that domestic improvement cycles are as frequent as every 10 to 15 years, the embodied energy value of improvements can compare with the energy used in occupying the houses. In the past, people did not renovate their houses so frequently; nor were kitchens, bedrooms, and bathrooms constantly being refitted.

Life-Cycle Energy Costs

What are the different ways in which energy is consumed in the life of a particular building material, whether as a part of new construction or renovation work?

Energy is typically used in each of the following stages of a given material’s life cycle:

• extraction

• any processing or manufacture

• transportation

• installation

• maintenance

• demolition or recycling

The most relevant and enlightening comparisons can be made in the energy costs of production: the energy consumed in felling, sawing, and trans porting timber has been estimated at 580 watts per ton. Taking this as a baseline figure, the energy costs for some other materials can be approximately measured and compared as follows:

Aluminum: 126 times the average energy required for timber processing:

Steel: 24 times

Glass: 14 times

Plastic: 6 times

Cement: 5 times

Bricks: 4 times

Of course, these figures need to be interpreted in terms of the amount of the material required to fulfill a particular function. Also, it is important to note that 90% of the energy needed to make wood comes from the sun, whereas all the energy needed to make a fired brick comes from fossil fuels.


There are a number of reasons why locally obtained materials are a good ecological choice. The cost of transport is an obvious consideration; however, the use of the local vernacular building materials is perhaps the most interesting point.

In the past, vernacular construction methods and styles developed from the use of local materials that were readily available. The oldest vernacular building construction used wood and mud, and , later, thatch for roofing. Gradually the materials that were found to be most durable and efficient were used preferentially, and styles that were appropriate for the local climate were developed.

Over time, regions developed styles of building and crafts that were harmonious and appropriate to particular localities. It was only with the coming of extended transport systems that house-building materials from other regions became available. Fashions and ideas imported from abroad then began to take precedence over traditional local practices. Sometimes this led to an improvement in the vernacular style, but it could equally well lead to particular images that people wanted to emulate. Vernacular styles were then looked down upon as not being fashionable, or else they were associated with the oldest and often poorest housing. National standards often destroyed local styles and traditions. Developers had little thought of keeping to the vernacular. Finally, the increased movement of large populations led to the loss of an awareness of distinct local styles.

In other words, if the green philosophy of building for durability is to be generally adopted, it is likely to result in much greater interest in localized vernacular design at every level, from the general approach to scale and orientation to details of external joinery, roofing, and walling materials and actual methods of construction.

We must develop a local vernacular again. This will give each locality a unique style, which is exactly what we like about scenic and historic regions (in Britain, these include places like the Cotswold or Dales villages). There is a lot to be said for each area once again developing its own building materials and styles, rediscovering its own unique character, and providing employment for skilled local craftspeople.

‘When renovating your house, if it is an old one, it is useful to identify the original features and materials that were used and to consider which of them could be reinstated. It is also important to be able to distinguish between mock vernacular (often simply a phony facade superimposed on undistinguished construction) and good local practice.


There are different types of durability, which include:

• Strength or non-breakability

• Non-flammability

• Ability to withstand water or high humidity

• Ability to withstand attack by pests or fungus

• Ability to withstand exposure to light and UV radiation

• Ability to withstand attack by chemicals

• Endurance against mechanical or electrical breakdown

Vernacular use of materials

It is important that we use only those materials which are appropriately durable: for instance, a polyethylene bag floating in the sea is inappropriately durable, as are washing detergents that are not easily biodegradable. When it comes to components of our houses, we need the basic structure to be as durable as possible, whereas those parts we want to change from time to time, like the wallpaper and certain paint surfaces, need to be biodegradable at the right time. Worthwhile things like a well-crafted chair or table should be durable and , perhaps even more importantly, so should our windows and doors. If we look at successful structures that have with stood the test of time, we are often given a clue as to which materials and designs can help us to achieve this worthy goal, which leads us into the discussion of design efficiency.


Although this is not strictly a characteristic or quality of a particular building material, it is of such importance that it needs to be addressed. What might some of the criteria of design efficiency be? The following are eight considerations to he taken into account, in addition to the ones above, when making a choice of materials:

Minimum use of materials: producing small and light components where appropriate, and miniaturization in some cases.

• Simplification of design, to fulfill its basic function.

• Safe design for fire. Besides being life-threatening, fire is an indiscriminate destroyer of household resources.

• Multifunctional design, leading to versatile products.

• Design from natural forms. If we look carefully at what has succeeded in nature, we see just how well adapted and well designed living structures really are.

• Design to shed water and prevent damp and decay.

• Design to prevent insect attack and its resulting damage.

• Design for solar efficiency, to maximize the use of the sun’s energy.

Good design is an integral part of using ecological building materials to their highest efficiency. Now it is up to us to have some fun finding ways to achieve this!

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