Most modern designs consider energy as the most important factor in the sustainability of buildings; however, it is not only the energy a building consumes that impacts on its overall sustainability. Materials form a very important factor when analyzing their embodied energy, reusability, recyclability, and impact on both their occupants and the environment as a whole. Materials require to be carefully selected, taking into account their whole life cycle, including their raw material composition, energy mix, production location, durability, long term effects and end use.
Table of Contents
The following paper is divided into two main parts.
The first section Material Background explores all aspects of materials, including what the life cycle stages are and what implications each life cycle stage has in terms of environmental sustainability. It provides the necessary overview to enable an educated selection of materials.
The second section Material Selection Process is dedicated to the material selection stage itself. It gives guidance on the process of material selection in order to create initially a material shortlist and subsequently make an informed decision.
A sustainable building can be viewed as consisting of a number of sequential stages:
- Design stage:
The design and specification of the building as a system (location, shape, size, systems, function)
- Construction stage:
The materials that the building will consist of (superstructure, structure, finishes, furniture)
- In- service or occupation stage:
Servicing and making sure the building is working as designed (lighting, filters, maintenance, service)
- End-of-life stage:
Disassemble, demolish, recycling, disposal of components and materials.
All materials used in the building have their own life cycle, some last as long as the building itself, while others are subject to constant renewal or exchange and replacement.
The design stage of a building is the most important stage, defining the constraints in which the building and its occupants will operate. The actual design and layout of the building influences the use of resources such as energy, water and air, during the buildings lifetime and its consequential overall impact on the environment.
In addition, the materials used in and to form the building have a significant impact on the environment. Consequently, when selecting materials for a building, the whole life cycle of a material requires consideration.
This can be a challenging journey for the ordinary specifier who generally is not a scientist and does not have access to a Life Cycle Assessment (LCAii) or LCA comparison of all the options.
Many materials selected especially for interior fit outs have a significant shorter lifetimes than the building itself.
The lower the durability of a material is, the higher the impact of manufacture, installation and disposal will be. The higher the durability is, the higher the maintenance impact is.
Materials themselves feature similar life-cycle stages as the building itself.
- Product design
- Raw material acquisition
Each of these stages has an impact on the environment and uses other resources. They require input, processing and cause output. Often, significant transport is involved as well.
Most products today are designed for a useful service life. Usually no consideration is taken for the end of life stage. Clever product design involves not only creating a good product but also making a product which can be reused or recycled or degrades easily and fast. At the end of its life, the product should go back into a biosphereiii or technosphereiv loop to provide either nutrients for nature or feedstock for a new product of at least equal quality.
Raw Material Acquisition
The raw material acquisition for material production can be energy intense, cause pollution and leave toxic by-products.
The impact of raw material acquisition is included in the embodied energy of materials and products and is also included in the cradle-to-gatev LCA calculations.
The material production phase involves various raw materials and production processes plus transportation.
Production can contribute to water and air pollution, uses energy in various forms and produces the desired product plus by-products and waste.
This phase is included in the embodied energy and LCA cradle-to-gate calculations as well. Embodied energy data usually includes the energy to actually produce the product, but not to process any by-products, waste and contaminants.
Cradle-to-gate LCA accounts only up to this stage, as well as most green certification schemes. Some embodied energy calculations stop at this stage and do not take into account any in-service stage or disposal scenario, some do.
It is therefore imperative to check the boundaries of any certification or embodied energy calculations.
Once produced, the product will have to be loaded, transported to the building site, unloaded and added to the construction.
Tools are required to unload and install the product. If not produced to size, leftovers will have to be dealt with. These leftovers are directly entering the end-of-use phase and end up in reuse, recycling, downcyclingvi, landfill or incineration.
Some products will need maintenance during their lifetime, like cleaning or painting. These processes will require further resources and processes, having in turn their own LCA assessment requirements and impacts.
Some materials will need maintenance in order to achieve a certain level of durability.
Materials have to be easily disassembled in order to be reused or recycled.
Most composite materials are not good for anything but landfill.
Reinforced concrete is an example where the two components – concrete and steel – can be easily separated and recycled separately. The steel can be put back into the steel production loop and the concrete can be downcycled to gravel or as filler in new concrete.
Aluminium windows can be disassembled, with both the glass and aluminium recycled and turned into new products.
