sustinable use of materials

Defining what materials are, or are not, sustainable is the single most difficult thing to do when designing an environmentally responsible landscape (or any construction). All materials have an ecological price tag, and it is often hard to judge one thing better than another.

A classic example of this is paving: is it better to use locally produced concrete paving, which is readily available, or to use (say) Indian sandstone, which has a lower energy input in its production but high transportation costs and possibly utilises child labour? Both have a similar financial costs, but different environmental ones. Until someone finds a way to do accurate audits of these issues, there are no clear answers.

Some things are more obvious, however, such as tropical timbers. When choosing timber it is always best to specify FSC (Forest Stewardship Council) timber, which is certified with a “chain of supply”, which means you can trace each log's origins. However, all tropical timber is still suspect as little can be grown in plantations (apart from some Teak). The only time I will use any tropical timber is if it is reclaimed. Also, timber from your local sawmill may not be FSC certified but it will be local and either native (such as oak) or plantation grown. Keeping transport down and supporting local business is also important, although your local sawmill may not have much environmental awareness.

Specifying less damaging materials may be inconvenient and sometimes more expensive but we have to remember that the financial cost is not the real, or the main cost. Also, the more such things are specified, the easier it becomes to obtain them, as suppliers react to demand.

The other inhibitor to using less conventional materials is that contractors may not be familiar with construction methods and the long-term performance may be unknown or at least uncertain. However, good research and communication is the main method of overcoming these issues. We have to be prepared to step beyond the boundaries of our knowledge and experience, in order to gain new benefits.

Selection is often a balance between new materials and methods and more traditional ones, such as use of lime mortars, cob or rammed earth. Such traditional materials have a low impact and energy input (lime still requires kiln firing but to a far lesser extent than cement). Often the old and the new will mix directly, such as the use of “hempcrete” in wall construction. Hemp is grown and harvested, dried and shredded, mixed with lime mortar and blown into shuttering and allowed to set. Hemp is a fast growing crop which gives high yields per hectare, as does bamboo, which is increasingly seen as an eco-building material. However, the high transport costs make it unviable (ecologically) in temperate climate areas.

The market for sustainable materials has hardly begun to be recognised but it is certain that this will expand considerably over the coming years, especially as transportation costs continue to rise. Keeping abreast of new developments in this field is therefore vital.