When discussion turns to sustainability - and ‘green buildings’ – EXPAN timber buildings using raw material sourced from renewable, commercial plantation forests are the clear winner. Using more timber in the construction of modern buildings – particularly where wood replaces significant quantities of structural concrete or steel in large or multi-storey buildings – is good for the environment, and significantly reduces greenhouse gas (GHG) emissions.
Conventional long-span and/or multi-storey buildings use concrete or steel as structural materials. A recent study for the New Zealand Ministry of Agriculture and Forestry (MAF) on the new 6-storey Biological Sciences building at University of Canterbury demonstrated that EXPAN buildings that use massive timber members - substituting a significant amount of conventional structural concrete and steel with engineered wood product (EWP) components - provide environmental benefits that are tangible, measureable and long-term.
EXPAN buildings – Good for the environment.
The raw timber for EXPAN buildings is sourced from carefully managed, renewable, commercial plantation forestry, which meets stringent environmental standards and certification and contributes significantly to supporting local communities.
Whilst EXPAN buildings use a lot of structural timber, overall they can make huge savings in quantities of materials to provide buildings which are light-weight (with significantly reduced concrete foundations). The study showed that EXPAN timber buildings had the lowest initial embodied energy and lowest initial embodied CO2-eq. for materials and, over the full 60-year lifetime of the buildings, the lowest total primary energy use and the lowest global warming potential (GWP).
Life Cycle Assessment (LCA) (ISO 14040) clearly demonstrates that EXPAN timber buildings are good for the environment because;
• Both the initial and full lifecycle carbon footprint of an EXPAN building is less
EXPAN timber buildings have the lowest carbon footprint.
Carbon footprinting of whole buildings using LCA provides an aggregated environmental impact (CO2eq. tonnes/m2) that includes all the materials that are used to construct a building and the full lifetime impact of that building, encompassing its operational phase and end-of-life. A comparison of the carbon footprint of one building with another demonstrates the benefit of using different building materials with regard to GWP.
In the studied example/s below, carbon stored in timber is included in the LCA and the defined end-of-life scenario for all materials (present-day landfilling practices in NZ) and the release of GHGs at end-of-life is accounted for completely. Since much of the carbon can be shown to be removed from the atmosphere permanently, this carbon storage forms a significant and enduring offset to carbon emissions from other parts of the life cycle.
Carbon footprint of Materials only (embodied carbon). See Fig. 1
The increased use of timber in the Timber building leads to considerably lower net CO2 eq. emissions than for the Concrete and Steel buildings. In the TimberPlus building, the carbon footprint for materials is negative and the carbon stored by the building’s materials more than cancels out all the GHGs emitted in the manufacture of all the other building materials combined.
Carbon footprint of buildings over full lifetime. See Fig.2
Over the full 60-year lifetime, which includes all the activities associated with the normal use of the buildings, the Timber and TimberPlus buildings maintain a clear advantage.
Advances in technologies and/or policy changes within New Zealand and internationally will mean that in the future there will be more importance placed on secure disposal, recycling and reusing deconstructed building materials, as well as being able to burn timber waste to recover energy. This will significantly reduce net carbon emission back to the atmosphere and will lead to an even greater improvement in the lifetime footprint of timber materials and timber buildings relative to concrete and steel.
Reducing energy consumption with EXPAN buildings.
When considering the energy consumed over the different stages of the full lifecycle of a building, this is dominated by the operational energy of running and using a building for many years, followed by the initial embodied energy of the building materials. The timber building’s materials have much lower embodied energy.
Considerable research leading to practical, commercial applications are dramatically reducing the operational energy of all new buildings. Timber buildings are being designed with very low energy consumption, rivalling that of both concrete and steel. Figure 5 shows that for the Biological Sciences building, there is little difference in energy consumption between the Timber, Concrete and Steel buildings over the life cycle. Continuing improvements in the operational energy efficiency of buildings means that the relative significance of embodied energy and emissions will increase, as these form a higher proportion of the total energy and emissions over the lifetime of a building.
For the Biological Sciences building, increasing the amount of timber decreased the initial embodied energy and decreased the total energy consumption over the building’s lifetime.
EXPAN timber structural components – renewable and sustainable.
The raw timber for all engineered wood products in EXPAN buildings is sourced from renewable, commercial plantation forests. When a tree in a commercial plantation forest in NZ is harvested, new seedlings are quickly re-planted and another mature tree will grow in its place, ‘powered’ by unlimited, solar energy - within 30 years, it too can be harvested and the cycle will begin again. No other structural building material is renewable in this way.
NZ commercial plantation forestry currently delivers over 20,000,000 tonnes of harvested softwood annually to industry. Good forest management and continual replanting of harvested areas means that this level of production can be not only maintained but increased in the long-term.
Forest certification guarantees the sustainability of NZ timber production, with today over 60% of NZ’s commercial forestry covered by strict forest certification regulations, such as Forest Stewardship Council (FSC).
Also and most importantly, the NZ Forest Accord (1991) is a unique agreement which recognises that development of planted forest should be in balance with preservation of natural forest; conservation groups accept the importance of plantation forests and agree to support sustainable plantation management, whilst forest owners undertake not to replace areas of native forest with new plantations
The forest products supply chain in NZ makes considerable use of thermal energy from timber waste, which greatly reduces the need to use non-renewable carbon-based fossil fuels. The manufacturers of NZ’s EWP use chain-of-custody (CoC) certification to not only ensure that all wood in its products is legally sourced from sustainably managed forests but also to provide the essential link between certified forests and timber processors, providing accreditation for responsible timber production across manufacture, wholesale and retail.
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