Some materials can be reused a number of times. Bricks are a classical example. Bricks have to be cleaned from mortar – this is part of the disassemble process – and can then be reused almost indefinitely. At least that used to be the case before the use of cementious mortar, which forms a strong bond and cannot be easily removed without damaging the bricks.
There are many other examples like timber floor boards, bathtubs, taps, tiles, doors, windows and many more. Buyer demolition yards are big overseas, an example in NZ is Ward Demolition who strip buildings, separate out the waste and resell the viable items for reuse.
Some materials can be almost indefinitely recycled like aluminium and PET. Some other materials can only be recycled a limited number of times, for example paper.
Post consumer PET can be recycled into thermal and acoustic insulation products, unfortunately, it usually cannot be used for food grade applications any more, unless depolymerised as it loses quality and purity.
Aluminium recycling is still a very energy intense process although less intense than the production of virgin material. Recycling aluminium uses approximately 20% of the initial production energy. About 51% of aluminium is currently recovered in NZ for recyclingvii. Consequently, by using an aluminium product, 49% of the aluminium will be virgin material at this stage. The total energy used for the manufacture of aluminium products in NZ is reduced to approximately 60% of new aluminium, which is still very high.
Downcycling describes a process of recycling a material into a material of lesser quality. Examples comprise the combination of plastic components and sawdust into park benches or PET bottles into a composite timber product.
As soon as a pure material is mixed with another substance, a so called composite or hybrid material is formed, which, cannot be separated back into its original components. It can no longer be recycled and will eventually end up in landfill.
Products that cannot be used in any process any further have to be buried in landfill or incinerated. Certain materials like some metals or plastics will last virtually forever in the ground, it is therefore important to recycle as many of these materials as we possibly can. This is particularly true for metals like copper and aluminium which can be easily recycled and have a high embodied energy. It is also true for heavy metals which can potentially contaminate the environment. Plastics should be recycled because of their durability, their petrochemical base and ease of recyclability.
One particular problem in New Zealand is the use of treated timber at levels higher than H3.1. This cannot be reused, recycled, composted or domestically incinerated. It can only be incinerated in controlled thermal power plants with appropriate emission filters or be buried in landfills, where the chemicals, mostly arsenic, chromium and copper, will remain toxic for the long term and cause risks for both the environment and future generations.
Burying resources is our last resort and worst case scenario.
Material selection process
Understanding the Material Life Cycle
As outlined before, a material has three main life cycle stages: Production, Use and Disposal. The design stage effectively influences all of these stages.
Cradle-to-Gate assessments including eco labels do not necessarily give a good indication of whether a product is sustainable, because the product will eventually end up in landfill, unless it is designed to be reused or recycled.
The use of a material in addition to the disposal of a material will affect sustainability. Depending on the type of material, significant impact can occur in both stages. Imagine a cladding that has to be painted repeatedly or your shower that needs cleaning regularly.
Below is a comparison of aluminium weatherboard, cedar weatherboard and vinyl weatherboard.
The following tables are taken from the LCA tool BEES 4.0viii.
The results are for a functional unit of 1 ft2 0.09 m2 for a period of 50 years.
The first chart shows the material rating without transport, whereas the second chart shows 8000km added for transport for the cedar cladding.
In terms of overall rating, the aluminium cladding performs slightly better than the cedar cladding, even without any transport implications added to it. If transport is added to the cedar, bearing in mind that it is imported from Canada, its actual environmental benefits diminish significantly.
In terms of fossil fuel depletion and global warming potential (GWPix), the cedar performs better as long as no transport component is added, otherwise the vinyl performs better in terms of GWP.
Some experts are of the opinion that our foremost target is to reduce the GWP, in this respect the vinyl would be a good choice, however, when viewed in overall terms, it is obviously not.
Green Roofs are known to extend the durability of the membrane, reduce peak storm water runoff, provide higher insulation levels, significantly raise biodiversity and have a positive social impact. On the other hand they require more structure, more layers with additional material and transportation input and higher design requirements. Consequently, they have higher construction costs and impact more on the environment.
To summarize, there are environmental advantages and disadvantages to all materials and obvious economic disadvantages that go hand in hand with social advantages.
There are many questions and considerations that impact on our decisions. Life cycle Assessments that have been done in the past show, that green roofs can be sustainable not only in respect of environmental aspects, but also in economic termsx.
Floor coverings are another good example. A usual perception is that linoleum is a good sustainable flooring material; the same perception applies to woolen carpets.
The following tables are taken from the LCA tool BEES 4.0.
