Wood forms a central plank in nearly-zero energy buildings
Efforts to tackle climate change must occur on all fronts. The construction industry is responsible for around 8 % of the world’s CO2 emissions. Can a change in building materials help reduce its impact? The EU and EU national policies have stepped up efforts to combat climate change by boosting wood construction. Wooden buildings can result in 50 % reduced greenhouse gas (GHG) emissions compared to conventional buildings with steel and concrete structures. One way to achieve this is with wooden nearly zero-energy buildings (NZEBs). The EU-funded NERO project collected and identified best practices and technical solutions that significantly reduce the costs of wooden NZEBs in four different seasons. “The growing use of wooden products in buildings gives us a material that is light, durable, and more local. Unlike concrete, wood offers a circular material that can be taken from old homes and reused in new ones, and acts as a long-term carbon sink,” explains project coordinator Tero Hasu. The project team collected construction costs, implementation and operational energy data examples of carbon emissions from 17 demonstration buildings, 11 of which were already completed, and with six demos being planned and mainly completed during the project. Life cycle assessments (LCAs) of the case and demonstration NZEBs were conducted to analyse the environmental impact of representative NZEBs in partner countries. Such information was used to compare technical solutions (e.g. structures and envelope systems) among the buildings to identify the areas of potential abatement of embodied emissions and energy.
A look at two of the case studies
In one case study in Växjö, Sweden, where wooden public buildings have been a top priority, NERO developed multifamily buildings one step further. Project findings showed that the national NZEBs could offer 30-40 % lower delivered operational energy use than stipulated by the existing national building code. The LCAs showed that wood-based buildings offer a significantly lower production stage primary energy use and lower carbon footprint than non-wood alternatives. Cost-optimal analysis showed thicknesses of insulation to achieve the NZEB energy level are considerably higher than required to meet the minimum energy requirement by the code. Implementation of the NZEB solutions results in economic benefits, but not as much as the implementation of cost-optimal solutions. In another case study in Trondheim, Norway, an analysis of the case and demonstration NERO buildings showed that replacing concrete with wide use of cross-laminated timber for structural elements was deemed important, with at least a 30 % reduction in GHGs. It is expected that a large uptake of such a construction technology in the Nordic market will reduce these costs. “The trend for the near future is clear. At least here in the north, an increasing number of main structures for new buildings will be made of wood,” concludes Hasu. In the long run, prefabrication and industrialisation of production coupled with a lean process at factories and existing supply-demand balance on the market through a wider market uptake will bring the biggest emissions reductions. Also, near-future recommendations, guidance and legislation for emissions allowed in construction will yield the same results. The benefit from reducing the amount of concrete was evident in the NERO project where LCA was defined. Today, however, having only a carrot without a stick, the benefits are difficult to quantify in terms of societal cost savings.
Keywords
NERO, NZEB, climate change, wooden buildings, construction industry, Northern climatic conditions, nearly zero-energy buildings
