With a headline beginning ‘Not so carbon neutral now!’ the Daily Mail reported the Friday evening fire that destroyed the Carbon Neutral Laboratory for Sustainable Chemistry, a £15m building under construction at the University of Nottingham. Sixty firefighters battled the fire, and although they kept it from spreading they were not able to save the building. I’m very sorry to hear of this misfortune for former colleagues, not least because of the role that the building was meant to serve.
In one sense the Daily Mail is wrong: being largely a wooden building, it was carbon neutral: carbon dioxide is absorbed from the atmosphere when trees grow, and they lock it away. Later, when the wood rots away, or when it’s burnt, the carbon is released back into the environment. The loss of the building is a great shame, but it does demonstrate carbon neutrality.
Timber remains one of the best materials for sustainable construction, as becomes clear if we compare it to a common alternative such as working in concrete, steel and glass. Each tonne of steel, delivered on a building site but not including subsequent construction activity, has typically required energy totalling 15,360 kWh. (For recycled steel, a lower figure of 10,240 kWh may be used.) Similarly, the glass involves energy consumption totalling 8,960 kWh per tonne. Got a concrete base? That’s 3,200 kWh per tonne… and so on. It’s simple to measure embodied energy, and calculate the amount of carbon embodied in a building. (These figures come from Craig White of White Design, the Bristol-based sustainable architecture firm.)
The energy consumption in harvesting, seasoning, shaping and delivering a tonne of timber to site is just 640 kWh; far better than for any other commonly-used material – and it’s better still when you consider embodied carbon. Using wood actually has a negative carbon footprint because when you build a structure from wood you ‘lock up’ carbon that was absorbed during the growth phase. Despite the fuel used in harvesting and processing, some 500kg of greenhouse gas emissions are reversed when a tonne of timber is used.
The science bit
Alert readers might think that 500kg of CO2 being captured in a tonne of timber seems wrong. It can’t contain all that carbon dioxide, can it? Not exactly… but remember the oxidisation part: carbon dioxide emissions weigh more than the original fuel because during combustion, each carbon atom in the fuel combines with two oxygen atoms in the air to make carbon dioxide. The addition of two oxygen atoms to each carbon atom forms CO2 which has an atomic weight of 44, whereas carbon alone has an atomic weight of just 12. Thus, a tonne of timber represents far more than a tonne of potential greenhouse gas emissions. Even when we allow for all the energy used to harvest and process the wood into an architectural material, we’re left with -500kg of CO2 so it’s a superbly sustainable choice – as long as we replenish the wood that we use.
Barring incidents, it’s reasonable to assume that most buildings constructed today will still exist by 2050, and that means any wood we can put into use in this way will contribute towards efforts to slow climate change. The UN’s Intergovernmental Panel on Climate Change (IPCC) has set a target of limiting atmospheric concentrations of carbon dioxide to 450 parts per million. At that level it’s said that we have a fifty-fifty chance of holding the global average temperature increase to 2°C by 2050. Everything about this is uncertain (we don’t have sufficient previous experience to go on) but reducing the quantity of greenhouse gases that we emit is bound to be a good idea, in principle.
Is low-carbon always ‘green’?
Making everything out of wood is not a perfect solution to the mess we find ourselves in. Renewable timber resources typically come from managed forests, and they’re monocultures: plantations with equally-spaced trees of a single species, all at the same age. That makes sense if you’re in the business of harvesting timber for profit, but having a crop like that on your doorstep isn’t the same as having ancient woodland. As far as biodiversity goes, a timber plantation is practically a desert: you aren’t going to find anything like the wildlife population that is sustained in native forest… but are we interested in preserving native forest life, or fighting climate change? They’re both good goals, but they’re both different.
The spectre of climate change is a powerful argument in favour of greater commercial use of wood. Basically, you win twice: forests store 86% of the planet’s above-ground carbon, and 73% of the planet’s soil carbon (figures from Oregon Wild)… not merely while the trees live, but if harvested material is used sensibly, for decades to come –locked away in useful objects like buildings. Factor in that for any wood you build with, you’re using less concrete, steel and so on and you’re winning three different ways.
The transition away from concrete and steel isn’t going to be an easy one, and Britain doesn’t grow nearly enough wood. Things are getting better, though: ever since 1919 the nation’s forest cover has slowly increased. Wood is recognised as a strategic resource, and if you can’t get hold of enough wood for your sustainable building project, there’s always straw. A tonne of straw bales locks up 400kg of CO2 – in a ‘waste’ material that’s inexpensive, abundant, and has great thermal properties. (And if you prefer your building materials a little more engineered, have a look at Modcell for a straw-based prefabricated panel solution that puts ‘carbon-negative building’ within reach of ordinary businesses, not just those who are able to pay a premium for a ‘green’ image.)
Perhaps we are at the beginning of the Wood Age. It won’t always be simple, and there will be setbacks, but in terms of the architectural possibilities, the ‘green’ benefits and the cost savings, this is an exciting era. Meanwhile, I don’t doubt the University of Nottingham will recover from the fire, and go on to achieve good things in sustainable chemistry. Commiserations and best wishes.