Specifying materials for resource efficiency
Tanisha Raffiuddin of the Passivhaus Trust reports on the ASBP’s Future Footprints seminar
The Alliance for Sustainable Building Products (ASBP) recently held an event entitled Future Footprints: Building Products in a Resource Efficient World. Resource efficient construction means making best use of materials, water and energy over the whole lifecycle of built assets to minimise both embodied and operational carbon. The event looked at the environmental impacts of various materials used in construction and what factors designers should consider when specifying.
The construction industry accounts for approximately 55 per cent of the total annual materials consumption and 50 per cent of total CO2e. It is also responsible for 30 per cent of total UK water use and 35 per cent of arising waste. If the UK is to meet its carbon emission targets by 2050, these figures have to be slashed by 50 per cent.
According to Cambridge University professor Julian Allwood, keynote speaker and author of the informative book Sustainable Materials with Both Eyes Open (2011), the UK has not made much progress in reducing emissions. In fact, emissions have risen by 20 per cent since 1990.
The breakdown of global industrial carbon emssions shows that 55 % is used to make five stock materials - steel (25%), cement (19%), paper (4%), plastic and aluminium (3%). Around half of all steel is used in buildings, similarly with aluminium, but ALL concrete is used in buildings and infrastructure. It will not be easy to cut emissions related to steel and aluminium as their demand is estimated to double by 2050. The challenge is not simply halving emissions, but halving emissions while demand doubles.
Material efficiency strategies
Allwood argues that even if we do everything we can to reduce emissions globally (cut down energy needed for manufacturing, decarbonise the grid, recycle materials and so on), by 2050 we would still be at the current levels of emissions. We need to address the challenge ‘with both eyes open’ and change the flow of materials through the world economy.
Allwood proposes six material efficiency strategies:
- Reduce yield losses
At the moment, one quarter of steel that is manufactured gets converted into scrap.
- Divert scrap
Divert scrap metal for another use rather than melting it.
Reuse metal rather than recycling it.
- Use less
Approximately one third of material can be saved by more efficient design. This is usually not done as labour is more expensive than materials, and solutions are chosen to minimise labour costs.
- Keep goods for longer
Given that the stock of steel is fixed, the longer we keep the metal, the lower the rate of production each year will be to replace them.
- Reduce demand
If these material efficiency strategies aren’t enough, then consider reducing demand.
John Dowling from the British Constructional Steelwork Association (BCSA) pointed out that currently only 13 % of steel is reused while 91 % is recycled. There is nothing overly technical about re-using steel, and the supply chain has been in place for many years but buildings must be designed for disassembly. In the case of Prologis Park at Heathrow, 80 per cent of the steel was reusable after the structure was dismantled. Another example is the BCSA HQ in Yorkshire which utilised 82 tonnes of reconditioned steel already existing on the site.
A drive to re-use more steel will lead to less composite construction, changes in the demolition process and wider adoption of bolted over welded assemblies.
Timber is widely promoted as a sustainable material because it is renewable. Carol Costello of Cullinan Studio presented an overview of the practice’s timber buildings from gridshell structures to glulam and cross- laminated panel projects and standardised systems for schools. Costello pointed out that resource efficiency is also about designing buildings that look good so that they are appreciated and looked after by their occupants and will last longer.
Embodied carbon calculation methods
Sean Lockie of Faithful & Gould reviewed the RICS guidance note, ‘Methodology to calculate embodied carbon of materials.’ The guidance note currently addresses the product stage of construction: raw materials supply, transport, and manufacturing. It will be broadened to include construction up to end of life stage. Lockie highlighted the challenges of embodied carbon footprinting because most contractors have no experience with embodied carbon budgets. Other factors include carbon factor validation issues, weight and quantity of materials, and maintenance and replacement of materials.
Lockie discussed examples of good practice of whole life carbon measurement through four case studies, including the London 2012 Olympic Games. One of the core strategies was the use standard design codes across the park. Key outcomes were the use of low carbon concrete mixes (PFA and GGBS), local sourcing and less materials.
A variety of construction product level data can be used to make whole life cycle design choices (e.g. LCI- Life Cycle Inventory, LCIA- Life Cycle Impact Assessment). Jane Anderson from PE International stressed that to make the appropriate material choices, it is important to identify which life cycle stages and elements of your building will have most impact and focus on them first. A good place to review product information is either generic databases or manufacturer specific Environmental Product Declarations (EPDs) and Ecolabels.
Each step of the supply chain offers opportunities to improve resource efficiency. Clients should set requirements for good practice and measurement, while contractors should implement good practice and measure performance. Collectors and processors should recover more waste and provide robust data.
WRAP’s Gareth Brown highlighted several relevant WRAP initiatives including a Low Carbon Route-map for the Built Environment, Resource Efficiency Action Plans (REAPs) and an Embodied Carbon Benchmarking Database (with UK-GBC).
What can designers do?
The three most important factors for judging a material’s sustainability are recyclability, overall environmental impact and embodied energy/ initial carbon footprint. Designers must identify and focus on the most impactful aspects of the building and use EPDs and other LCA data to make material choices. This also means designing with less material, using materials with greater longeivity, reducing waste and increasing recycling.
Another question to ponder - can we design products so that we can either modify them as our needs change, or upgrade them as the market offers new components?
The value of a building can also be maximised by considering flexibility and adaptability in design. Dowling notes that the Dutch version of BREEAM recognises the importance of measuring flexibility and adaptability Estimated Service Life (ESL). BIM has enormous potential for increasing resource efficiency across the entire design, construction, operational and end of life stage.
As the most significant consumer of the earth’s natural resources, the construction sector will need to get ‘more from less’ if it is to respond to the increasing pressures of cost and environmental impact. To meet this challenge, the ASBP advocates a move away from commoditised, generic materials, towards a value-added model, which rewards product innovation and intelligent design. This will lead to greater resource efficiency, as well as better building performance. To paraphrase Gary Newman, director of the ASBP, if we don’t make the right choices, ‘we will go down in history as the only species that measured our own extinction.’