The results are for a functional unit of 1 ft2 0.09 m2 for a period of 50 years.
The graph clearly shows that linoleum would be the best choice, even though it will need more care and cleaning during its lifetime, followed by vinyl, nylon and then only wool carpet. All floor coverings are calculated for a period of 50 years with the necessary cleaning, replacement and landfill disposal.
Please be aware that this is valid for generic North American products. The New Zealand market and products are different from the American ones. Also individual products can vary significantly.
The result shows clearly that the preferred products would be linoleum or vinyl, depending on the question whether a more economic or ecological approach is taken. If we take a look at the economic side of things, the vinyl might seem to be the preferred option. However, this view does not take into account the potential impact of chlorine production or plasticiser offgasing during the products lifetime together with potential human health implications associated with itxi.
This is an interesting result and shows we cannot readily trust our perception.
Vinyl and nylon in comparison with wool shows that sustainability is not necessarily a question of whether a product is natural or artificial, it is rather determined by the substances required in the process of manufacture, the use cycle and the disposal scenario.
Life Cycle Assessment
Life Cycle Assessment is a good way to determine the suitability of a product. Unfortunately there is no LCA data readily available for all materials. There might be some overseas data available, but in virtually all cases not for the New Zealand market. LCA results from overseas cannot simply be transferred to New Zealand. Sometimes production techniques vary significantly, the material composition is different and the energy mix in New Zealand is different from other countries. These factors all influence the LCA result.
What can we do when LCA data is not available? We have to trust our knowledge and gather as much information about the products we use.
Ranking of Products
When selecting a certain material or product, we should be aware of the implications of our decision. By specifying the wrong product, we could be actively contributing to pollution, global warming, climate change or human health issues.
Consideration is needed as to what the short term and long term effects of the selection will be in terms of sustainability.
Black List: Avoidance of hazardous ingredients
As a first step, the material selection process should avoid materials containing or emitting known or potentially hazardous substances, such as those that are teratogenicxii, mutagenic, carcinogenic or otherwise harmful for humans or the environment.
This should also include substances that are strongly suspected of having a negative impact, even if this is not absolutely proven.
This avoidance list should obviously include materials containing substances like asbestos, arsenic, chromium, benzene or similar.
PVC flooring would be a good candidate for this list as alternatives are available.
Grey List: Problematic substances with no viable replacement
There is a wide range of substances that fall within the black list but have no viable replacement at this point in time or a replacement that will suit a specific application.
This list also would contain materials that contribute to the reduction of negative effects on the environment although still being problematic. Examples would include aluminium for shade louvers, solar panels, photovoltaic panels, PVC windows and similar items.
This list should also contain products and materials that can be indefinitely recycled while containing problematic substances so long as these substances are kept in the production loop without releasing toxins, they are deemed to be relatively safe, although there is always the strong possibility that not everything will be recovered and recycled at the end of the products lifetime.
Products that are safe
This list contains materials that are non toxic, indefinitely recyclable or biodegradable. The most prominent example is untreated timber.
Products in this category should also have low embodied energy and should require little energy to recycle.
In order to create your black, grey and white list, you need to collect as much information about a product as possible. Information provided usually only covers environmental certification and the base ingredients.
In most cases, the information provided by the manufacturer is not usually sufficient to make a decision. It is recommended that the manufacturer be contacted and requested to supply any missing information. If they are serious about their product, they will provide the necessary information.
Questions and information to be requested includes a full declaration, physical properties, certification, recyclability and product stewardship for the product and environmental management system, sustainability policy, recycling and waste management policy of the manufacturer. You may find this can be a fruitful conversation.
If the information available indicates that a product contains ingredients that are potentially hazardous or to be avoided or previously determined on the black list, put the product on the black list and stop any further research here. You might consider contacting the manufacturer and informing him about your decision to give him feedback and give him the chance to enhance the product in the future.
There might be the case that despite of the composition there is no alternative available then try to ensure that this is really the case.
Instead of considering the ingredients of the recipe, it might be worthwhile reconsidering the menu, meaning you might think about your construction again, change it to find other materials and products that are more suitable for a more sustainable building.
Just in case you are absolutely sure that there is no alternative, put the product on the grey list.
If the product is a composite or hybrid that will have an effect on decomposition and cause back feeding of materials into the production loop, put it on the grey list.
