Timber and Timber Products for Carbon Management
With the increased focus on the issues of climate change, timber has become an important contemporary building material in construction. The renewable nature and low impact characteristics of timber have attracted much attention in the building sector. Timber and timber products are lower in embodied energy and CO, emissions than the equivalent design using traditional building materials (Fraisse et ah, 2006; John et ah, 2011: Knauf et ah, 2015). In addition, they provide a carbon sink as a construction material, resulting in a potential reduction in the CO, concentration in the atmosphere (Schmidt and Griffin, 2012).
The low embodied energy characteristic of timber is important and case studies have recently been undertaken in order to compare the embodied energy and carbon impact of timber against heavier materials, such as concrete, bricks and steel, for structural elements in buildings. Some of the case studies are summarised in Table 2. From the case studies, research results demonstrate that timber construction consumes less embodied energy and has a carbon reduction benefit over those buildings using heavier materials.
The problems of climate change can be addressed by managing forests sustainably and using timber and timber products in buildings. Sustainable forest management (SFM) is a management process to ensure that trees continue to grow, absorb and store for an extended period of tune (Lippke et ah, 2011: Yan, 2018). The forest ecosystem is well recognised as critical in altering the atmospheric carbon concentrations of the global environment. Carbon emissions are highly receptive to land use change and proper management of forests can help to change the forest from a source to a sink (Carroll, 2012). The SFM is about managing and sustainably using the forestry in order to maintain the social, environmental
Table 2. Selected case studies of comparing embodied energy between timber and traditional materials.
and economic functions for all types of forests for present and future generations (UNFCCC, 2002: UNFF, 2007). SFM is crucial in ensuring a steady supply of raw materials for the production of timber products, however, the large scale of deforestation has hampered the timber reserves in the forest. According to FAO (2018), the world’s forest areas have decreased from 31.6% in 1990 to 30.6% in 2015. Therefore, as part of the SFM, afforestation and reforestation are two crucial strategies to restore the degraded forest and the related environment.
The use of timber and timber products can also be used to address climate change. Timber products convert forest into harvested wood so that they can continue storing carbon in large quantities for the duration of then useful life (Lehmann, 2013). According to Lippke et al. (2011), it is preferable that the timber be regularly harvested rather than left as a growing forest, as the harvested timber stores carbon for its entire useful life. Growing forests will remain carbon neutral as they absorb CO, dining their growth, but after they die and decay the carbon returns to the atmosphere. In addition, old forests slow the absorption of CO,.
The use of timber products, such as EWPs. can replace high emission intensity materials and alleviate environmental impacts (Lippke et al., 2011). The development of EWPs has shifted the use of timber from architectural to structural uses that are potential alternatives to traditional methods in the design and construction of buildings, in particular low impact buildings. EWPs such as LVL and CLT are now considered as sustainable building materials and systems that have the potential to turn buildings into carbon sinks if they are used on a large scale, replacing concrete and steel in construction (Lehmann,
The traditional RC structure is a high embodied energy design. The production of cement is a major energy consumption process in producing the clinker (Holtzhausen, 2007; Hossain et al., 2017). The production of cement contributes to approximately 5-10% of the total CO, emissions and consumes approximately 12-15% of total industrial energy use (Hossain et al., 2017). For the production of 1 tonne of cement clinker, approximately 0.87 tonne of CO, is released into the atmosphere. Steel production is also high in both embodied energy and emissions. The embodied energy required in the manufacmriug of steel includes the extraction of iron ore then melting it in a furnace with oxygen to remove impurities and reduce carbon content. According to Quader et al. (2016), the production of 1 tonne of steel generates approximately
1.8 tonnes of CO,.
In addition, there is significant scope for higher carbon storage in houses by increasing the use of timber and timber products for the construction of sub-floor and wall cladding systems. As an example, doubling the wood used in houses to 0.14 m3 per nr of floor area would result in additional axmual carbon storage in houses in Australia from 1.6 Mt CO,-e in 2008 to 4 Mt CO,-e in 2050 (Kapambwe et al., 2008).
