Is it sustainable to build houses from wood?

Trees absorb carbon dioxide, so is it sustainable to be cutting down all these trees to put in buildings? Shouldn’t we be leaving them alive in the forests? Iacopo Russo put some of those concerns to Will Hawkins, a structural engineer at the University of Bath, who specialises in efficient and sustainable buildings...

Will - When we're talking about replacing most concrete and steel structures with timber, most people would agree that using timber is better than the alternatives.

Iacopo - But we often hear that planting trees can help oppose climate change because trees absorb carbon from the atmosphere, so they help offset the carbon we emit elsewhere. Can storing carbon in timber buildings also help oppose climate change?

Will - I think the way to think about this is the total benefit in terms of timber products can be thought of as the total amount of CO₂ that's stored in both the forests and the products. By making buildings and locking away CO₂, you're increasing the store in timber products, but you have to make sure that by doing that, you're not just creating a equivalent production in the forest. The key is to do this in a way that keeps the forest carbon storage high whilst creating new timber products and a new storage of carbon alongside it.

Iacopo - Is it better to store timber in buildings for the environment?

Will - It's better to use timber for products that are gonna last a long time. Buildings have a really good advantage in that respect compared to something like fuel or packaging. We also need to consider what that timber is displacing. So for buildings we'll be displacing steel and concrete, which we've already heard are quite highly emitting, but also we could be using that timber to replace fossil fuels, or we could be using it to replace plastic packaging. So it's not necessarily obvious. Timber is always doing good whenever we're using it by displacing something else, and it appears as though buildings are going to be one of the best ways that we can use it.

Iacopo - But at the same time, growing trees for that timber to store carbon in buildings requires land, and we already need land for many other things like growing food. Is there going to be a problem with how we manage land in the future?

Will - Our use of land is one of the key causes of biodiversity loss and if we use it for anything else, then something has to go. Usually that's the natural world. We always have to make a choice and make a compromise and unfortunately when it comes to timber evidence shows that the more productive or the more timber is harvested from a forest generally the lower its biodiversity tends to be. But timber plantations are often grown on less fertile soil, so upland areas. So there is scope to create new timber plantations in places that are not already that productive for agriculture.

Iacopo - I suppose one thing we need to worry about is what happens to timber buildings after they're demolished, what happens to the timber?

Will - The majority of timber waste in the UK is actually burned as biomass. It goes into producing electricity that offsets production from the grid, but also you're re-releasing that CO₂ straight away. The rest is down-cycled into either chipboard or MDF or even animal bedding or compost. So again, we're going from timber structure, which can store biogenic carbon for a long time, into products that generally have a much shorter life and that biogenic carbon is generally being rereleased quite quickly.

Iacopo - There seems to be a lot of different aspects to consider, what would you recommend we should do overall?

Will - I think our first priority is to just consume less. We need to question whether we need new buildings at all and we need to reuse existing buildings as much as possible as a priority. Then if we decide that we do need a new building, the focus needs to be on material efficiency. There's ways that we can create buildings that use a lot less materials. We can make the spans shorter, or we can make clever shapes so that they're inherently strong and we don't need to use lots of material. Finally, the last thing to do is to replace the concrete with the timber, but we really need to make sure that we're using only the smallest amount of timber that we can get away with because those forests are already under pressure and wherever timber is used, it does good.