Frank Werling of Finnish wood specialists Metsä Wood says the green agenda in construction must shift towards sustainable production of building materials – and timber leads the way as an alternative to steel and concrete.
A brief history of timber
Timber is the oldest building material known to man. Since the dawn of construction, when early hunter-gatherers used wood and rudimentary tools to build shelter, through to modern times, timber remains one of the most important and versatile construction materials available.
In comparison, steel and concrete have only found their way into construction over the past 250 years, and despite being the construction materials of choice ever since, timber is now enjoying a resurgence. With the dawn of engineered wood products (EWP) such as Laminated Veneer Lumber (LVL) during the second half of the 20th century, the dimensional restrictions related to tree growth have disappeared. Today, with the inherent predictability and accuracy of physical properties, timber products are now finding their way back into construction.
Light and strong
Building with LVL from the ground up, makes the structure significantly lighter when compared to traditional choices like concrete and steel. The lighter weight of the building materials means less pile-driving and earth-moving when preparing the foundations. When the components are pre-fabricated it also means transportation to site and the actual building process costs significantly less because there are fewer building elements.
LVL is not only light but also extremely strong. The weight-strength ratio of a building material can be expressed in the length a rod of material in tension before it ruptures from its own weight. For concrete this is approximately 0.5 km – and for steel approximately 5.0 km. LVL can achieve one of the highest available strengths for any EWP with approximately 12 km.
The excellent strength-to-weight ratio of LVL enables long spans of up to 25 m. Other benefits of building in timber are that it is warm to touch, i.e. it does not transfer the heat away. Furthermore, it can be used as an effective insulation material as the heat is retained. It also means if it catches fire, it insulates the structure from the fire. Much has been made of the fire risk of timber, however, the rate of charring for timber is very predictable whereas the heat of a steel element cannot be established. Therefore a timber element protects itself in a fire whereas steel requires additional safety measures.
Case study: Achieving energy self-sufficiency through bio heating
A significant part of global energy consumption is eaten up by the production of steel, aluminium and concrete. Wood, however, is an extremely sustainable alternative.
LVL uses as much of the wood as possible. Part of the sawdust and wood chips that are generated in processing the engineered wood are used in pulp production but also in bio energy. An example of this can be seen in the running of the Metsä Wood Mill in Lohja, Finland, which produces LVL. At Lohja, a bio heating plant has been built next to the mill in order to capture the full potential of the production. The heat energy produced at the plant covers the needs of the mill, resulting in complete energy self-sufficiency.
At the same time, the remaining heat from the production process is sold for district heating to the town of Lohja and provides significant support for reaching the town’s ambitious low carbon energy goals. Lohja is part of Finland’s national scheme to reduce greenhouse gas emissions by 80 per cent by 2030. And thanks to the bio heating plant, it has already accomplished its first milestone in achieving a 15 per cent reduction of greenhouse gas emissions by 2016. In addition, as the side streams of the LVL production, (bark and woodchips), are utilised at the same plant, traffic emissions are reduced as well.
A greener future in construction
The focus of improving efficiency has to shift from the energy used to operate a house to the production of the construction materials – which is the most energy intensive phase in a building’s life cycle. The energy required to produce the materials of a building is 50 times more than the energy used to operate it for a year. Since the production of wooden materials results in an energy surplus, the implications are clear: wood should be used whenever possible.
Designing in wood
The use of timber in modern architecture is something that is becoming more widespread, with students now being educated in these new sustainable materials. Metsä Wood is at the forefront of supporting this educational process, and through its Plan B programme the company is working with architectural students and industry to explore the possibilities of using wood in urban construction.
One recent example of this is Metsä’s City Above the City design competition, which is looking for bold and ambitious plans that connect wood construction processes to an existing urban context – in a way that is friendly to both people and nature. Entrants have been challenged to select a centrally-located building in one of the world’s most populated cities and develop an innovative wood design solution that adds density through additional floors. Building additional floors with Kerto LVL as the primary material is a central requirement for the design work.
Frank Werling is head of technical, engineering and design at Metsä Wood.