3 BUILDING MATERIALS: AN ISSUE FOR ANALYSIS

Selection and use of materials for construction has always been a core concern of architecture and building science. In contrast, widespread concern about environmental impact has been an issue only for a few decades. Initially, during the years when 'Limits to Growth' was a catch-phrase for the embryonic environmental movement, emphasis centred on resource depletion. Nowadays, debate revolves more around environmental consequences of extraction and manufacture, and around recycling and final disposal. As with fossil fuels, straightforward resource depletion has faded from prominence in the light of realistic projections for supply well into the next century.

Similarly, recycling of building materials has a long history but has only recently become a topic for environmental analysis. For most materials, embedded energy (essentially the energy used in manufacture) may be almost irrelevant although it is one reason why recycling of glass containers is undertaken on such a large scale. Life cycle analysis may be applied to highlight the key concerns for any material, subject to acknowledgement that conclusions may vary from region to region.

The problems of agreeing the environmental merit of various materials are well illustrated by the debate over wood. Arguments can be advanced for and against its use. Incorporation of timber into a building can 'lock up' atmospheric carbon for a number of years, thus perhaps delaying global warming, but use of a renewable resource must not be claimed as environmentally friendly if its extraction causes ecological harm in the producer country. Friends of the Earth have argued that alternatives to tropical hardwoods should be used in buildings (40).

Also in the UK, an industry grouping, Forests Forever, has been set up "to help safeguard the forests of the world by encouraging improved forest management, responsible trading and promoting the positive environmental aspects of using timber" (41). Booklets from the Timber Trade Federation contain publicity hype "Every time you don't specify timber, you're helping to destroy our planet", as if all use of timber was commendable. The same brochure (42) lays great emphasis on the energy needed to manufacture timber buildings being less than for competing materials such as steel and aluminium, despite that the major commitment to use of energy will usually be for building services.

No material can be claimed to be environmentally the best in all circumstances. For example, timber may need toxic chemical treatment to ensure a reasonable life, whereas uPVC window frames may be benign until disposed of in an incinerator - when highly toxic chemicals may be formed. Materials may be assessed more on their intrinsic qualities than on their contribution to design. Thus for glass, one of the most ubiquitous of modern building materials, the assessment locally may be similar in all areas but the use of glass may yield great benefits or disbenefits in a particular building.

However, exhortations such as are included in BREEAM to ask timber merchants whether their stocks are from sustainedly managed sources are of little use when there is no way that most or any of them could answer the question with certainty. Recent investigations by Friends of the Earth (FoE) have confirmed both that wood sold as coming from sustainable sources was incorrectly labelled and that companies involved in 'illegal' trading have claimed to have adopted environmentally friendly policies. One was recently awarded the FoE Green Con award (43). More recent publicity has again claimed that the trade in tropical hardwoods such as mahogany is out of control. A temporary ban on all trade has been advocated (44).

Complications arise because some materials that have traditionally been used in buildings, without any protest from environmentalists, may soon become in short supply or the subject of local anguish as new reserves are considered for exploitation. Aggregates used in concrete are one example. Although individual building materials are candidates for cradle to grave environmental assessments a recent scheme for undertaking these produced no response from the UK building industry (45).

Despite there being no substantial basis of agreement on what is an environmentally friendly or unfriendly material, and little prospect of many agreed cradle to grave assessments, significant progress has been reported from Sweden in life cycle analysis of materials and products in industry (46). For building products, the issue may be more complex because each source of supply of many materials might need an individual assessment, complicating the assessment of buildings by requiring that each supplier be required to produce the requisite evidence. This could rapidly lead to unworkable bureaucracy and to the original objective, of limiting primary environmental damage, being lost amongst the paper-work.

Progress on building materials assessment must take account of:-

• the sustainability of the basic resource

• the damage consequent upon extraction of raw materials, both temporarily and in the longer term

• the energy used in transport and manufacture

• toxic chemicals released to the environment anywhere from extraction to final disposal (cradle to grave)

The difficulties of assessment may be highlighted by considering asbestos and wood. These are at opposite ends of many peoples ideas of healthy or friendly materials.

Asbestos has now been largely phased out of buildings components, despite the very low risks in normal use of many composite materials (47). Use of asbestos cement products in developing countries may however still be a viable and sensible option, as they may be cheaper than alternatives and enable the construction of much needed buildings.

Wood from tropical forests may, at the present time, be assumed to have come from sources that are not managed sustainedly and its use may be assessed as environmentally damaging. This would be especially the case were the wood to be used for internal decorative purposes or for on-site shuttering, uses that might be considered environmentally insensitive.

Labelling of timber is a distinct and global problem. Only when a credible scheme is in place can it be incorporated into an overall assessment methodology. In the interim, avoidance of all timber from countries known to be damaging mature forests in tropical areas may serve to focus attention on the primary environmental issue of habitat and biodiversity, despite that the timber industry is not the primary cause of deforestation. In principle however, wood can be one of the most ecological of materials, a fact noted by the Timber Research and Development Association (TRADA) in an early defence of the industry. (48)

In view of the unproductive complexity that could result from attempts to assess the detailed environmental credentials of materials, it may be advisable to focus attention upon primary environmental damage and upon severe local (usually secondary) consequences. There are many other genuine factors that will determine use of a given material in a building including durability, security, appearance, cost, and structural strength, and the most that may be hoped for in the near term is to avoid use of materials associated with primary environmental destruction.

Probably a major impact will be increased recycling and reuse of materials, as an alternative to primary production. Much could be accomplished at present were economics to shift in favour of paying for labour to sort and recycle materials, and not only in the building industry. Interestingly, it may be the high cost of disposing of used materials and unwanted by-products in environmentally acceptable ways that forces appraisal of the recycling option. This would parallel developments in the car industry notably in Sweden and Germany where ease of recycling has already influenced component design. Adjusting market conditions to encourage thought about the long term consequences of constructing buildings in a particular way and with particular materials is a strategy with which few would argue.

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