What makes a material “sustainable”? There are multiple aspects to consider when rating a building material on sustainability.
The method of production, amount of energy used during production and transportation, availability of raw material resources, recycling potential, and the amount of pollution released in production, usage and demolition of each sustainable building material all contribute to an overall sustainability footprint.
Why should we care if a material is sustainable? The second highest consumption of raw materials (after the food industry), is the building industry.
This includes both renewable and nonrenewable raw materials. A nonrenewable material is one that can be gathered or harvested only once, such as crude oil or manganese, as opposed to a renewable material like timber.
Some nonrenewable materials have relatively small global reserves; copper lead, silver and a few other mineral materials have remaining reserves estimated at around 20 years or less. Others, while still classified as nonrenewable, such as potash, sodium chloride and clay, have very large reserves at the present time.
To consider the ecological impact of building materials is to acknowledge ethical and moral responsibilities to future generations inhabiting the planet, and to place value on Nature itself, the ground of out existence.
This stance is not necessarily in opposition to economical, political or societal interests, but rather an expanded viewpoint that takes into consideration the interrelationships of multiple whole systems in a long-term context.
Energy Costs and Sustainable Building Materials
Even before any operational energy efficiency of a building comes into play, there can be considerable energy savings realized from paying attention to the energy consumption of it’s materials. One often overlooked energy cost of material is the energy expended in transporting it from it’s raw extraction or harvest site to it’s production site, then to secondary manufacturing and distribution sites and finally to the construction site.
Air transport is by far the most energy intensive of all methods of transport, using up to thirty times the overall energy of the competing modes of transport, such as truck, rail or sea transport.
The most energy efficient transport mode at the present is by electric engine-driven rail, therefore, use of materials from overseas should be kept to a minimum, particularly for heavy materials such as concrete and steel. The ultimate in sustainability in terms of energy consumption is to use locally gathered recycled materials whenever possible.
Another form of energy cost of materials relates to the energy consumed at the building site. Choice of material can have a big impact here, both during construction and when doing maintenance and repair on the building.
Modern concrete construction methods, for example, call for usage of large industrial fans to accelerate drying times. Use of brick in place of concrete, where possible, eliminates this energy cost.
Total consumption of energy used is highest for the following materials. The list is shown in order from highest energy consumption, to lowest, including all steps from extraction of raw material to finished product:
Polyvinyl Chloride (PVC)
Flax Fiber Matting
Laminated Cardboard Sheet
Kiln Dried Timber
Reinforced Cement Slab
Calcium Silicate Sheet
Reinforced Structural Concrete
Lime Mortar and Plaster
Sustainable Building Materials and Pollution
Energy expended in the extraction and production of building materials not only depletes nonrenewable resources, but it creates pollution as a byproduct. Fossil fuel combustion causes the most pollution, of course, emitting substances such as carbon dioxide, sulphur dioxide, nitrogen oxides, and particulates that contribute to global warming.
It is estimated by the U.N. that 30-40% of greenhouse gas emissions worldwide are due to the construction industry. Nuclear power also poses problems to the environment, including risk of radioactive leaks and waste disposal.
Transport of materials to refining, production and building sites also is a source of pollution, depending on mode of transport. Air transport produces by far the most pollutants per mile traveled per given unit of weight, followed by light diesel truck, with large container ship and railway being the least polluting.
Building materials also contribute to pollution directly, during the construction, the usable life of the building, reconfiguring and remodeling, and eventual demolition. The majority of the pollution occurs during the construction phase; while off-gassing, dust, decay, and radiation emission can pose a health hazard to inhabitants, the risks are relatively small.
Construction waste and scrap from demolition activities constitute a major pollutant source, as leech from landfill and emissions from incineration. The amount of hazardous material contained in construction waste is small, but considering the fact that there are over 80,000 different chemicals in use in the construction industry today, the effects on the environment are often overlooked.
Of particular concern are materials containing heavy metals, and non-biodegradable plastics.
Global warming potential is highest for the following materials. The list is shown in order from highest greenhouse gas emission, to lowest, including all steps from extraction of raw material to finished product:
Kiln Dried Lumber
Reinforced Concrete Slab
Lime Plaster and Mortars
It should be noted that timber can be considered to be carbon neutral in many cases, due to it’s carbon capture and storage capacity. Buildings constructed from timber and other vegetable materials such as hay bale, store carbon as long as they are standing.
This is because during growth, plants absorb and bind from the atmosphere large amounts of carbon dioxide, through photosynthesis, and this carbon stays captured after the plant has been harvested, not being released until the material is either incinerated or decays. A typical 120 square meter house built from timber can store about 32 tons of carbon dioxide.
Top Photo by Martin Pettitt