Once an attempt to sort materials into lists has been made, an educated decision on embodied energy can be made. The higher the embodied energy is, the higher the GWP will be. This should be the first priority for making a decision as to whether a material is placed on the white or grey list, particularly in view of the challenges we face in respect of climate change.
Product specific data on embodied energy is usually not available for products, but there has been extensive study on the subject and a publication is available from Victoria University in Wellington, written by A. Alcornxiii.This publication gives the embodied energy for various materials and provides a good basis for estimation.
If the embodied energy is considered high, the product should go on the grey list.
If the product is biodegradable, such as those made from a natural material like timber or plant fibres, is not treated with bioincompatible substances or is a type of biodegradable technosphere product like bioplastic that degrades fast, it should be given preference over other materials because it will require no processing and no energy input to be disposed of. Good examples are local grown timbers or even imported timbers, as long as fossil fuel depletion and the GWP for transport is accounted for. Synthetic biodegradable plastics and fibres belong to the same category.
Of course there are always exceptions to the rule: If the embodied energy and the estimated energy requirements for a product to be recycled are lower than manufacturing a biodegradable product, then the first product should be given preference. This can be a hard to decision to make.
If the product is not biodegradable, it should be at least recyclable. Most products are not necessarily designed to be recycled; the process has been superimposed on them. As mentioned earlier, composites like carpet, carpet tiles, composite plastics or vinyl flooring are very hard to recycle.
Some products are only theoretically recyclable, as there is no recycling scheme available for them in New Zealand. Some manufacturers have a product stewardship which is only available in the country of origin.
Generally, plastics codedxiv 1 to 6 can be recycled, code 7 others can be any plastic not of any of the other groups, could be a mix of plastics or a proprietary one. Code numbers 1 (PET), 2 (PE-HD), 4 (PE-LD) and 5 (PP) are preferred. Code 3 (PVC) is difficult to recycle, same applies to code 6 (PS).
Insulated concrete panels can be difficult to recycle as the insulation often cannot be separated from the concrete unless specifically designed to do so. This is where the product designer can be challenged.
The option for the architect might be to use uninsulated concrete panels for the interior walls to build a high mass building and then consider using another type of structure or material for the exterior.
Once again: If you cannot source the right ingredients for your meal, think about changing the menu.
Supporting local manufacturers has many positive effects. This relates to considering the social component of sustainability by feeding money back into the local community, thereby sustaining the local economy and society.
It is also easier to establish a product stewardship, recover materials, create production networks and recycle by-products instead of creating waste.
Similarly, it is usually easier to approach local manufacturers for product and production enhancements instead of a manufacturer that might be located at the other end of the world.
Total embodied energy will be lower compared with an overseas product, even if the overseas technology is further advanced and environmentally certified.
Consequently due to the above, a local uncertified product will usually have less of an environmental impact than a similar certified overseas product. Certification can be given a lower priority.
Environmental certification is a good way of selecting building products and materials. In saying so, we should be aware of the certification framework and requirements. Various certification schemes have different specifications, consequently, not only does the certification of the particular product need to be examined and researched, but also which scheme they have been certified under.
A plastic wall board can gain certification under GECAxv by simply putting a sticker with the type of plastic onto the product and containing either 50% recycled plastic or plastic not derived from petrochemical sources. You can research the requirements on the GECA websitexvi. The product itself could be made from some proprietary plastic and the recyclable plastic sticker indicates type 7, which is OTHER and is in fact not even recyclable, but downcyclable in most other countries.
This scheme will result in environmentally friendlier products, but the question remains whether it is environmentally friendly from a total perspective.
Generally speaking, environmental certification highlights products that have less impact on the environment, but does not necessarily constitute environmentally friendly products. You might consider using a complete different product category instead or a plastic board that is made from a more common and pure plastic like PE, PP or PET that can be recycled indefinitely even if not specifically environmentally certified. In saying so, you might experience more difficulties in achieving a NZGBCxvii credit for it.
As outlined previously, certification usually covers only the cradle to gate stage, so it does not allow for transportation to site, or maintenance and disposal. Some schemes cover product stewardships and therefore ensure that some form recycling or take back occurs. Once again, read the specification to find out what will happen with the product after return, whether recycled, downcycled or disposed of.
Production and Disposal
Not only ingredients but also the way materials are produced will influence their overall environmental impact. It is important to consider whether the manufacturer uses hazardous agents in production that might leak into the water, soil or air, in addition to what type of energy they are using and whether they are providing a product stewardship programme to recycle their own products at a later stage or recycling other materials and turning them into new products without leaving unusable waste.
