Using wood as a construction material for large buildings is an ancient practice. The 67-metre-high Sakyamuni Pagoda in China was constructed in 1056, while Japan's Höryü-ji Temple is even older, dating from the 7th or 8th century. That these magnificent structures have survived for over a thousand years is evidence of wood's strength and durability as a building material. Still today, 80% of houses in the USA are built of wood. In Australia the proportion is slightly smaller since stone is also a popular choice, particularly in the southern states, while in New Zealand the figure is more like 85%. Certainly, there are problems associated with wooden constructions: wood can rot when exposed to water and is said to be a fire risk. However, with modern technology these issues can be eliminated, which has led to a dramatic renewal of interest in wood as a building material in recent years.
Today, architects and engineers recognise the potential of wood not only for private homes but also for larger multi-storey offices and apartment blocks. In 2015, a 52.8-metre wooden tower block was constructed in Norway, then a world record for an apartment block, but this was soon surpassed by a 53-metre student dormitory at the University of British Columbia in Canada. Then came the 84-metre HoHo building in Vienna, home to a hotel, offices and apartments. Although the HoHo building has a concrete core, most of the structure as well as the floors are built of wood. Many of these advances have been made possible by research at the Technical Institute in Graz, Austria, where new engineering systems based on wood construction have been pioneered.
A good example of these techniques is found at the Wood Innovation and Design Centre at the University of Northern British Columbia, Canada. The first stage in the construction of the building saw large planks of Douglas fir being fastened to one another with glue, which these days can be stronger than nails or screws. This produced large heavy sheets of wooden material; these became the basic structural components for the building. These sheets then had to be precision cut to create the thousands of columns and beams necessary-the team employed lasers for this purpose. Once the cutting work was complete, all the wooden components were taken to the site for assembly. The building was constructed one storey at a time, layer upon layer, not unlike the system used to make a large cake. Once the eighth and final storey was completed, the building reached a height of 30 metres and became a notable landmark in its neighbourhood. And, of course, one of the great advantages of wood comes at the end of a building's life, in around 100 years' time. When the Wood Innovation and Design Centre eventually has to be demolished, it will be possible for its principal building material to be recycled, which is not usually practical with steel or concrete.
Other significant wooden buildings are to be found in locations around the world. Perhaps not surprisingly, given that the Höryü-ji Temple may be the oldest large wooden building in the world, Japanese engineers are at the forefront of this process. One thing that has been learned from maintaining the Höryü-ji Temple over many centuries is that it is often simpler to make major repairs to wooden structures than to those made of concrete and steel. Until quite recently, regulations in Japan have made the construction of very large wooden structures difficult. However, in recognition of new technologies, these are being relaxed by the government, with the result that ever more ambitious projects are being announced. Perhaps the most radical example is the proposed Sumitomo Tower, a skyscraper of 70 storeys to be built largely of wood in central Tokyo; its completion date is 2041.
Because wood is more flexible than steel, it has great potential in countries prone to earthquakes, such as Japan and New Zealand. Engineers in New Zealand believe that wood construction can significantly improve building safety in the event of a natural disaster, as has been demonstrated at the new Wynn Williams House. The wood has been left exposed inside the house to showcase how this type of construction provides attractive interiors as well. Another advantage of wood is that it is so light, particularly when compared to steel and concrete. In Australia, the benefits of light weight have been taken advantage of in the city of Melbourne, where a large wooden library has been constructed directly beside water, on land so soft that a heavier building would have been impossible. Furthermore, wood is advantageous even in extreme climates. In Finland, where winter temperatures can fall to -30°C, wood provides all the load-bearing structures for the Puukuokka Block, but also guarantees excellent heat insulation as well.
As wood construction technologies continue to develop, it seems probable that architects and engineers will dream up ever more uses for this practical, flexible and beautiful building material.