By Jeremy Sole, Executive Officer, Sustainable Steel Council
no building product comes without environmental side effects, whether it be at the time of manufacture or at the other end of a product’s useful life.
I suspect that despite claims to the contrary, we haven’t seen any environmentally friendly building materials since the days we moved away from mud huts and thatched roofs. We have steel, concrete and timber available to us now, but each of these materials has its upsides and downsides. Given the importance of this issue, it is perhaps time for a rebalancing of some perspectives and so called ‘truths’.
I was recently at an environmental conference listening to a panel discussion where the speakers were proudly waxing lyrical about a particular groundbreaking multistorey mass timber building they had designed and built. As the panel members were espousing the virtues of this particular mass timber building, there was a timelapse video playing on the screens behind them showing the structural steel frames being raised floor by floor, and the timber elements following up behind them.
The point here is that this is a hybrid building incorporating structural steel and mass timber. When questioned on the assertion that it was a mass timber building, one of the panellists acknowledged that while the timber supports the gravity loads, it is the steel structure that braces and holds the building up against dynamic loads.
In reality, this is not a mass timber building; this is a building incorporating both steel and mass timber structural elements. It happens to have more timber than other buildings of a similar size, but it still has a lot of steel in it, so it is misleading to say it is a mass timber building. Notwithstanding the misleading marketing spin, I must acknowledge that it is a very nice building, and I look forward to an opportunity to look inside one day. If you google the building, you can see all those nice exposed steel structural elements adding to the ambience of the wood.
We are all entitled to market our materials and designs, and to be proud of our projects, but there is a need for accuracy and truthfulness, as well.
The panel spoke about the humidity and dimensional stability challenges inherent in mass timber design, and they spoke about the risk of moisture entering through the timber end grains. Of course, while I don’t know if the timber in this building was treated or untreated, these effects are generally mitigated through timber treatments – specifically through saturating the timber with the toxic forever chemical chromate copper arsenate (CCA). The use of such toxic chemicals brings long-term, generational environmental problems. The New Zealand National Institute of Water and Atmospheric Research (NIWA) notes that ‘toxic chemical contaminants and wastewater effluent from sawmills are significant environmental issues for the timber industry’.
While the carbon sequestration benefits of timber are widely touted, the truth is that trees do not lock carbon up forever; they simply ‘time shift’ it. They absorb carbon dioxide today and they release it tomorrow – and it is only through saturating the wood in toxic forever chemicals that it becomes possible to extend the time between absorption and release. It is those toxic chemical leachates, and the ultimate release of the carbon dioxide back into the atmosphere, that creates serious environmental problems for future generations.
This observation points to the somewhat paradoxical claims about the benefits of timber storing carbon in that while other materials, such as concrete and steel, emit carbon up front, and at much lower levels when recycled, at the same time the treated waste timber decaying in landfill will be releasing its carbon dioxide at an increasing rate.
In all likelihood, in 100 years’ time, the degradation of treated waste landfill timber might just be New Zealand’s single largest anthropogenic source of atmospheric methane and carbon dioxide emissions. That is the very essence of the problem of time-shifting carbon dioxide into our grandchildren’s and great-grandchildren’s century, and they are not going to look back and thank us for that.
The Co-Director of the University of Canterbury’s Wood Technology Research Centre was quoted in the NZ Herald as saying, ‘The suggestion that CCA-treated wood is a safe and environmentally friendly material is an insult to anyone’s intelligence.’
The emcee at the environmental conference I mentioned earlier reminded us of the Māori whakatauki about us being the kaitiaki of the land on behalf of future generations, and that we need to ensure our legacies do not become our grandchildren’s problems.
Steel is the only construction material that is infinitely recyclable with no degradation. This means that the steel in the ‘mass timber’ building’s structure will be recycled, as is current practice, at the end of the building’s life. Given steel is increasingly being recycled in electric arc furnaces (EAF), a process that produces only around 15 per cent of the carbon dioxide emitted by previous blast furnace processes, the low carbon EAF secondary path for the steel will bring benefits for those future generations when compared with conventional steelmaking.
Already EAF production constitutes approximately 30 per cent of global steel production, and this ratio is growing steadily, as is the adoption of renewable energy sources to drive the process. A local example of this is New Zealand Steel, which will have its own EAF up and running by the end of 2025, and it will run substantially on renewable energy, with the new plant reducing emissions by as much as one million tons of carbon dioxide annually. Furthermore, the plant will be supplied by New Zealand’s environmentally conscious metal-recycling industry.
In contrast, as the ‘mass timber’ elements of the building mentioned earlier are deconstructed at the end of its life, it will generate a pile of toxic treated waste timber that, again based on current practices, will most likely go to landfill, where it will break down over a long period of time, leaching out its chemicals while it releases its carbon back into the atmosphere.
So, returning to my opening points, there are no risk-free construction materials for our environment, and we must consider the overall balance and utility between timber, concrete, and steel.
This article is not about promoting one product over another, or about denigrating products. The intention of this article is to challenge some current embedded and unsubstantiated beliefs and guilt trips, and to have designers, specifiers, and clients take an objective, eyes‑open approach to product selection.
Humanity has yet to learn that short‑term solutions are not the fix for long-term problems; taking a short-term view will inevitably cost us in the long term. But its not all bad, as R Buckminster Fuller once observed, it was pollution that spawned the study of ecology and our eventual understanding of how our planet is an integrated system, and an understanding that effects are not always obvious, or geographically or temporally local.
Recent research undertaken by HERA, in collaboration with WSP and Aurecon, and supported by the Building Research Levy (published in SESOC Journal), indicates that construction can meet national carbon reduction targets through clever design and optimising the benefits of each material.
This research identifies the importance of designing for longevity, disassembly and circularity. It also identifies deficiencies in some life cycle assessment tools that produce biased outcomes through not including Environmental Product Declarations data associated with low-carbon options for steel and concrete that are readily available in the New Zealand market now.
Perhaps we should also introduce laws similar to those in some European countries where the manufacturer is required to take back and dispose of the end-of-life product – if so, I suspect that would be the last we hear about mass timber buildings, especially if designers and specifiers are also asked to share in that responsibility.
It is too late for most of us to go back to mud huts and thatched roofs, so we have to make choices and trade-offs based on full and objective data, and the recognition that no building product comes without environmental side effects, whether it be at the time of manufacture or at the other end of a product’s useful life. Let’s do this with eyes wide open and not have our objectivity hijacked by the spin doctors.