Most modern products will end up being unusable at some stage. Even carpet tiles that are taken back, cleaned and refurbished to be reused one more time will end up in landfill. Environmental choice certified ceiling tiles imported from the United States will eventually end up in landfill. It is most important to consider products that are not composites and can be recycled indefinitely. Composites cannot be disassembled and cannot be recycled. Consider products that can be disassembled by mechanical or chemical means; Downcycling is not an option as again the product will eventually end up in landfill.
Unfortunately there appears to be no straight forward way of selecting the right material. The selection process is difficult and needs to take into account the varied aspects of design, production, disposal and other alternatives including whether a completely different type of construction would be a better option.
There can be many loops and steps back during the material selection process. Many people have asked me in the past to create a list of recommended materials. Unfortunately, there can be no recommended definitive list because material suitability is closely connected with the type of construction and the way it is used. There may be better alternatives, or sometimes the type of construction has to be rethought and changed.
Material selection is an integral part of the design process and cannot be separated from it.
iSustainable: [to meet] the needs of the present without compromising the ability of future generations to meet their own needs. as defined in United Nations General Assembly (1987) Report of the World Commission on Environment and Development: Our Common Future. Transmitted to the General Assembly as an Annex to document A/42/427 – Development and International Co-operation: Environment, retrieved on: 15 February 2009 from http://www.un-documents.net/wced-ocf.htm,
iiLCA = Life Cycle Assessment, based on ISO 14040: LCA addresses the environmental aspects and potential impacts [&] throughout a product’s life cycle from raw material acquisition through production, use, end-of-life treatment, recycling and final disposal.
iiiBiosphere = The region on land, in the oceans, and in the atmosphere inhabited by living organisms, Environmental Yellow Pages, retrieved 6 May 2009 from http://www.enviroyellowpages.com/Resources/GlobalWarming/globalwarming_glossary.htm
ivTechnosphere = the whole of man-made materials not present in nature
vCradle-to-gate life cycle assessment defines all impacts of a material or product from all of its components and processes to produce a functional unit of the material or product.
viDowncycling is the recycling of a material into a material of lesser quality. The terms downcycle and downcycling were first used by Reiner Pilz of Pilz GmbH and Thornton Kay of Salvo Llp in 1993, along with the terms upcycle and upcycling. This term was popularized by William McDonough and Michael Braungart in their 2002 book Cradle to Cradle: Remaking the Way We Make Things.
viiFinal Report Recycling: Cost Benefit Analysis, prepared for Ministry for the Environment, April 2007 by Covec, retrieved 3 March 2009 from http://www.mfe.govt.nz/publications/waste/recycling-cost-benefit-analysis-apr07/recycling-cost-benefit-analysis-apr07.pdf
viiiBEES, Building for Environmental and Economic Sustainability, developed by the NIST (National Institute of Standards and Technology) Building and Fire Research Laboratory, http://www.bfrl.nist.gov/oae/software/bees/bees.html
ixGWP = Global Warming Potential which is the ratio of the radiative absorption per unit mass of this gas, relative to an equal unit mass of CO 2 , integrated over a 100 year period.
xComparative life cycle assessment of standard and green roofs, Saiz S, Kennedy C, Bass B, Pressnail K., Department of Civil Engineering, University of Toronto, 35 St. George Street, Toronto, Ontario, Canada M5S 1A4.
xii(adj) teratogenic (of or relating to substances or agents that can interfere with normal embryonic development), Cognitive Science Laboratory, Princeton University, retrieved 27 April 2009 from http://wordnetweb.princeton.edu/perl/webwn?s=teratogenic,
xiiiResearch and publication by the Centre for Building Performance Research, Victoria University of Wellington, Embodied Energy and CO2 Coefficients for NZ Building Materials, retrieved 2 March 2009 from http://www.victoria.ac.nz/cbpr/documents/pdfs/ee-co2_report_2003.pdf
xivMinistry for the Environment, Plastic identification codes, retrieved 8 May 2009 from http://www.reducerubbish.govt.nz/recycle/plastic-id.html
xviGECA Panel Board Standards, Version 1.1, retrieved on 25 April 2009 from http://www.geca.org.au/standards/GECA%2004-2007%20-%20Panelboard%20v1.1.pdf,
xviiNZGBC = New Zealand Green Building Council