IS BUILDING WITH WOOD SUSTAINABLE?
How can wood, as a building material, reduce the impact that buildings have on the environment?
The construction sector has a major impact on the environment due to the high consumption of resources and energy for the construction and operation of the buildings that we conduct our activity in dwellings, offices, commercial and industrial areas. According to European Union’s statistics, buildings are responsible for 40% of energy consumption and for 36% of CO2 emissions, the highest percentage compared to the other sectors. We have written more on the impact of buildings on the environment in this article.
Over the past years, there have been endeavors towards reducing buildings’ power consumption, such as the nZEB (nearly Zero Energy Building) standard and the Passivhaus standard ( passive house), but if we look at things in perspective, diminishing carbon emissions is not enough.
What is to remember is that a building takes considerably larger quantities of energy to be built, than to be operated. Imagine how many types of materials are used: concrete, steel, brickwork, shuttering, casing, carpentry, finishes, furniture…and the list goes on. Now think about the manufacturing process for each one of them, from the quarrying of the raw material to the manufacturing process and putting them into practice. All these processes take the energy that comes in overwhelming proportion from conventional sources. ( coal, gas, oil).
And we reach the elephant in the room: wood as a building material. Although it may seem counterintuitive that by cutting trees, we protect the environment, in reality, things are different and we will give arguments hereunder.
A tree's life cycle
Wood is a natural material that can be found abundantly in nature and that is, more importantly, renewable. Building with wood is sustainable because the raw material, namely the tree, regenerates at a certain time, depending on its type. Like any living organism, a tree has a life cycle: it is born, it grows and it dies, then it is integrated back into nature.
Let’s take the example of spruce, the most spread type of softwood tree. Spruce forests cover almost 22% of Romania’s forested area and offer a wooden mass with very good properties for civil constructions, such as timber-frame houses.
Through photosynthesis, sapling spruce grows rather slowly by the age of 10-15 years, followed by a quick vertical development until the age of 30 and it then grows in diameter until the age of 50-60. Until it is 80-90 years old, the growth slows down and reaches a point where it stagnates. In this phase, the spruce can reach 50m in height and a diameter up to 1.5m, depending on the climate conditions of the area. All this time, the tree absorbs CO2 from the atmosphere through photosynthesis and it firstly uses the carbon as nourishment for its development and then as nutrients for the soil, playing an essential role in the carbon circuit in nature.
Once it becomes old, the tree liberates, through breathing, more carbon dioxide than it can absorb through photosynthesis and it begins to deteriorate, being attacked by other living organisms. Hiking and forest lovers can give endless examples of fallen trees found in their path.
Hence, the exploitation of ripe trees is perfectly normal and it does not have a harmful impact on the environment. In the case of the spruce, the exploitation period is 90-110 years old. All this time, 4-5 saplings can grow around an old tree, saplings which are halved after 10 years and after 50-60, only 2-3 are left so they do not suffocate each other.
Wood as a building material is an everlasting renewable source if the forests are exploited sustainably. Ripe trees that can no longer absorb CO2 are cut and, in their place, saplings that will enter the previously described circuit are let grow.
Why building with wood is sustainable
As opposed to the rest of the building materials, wood is the only renewable material. Steel, brick, or concrete come from finite sources, while wood only needs time, water, sun, and nutrients from the soil to grow and to produce cellulose, the basic compound that gives it value as a building material. On average, 1 CBM stores 900-1000 kg of CO2. 30% of the carbon ends up in the soil, while the rest is used as “nourishment” during the growth period. The exploiting and manufacturing processes of the log in order to be turned into lumber take the energy of their own and have an associated carbon footprint, of approximately 200-300 kg of CO2. On the whole, 1 CBM of wood stores 600-700 kg of CO2.
On the other hand, conventional materials need more elaborate processes to extract the raw material and to turn it into the final product, as they take a lot of energy.
For instance, a conventional house of 150 square meters takes on average 80-90 m3 of concrete and 13-14 tonnes of steel for fittings. Without counting brickwork, we have almost 60 tonnes of CO2 just for the resistance structure. On the other hand, a similar timber-frame house takes around 40 m3 of wood, so 16 tonnes of carbon dioxide is absorbed from the atmosphere and stored into the structure of the house.
Unfortunately, in Romania, wood as a building material is not regarded very well due to the uncontrolled exploitation and sale as a log on export without added value. More than that, a significant part of the cut wood is firewood, which makes things worse from the climatic point of view ( all the carbon dioxide absorbed by the tree is released back into the atmosphere through burning).
This situation ruins the reputation of an extraordinary building material with a high potential of reducing the impact that buildings have on the environment. For example, France requires that new public constructions be built with at least 50% wood or other organic materials ( hemp and straw) and in the last years, such measures have been adopted by more and more Occidental countries.