Byggnadsintegrerad växtlighet som klimatåtgärd : En analys av kolbalans mellan biogena utsläpp vid virkestillverkning och koldioxidupptag i en träbyggnad

Sammanfattning

The building and real estate sector accounts for a significant share of Sweden’s climate impact, which has contributed to a growing interest in timber construction as a more climate-friendly alternative. At the same time, timber construction involves the combustion of residual products from timber manufacturing, resulting in immediate biogenic carbon dioxide emissions. These emissions occur instantly, while carbon uptake in biomass takes place gradually over time, creating a temporal mismatch that is rarely made visible in conventional climate assessments. In parallel, nature-based solutions, including building-integrated vegetation, have received increasing attention as complementary climate strategies in urban environments, primarily due to their ecosystem services such as stormwater management and temperature regulation. However, whether such vegetation can also contribute to balancing biogenic emissions associated with timber construction remains a question with limited quantitative evidence. This study aims to contribute to a better understanding of the extent to which building- integrated vegetation can balance biogenic carbon dioxide emissions resulting from the combustion of residual products generated during the timber manufacturing process for a specific building, through a combination of a literature review and a case study. The case study is based on an existing four-storey cross-laminated timber building in Malmö. Emissions are calculated based on the building’s actual material volume and compared with the theoretical carbon uptake of vegetation over the building’s 50-year service life. Three climbing plant species are analysed: English ivy, Boston ivy and Russian vine. In the baseline scenario using English ivy, with a biomass growth rate of 0.12 kg m!"year!#, the maximum available façade area amounts to 891 m", while achieving carbon balance would require 6,718 m". The compensation rate reaches 13 % in the baseline scenario and 71 % in the strongest scenario, where Russian vine is tested in a sensitivity analysis. In the baseline scenario, balancing all emissions is estimated to take up to 400 years, highlighting the fundamental challenge of relying on biological carbon sinks as a climate mitigation measure. The climate benefit of vegetation lies in delaying climate impact rather than eliminating it. Carbon storage in biomass is reversible and time-limited and the results should therefore be interpreted as a complementary climate contribution rather than full compensation. The visual design proposal demonstrates that green façades with climbing plants can be integrated into the building while considering its existing architectural design and the local conditions in Malmö. The choice of plant species and degree of façade coverage influence both climate benefit and architectural expression. Fast-growing species provide earlier visual results but also involve increased maintenance requirements and greater uncertainty regarding long- term climate benefits. This study contributes quantitative evidence on how building-integrated vegetation can be assessed as a climate measure in timber buildings and provides a methodological example of how biological carbon uptake can be quantified and related to specific biogenic emissions from timber manufacturing. The findings are primarily applicable to similar buildings in urban environments in southern Sweden. Further research on site-specific vegetation establishment periods, climate-adapted biomass values and practical feasibility could further expand knowledge in this field.