Materials cannot be separated from the specific building performance and context, and to do so is taking a simplistic view, writes Nigel Howard from Clarity Environment.
Climate change is the most pressing existential threat to our species and should always be the central issue in any environmental or sustainability discussion with all other issues secondary. Loss of biodiversity is the second existential threat, but this is predominantly caused by climate change now (not just land use).
The main cause of climate impacts is energy use. For buildings, this is dominated by electricity used for heating, cooling, lighting, hot water and power; for infrastructure it may be about how the design affects the efficiency and utilisation of vehicles. Materials tend to be relegated to tokenistic consideration, with designers adopting simple rules of thumb or slogans to inform their choice or post-rationalise an aesthetic decision.
For buildings, we should fully consider how materials are used to respond to the climate at the location and minimise heating, cooling, ventilation and artificial lighting, while maximising daylight and views. Glazing, orientation and shading (horizontal louvres or deciduous planting) can be strategically used to benefit from winter heat gain where needed but not summer heat gain when not needed. Vertical shading is purely aesthetic.
All of this depends on the uses contained by the building. The materials cannot be separated from the specific building performance and context – all else is over-simplification. Embodied impacts are often overstated. What’s needed is a tool that can reveal all of the perverse outcomes and tradeoffs in design decisions from inception, as the decisions are made.
For infrastructure, having chosen which infrastructure to build – for example road versus rail and which routes to take, the embodied impacts over the life of the project are more important.
For simple stuff like roads, route design to minimise cut and fill is important, as is using materials locally sourced (including recycling crushed concrete on-site) to minimise transport. This is project specific.
Reusing crushed concrete as aggregate in new concrete is not necessarily a good idea, because crushed concrete does not compact as effectively as natural aggregates, perversely requiring more high impact cement to achieve the same structural strength.
For complex infrastructure – bridges, tunnels, dams, etcetera –there are no simple reliable rules of thumb, yet innovative structural engineering and concrete mixes are achieving surprising performance.
We have dumbed this all down for rating tools and Ecoprofiles which are of little to no real value for informing best material choices, except between substantially similar products/materials (that is, they are no good for steel versus concrete versus timber).
If I were to make one generalisation it would be that timber is generally a winner as a material because it is naturally thermally insulating, it is strong for its weight and sequesters CO2 for its life. We need to be reafforesting not deforesting and using timber productively and then getting the carbon back into the soil. The one little Achilles’ heel for wood is that in buildings it emits formaldehyde – a carcinogen, but this bakes out quite quickly. No one likes to talk about that because wood has so many other benefits, so it gets special treatment in rating tools (it shouldn’t – instead the effects should be explicitly quantified and appropriately weighted for significance).
For the same structural purpose (beams or columns) wood generally beats concrete, which generally beats steel. But this is not a reliable rule of thumb. Concrete frames use a lot of reinforcing steel and steel often uses a fair bit of concrete for fire protection – sometimes it’s even hard to tell. Steel pretends to beat concrete by cheating on the methodology (the IISI methodology) and counting the anticipated benefit from thousands of years of future recycling as though it was already happening – on current trajectories we will be extinct as a species before the benefits already claimed are ever realised. If Ecoprofiles users want to get a more reliable result, then they should reduce the Module D credit claimed for Australian steel from about 40 per cent to about 5 per cent to correct the data.
This may be about to change radically if Sanjeev Gupta shakes things up enough. But at present, his plans seem to amount to trading-off the impacts of Whyalla against displaced grid electricity rather than actually reducing the emissions from BF/BOS steel! We need solar-powered hydrogen or direct reduction of ore for a truly innovative decarbonised steel.
Nigel Howard founded the Edge Environment Consultancy in Manly and is now sole trading as Clarity Environment and trying to complete and commercialise his pet project intermittently developed for 30years – ENVEST
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