Photo: Gabriel Giacometti
Technological innovation in modern wood construction derives from material science and structural engineering, from the testing the properties of different types of materials and wood products in relation to stability, vibrations, fire-safety, acoustics, energy efficiency, and so forth. Moreover, technical, and technological innovations also include industrial processes, architecture and design tools, transport, and supply chain innovations. Significant efforts have centred around developing building systems and the industrialisation of construction (The Lean construction method). As a result of the ‘green agenda’, increased focus has centred, in recent years, around new ways of designing for assembly and disassembly, considering the life cycle of buildings, their transformation over time, and their ‘end-of-life’. We focus more specifically on building systems and industrialisation processes as follows.
There are different construction techniques and systems used to build with wood. Important differences have to do with the degree of prefabrication and the types of wooden products and combinations of materials used. Conventional construction generally implies work done mostly onsite, the use of traditional materials, and a low level of industrialisation. In many high-income economies, however, conventional construction also implies the use of industrialised or prefabricated building elements. Prefabricated (or prefab) elements, such as frames, columns, and slabs, are produced in a factory and assembled onsite. To varying degrees, most buildings in industrialised economies today build portions of their structures in a factory setting. While wood is a traditional construction material, multi-storey wood buildings still represent an outlier. Innovation in wood construction has pushed the industrialisation process forward, with both modular systems to produce prefab volumes, and wood-engineered products to create prefab frames and other building elements. According to Nord (2008), there are roughly three levels or methods of prefabrication in the production of multi-story wood buildings: 1) onsite construction using pre-cut components, 2) assembly onsite using prefab timber elements, and 3) assembly onsite using prefab and pre-assembled timber volumes (Figure 2).
Figure 2: Construction methods in relation to the degree of prefabrication. Source: Nord (2008).
In Sweden, about 97% of all multi-storey buildings with a wooden frame have been completely or partially prefabricated by 2020 (Swedish Forest Agency 2020). In modular systems, most components are prefabricated offsite and assembled onsite to produce volumes, resembling human-scale LEGO. Prefab modular construction can reach the level of manufacturing ready-made rooms or sections of apartments, including electrical installations, heating, plumbing, and air-conditioning systems in a factory setting (Manninen 2014). Other systems use prefab frames and building elements similar to conventional construction but replace concrete-steel elements with structural wood engineered products or mass timber such as glue-laminated timber (Glulam), cross-laminated timber (CLT), and laminated veneer lumber (LVL). (Refer to Info Box 1 for definitions).
Different building systems and wood products have their own uses, advantages, and disadvantages. Wood is a light, structural material, with a low or negative carbon footprint, and is vastly available in the Nordic countries. Modular construction in wood moves most of the construction work offsite, to a factory setting. Systematising the work in a factory setting has numerous advantages. It provides a dry and predictable working environment, while minimising the possible problems of climate or accessibility to the site; it reduces disturbances to the public around the construction site; it allows for a different organisation and better coordination of the work with fewer sub-contractors, as more workers are employed at the factory instead of providing services onsite; and it radically cuts the time of work onsite, making it possible to assemble a high-rise building in the span of a few months. All these benefits also result in lower costs of production/construction. Because of these attractive advantages, the growth of modular wood construction as an industry is now comparable to electric cars in speed, growing from € 20 million to almost € 100 million in a few years (Interviewee 2). A commonly known disadvantage is that prefab modules limit the flexibility of architectural design (Interviewees 1, 6; Brege et al. 2013). However, this limitation may be less related to the technical possibilities offered by modular systems and more to transport restrictions (as lorries cannot carry units of any shape and size), or to decisions made at the design stage before considering the option of using modular systems, rendering it too late in the process (as modules can potentially be built in any shape). In any case, modular construction is a top alternative when speed and cost efficiency are prioritised over architectural expression: for instance, when municipalities or regional authorities wish to rapidly increase hospital beds, elderly care homes, schools, or affordable homes. Modular construction comes handy in delivering high volumes efficiently in a competitive and cost-efficient way (Interviewee 2).
Furthermore, the introduction of engineered wood products has added versatility in the use of timber in construction, making it possible to build larger structures, which are light, structurally sound, and energy efficient, among other positive qualities. One expert view is that the introduction of CLT represents a radical innovation in the sense that it has enabled the construction of large wooden buildings. At the same time, CLT allows designs similar to conventional buildings, requiring no major deviations in the design process (Interviewees 1, 11), making the innovation decisively less disruptive.
As the market develops, the focus is shifting from building exclusively with wood-base systems to also incorporating opportunities for hybrid construction systems and materials: mixed wood products, or wood with steel, concrete, recycled materials, or new innovative materials. For instance, non-bearing walls can use lighter, material and space-efficient alternatives instead of structural materials such as CLT. It is also possible to combine building systems, as in the case of the SARA Cultural Centre in Skellefteå, which was built using a glulam frame combined with CLT modules in the hotel units.
Finally, several experts coincide that besides the development of construction systems, the industrialisation of wood construction represents a breakthrough, making it possible to build in scale, reach higher production volumes and move from a niche market to compete with conventional construction. By applying the principles of ‘lean construction’ and ‘lean manufacturing’, industries have optimised the workflow in production facilities enabling them to cut costs and produce in higher volumes. Lean manufacturing or ‘lean production’ is a methodology or practice first applied in the post-war by the Japanese automobile company, Toyota, aiming at increasing productivity via continuous improvements in the production system. It maximises value by minimising ‘waste’ both in terms of material resources and superfluous processes, activities, work, and time spent in the production system. Lean construction uses these principles to make the process of building considerably more efficient, saving valuable time. The main principle of lean construction is to reduce all work phases that do not produce added value to the customer, for instance, decreasing waiting time at the construction site (Rakennuslehti 2016).