Holtzhausen (2007) estimated that only around 0.098 tormes of CO, are emitted from every gigajoule of embodied energy consumed in timber. The displacement of CO, has been estimated for the use of timber instead of material alternatives to the order of 3.9 tonnes per tonne of timber used (Satlire and O’Connor, 2010). Estimates of carbon sequestration are around 1 tonne per metre cube of timber (Lehmann. 2013). Therefore, in comparison to the traditional heay materials used in the construction of buildings, timber and timber products are more environmentally friendly materials. Lippek et al. (2011) state that replacing steel joists with approximately 1 tonne of engineered wood joists can cut down CO, emissions by about 10 tormes. In addition, for every tonne of wood flooring used to replace concrete floor. CO, emissions can be reduced by approximately 3.5 tormes.
Availability and advancement of EWPs, powerfi.il lifting, transport equipment and use of high precision production facilities enable the use of prefabricated timber elements, which can span longer than traditional systems (Kolb, 2008). However, compared to concrete and steel building construction, there are also several challenges. Some of the significant challenges are fire performance of timber building, lack of information and evidence relating to constructability and technical guidelines, i.e., (pre)fabrication and standardised connection details, particularly for mid- to high-rise non-residential buildings. In addition, the supply chain for timber is not as well-organised as for other heavy building materials.
The permitted number of storeys or storey height of mass timber building is different in different countries, depending on the local regulations. Before 1994, some countries in Europe restricted the use of timber for load-bearing structures of more than two storeys due to fire regulations (Falk, 2005). However, several countries in Europe now have no specific regulations or do not limit the number of storeys in timber buildings (Ostman and Kallsner, 2011). In the United States, the development of new technologies and innovation in wood framing designs have permitted the construction of timber buildings up to four storeys, depending on the occupancy classification and the presence of automatic sprinkler systems (American Wood Council & International Code Council, 2015). Before 1992, timber structures were limited to three storeys in New Zealand, but changes in the Building Code since then have increased both the number and size of multi-storey timber buildings (Banks, 1999). Since May 2016, the Australian National Construction Code has permitted the use of timber framing for buildings in Class 2 (apartments) and 3 (hotels) up to 25 metres height (approximately 8 storeys) under deem-to-satisfy provisions. This code change creates a significant opportunity for the development of the commercial timber building industry in Australia.
There is no doubt that timber is environmentally, aesthetically and health-wise an ideal choice of material. However, its usefulness will rely on the sustainable supply of raw materials. Therefore, forestry and acquisition of raw materials are important elements in the long term to ensure logs are sourced from sustainable plantation forests. Davidson and Hanna (2004) state that softwood timbers, such as Radiator Pine, are cheap and easy to process and are the primary product used in the production of EWPs. As such, their supply will, in turn, influence the potential output for the EWP industry.
The case studies in Section 6 have demonstrated the possibility of using EWPs in mid- and potentially large-scale buildings. However, research studies also indicate that there are limitations of EWPs and these may har e hindered the uptake of the EWPs. The main issues are related to the lack of confidence and knowledge among professionals in the design and construction of large buildings using timber (Holmes et al., 2011: Thomas et ah, 2014). In addition, there is a negative perception of timber in relation to durability, fire, acoustic, thermal performance and durability (Gold and Rubik, 2009; Nolan. 2010; Roos et ah, 2010). These obstacles are viewed as difficult to overcome when timber construction is specified. Furthermore, the lack of confidence in using timber stems from a multitude of issues, such as lead times, cost implications, connection details, availability, commercial risk, lack of assistance and poor marketing (Holmes et ah, 2011). However, some of these negative perceptions conflict with research into timber performance in areas of durability, fire, acoustic and thermal performance (Papadopoulos et ah, 2008; Lennon et ah, 2010; Ruben et ah, 2011). Structural performance and termite resistance are governed by building codes and standards that dictate minimum performance for all buildings regardless of building material selection.