Although it may seem counter-intuitive, it would be better if we built buildings from wood than from concrete, brick, aluminium and steel.
We use millions of tonnes of these modern materials every year. They have many valuable properties, but are energy-intensive to create, accounting for around 16% of the entire planets' fossil fuel production. Instead we could be using wood, which is also strong, renewable, and plentiful – we use only a fraction of the world’s available forestry resources.
Our research, published in the Journal of Sustainable Forestry, estimated that the world’s forest contain about 385 billion cubic metres of wood, with an additional 17 billion cubic metres growing each year. A mere 3.4 billion cubic metres is harvested each year, mostly for subsistence fuel burning; the rest rots, burns in fires, or adds to forests' density.
Swapping steel, concrete, or brick for wood and specially engineered wood equivalents would drastically reduce global carbon dioxide emissions, fossil fuel consumption and would represent a renewable resource. What’s more, managed properly this can be done without loss of biodiversity or carbon storage capacity.
In our study undertaken by scientists from the Yale School of Forestry & Environmental Studies and the University of Washington’s College of the Environment we evaluated various scenarios including leaving forests untouched, burning wood for energy and use of wood as a construction material.
The 3.4 billion cubic meters of wood harvested each year accounts for only 20% of new annual growth. Increasing the wood harvest to 34% or more would have several profound and positive effects. Emissions amounting to 14-31% of global CO2 would be avoided by creating less steel and concrete, and by storing CO2 in the cell structure of wood products. A further 12-19% of annual global fossil fuel consumption would be saved, including savings from burning scrap wood and unsellable materials for energy.
Building with wood consumes much less energy than using concrete or steel. For example, a wooden floor beam requires 80 megajoules (mj) of energy per square metre of floor space and emits 4kg CO2. By comparison, a square metre of floor space supported by a steel beam requires 516 mj and emits 40 kg of CO2, and a concrete slab floor requires 290 mj and emits 27kg of CO2.
By using efficient harvesting and production techniques, more CO2 is saved through the avoided emissions, materials, and wood energy than is lost from the harvested forest – yet another reason to appreciate forests, and to protect them from endless deforestation for agriculture. Clearing trees for harvest is temporary, but converting forests to farmland is a permanent loss of all forest’s resources and biodiversity.
If transport and assembly is taken into account, the 16% of global fossil fuels used to manufacture steel, concrete and brick is closer to 20-30%. These potential fuel and carbon emissions savings, already substantial, will become increasingly critical as demand for new buildings, bridges and other infrastructure surges with economic development in Asia, Africa and South America.
At the same time, new construction techniques have made wood even more effective as a building material for anything from bridges to mid-rise apartment buildings. The cross-laminated timber increasingly used in new buildings, made from alternating layers of perpendicular, wood pieces has strength approaching that of steel.
In 2009 a nine-storey building, Stadthaus, in London, was built with CLT instead of steel construction and in Stockholm a 34-storey wooden building has been given planning permission. There are many others, already built and in the pipeline.
Harvesting also reduces a forest’s likelihood of suffering a catastrophic wildfire, and improves its ability to withstand it. Maintaining a mix of forest habitats and tree densities in non-reserved forests would help preserve the varied biodiversity in ecosystems worldwide. Harvesting wood will save fossil fuel and CO2, and provide jobs – giving local people more reason to ensure the forests' survival.