Reusing the building elements is the highest possible level of circularity for buildings that must be demolished, potentially slowing down climate change. This study explores the embodied carbon reduction of construction of a pilot building with structural elements of reused concrete. The assessment focuses on applying different methodological approaches and discussing the upscaling opportunities of reusing concrete elements from a global warming potential perspective. The assessment shows large embodied carbon savings compared to conventional building practices like recycling the concrete and building with new low-carbon and prefabricated elements. Embodied carbon saving is also obvious when applying alternative system modelling, future market projection and different allocation approaches of the production emissions of the elements. Finally, the study emphasises the need for further research in evaluating the benefits of reusing structural concrete elements broadly, like including the deconstruction impact related to elements for reuse, to be able to draw general conclusions.

Circular Economy has been highlighted internationally as a solution to mitigate global warming. This study examines the reuse potential of precast concrete elements in Swedish residential buildings, quantifying its impact on element flows and stock using life cycle assessment. While reuse achieves higher carbon savings than recycling, the overall impact remains modest due to limited demolition and high demand for new materials, with most precast concrete elements still embedded in the stock. Assuming all deconstructed elements are reused, savings reach up to 1 % of lifecycle emissions, with a proportional relationship observed between reuse share and embodied carbon savings. Despite aligning with IPCC recommendations for increased prefabrication, the growing precast concrete intensity in buildings with precast concrete structure reflects rising resource consumption. Further studies should assess how technological advancements affect life cycle impacts and reuse feasibility, while also exploring reuse in non-residential buildings and policy measures to strengthen circular economy strategies.

Concrete is the most used construction material, accounting for 8% of global CO₂ emissions. Various strategies aim to reduce concrete's embodied carbon, such as using supplementary cementitious materials, utilizing cleaner energy, and carbonation. However, a large potential lies in reusing concrete for new buildings in a Circular Economy, thereby closing material loops and avoiding CO₂ emissions.

This study focuses on the reuse of precast concrete elements. We present a digital workflow for assessing reuse by predicting the remaining service life, estimating CO₂ uptake by natural carbonation, and calculating the embodied carbon savings of concrete reuse. Both carbonation rates from EN 16757 and our investigation were applied to a case study building.

While EN 16757 rates suggest that most precast elements have reached the end of their service life, our assessment shows that these elements have a sufficient lifespan for reuse. Plaster and coverings significantly delay carbonation and extend service life. During the first service life following EN 16757, carbonation was 19,2 kg CO₂/m³, whereas our prediction was 5,4 kg CO₂/m³. Moreover, CO₂ uptake during service life, including reuse, was less than 6% of the embodied carbon. The climate benefits of reuse greatly exceeded those of carbonation.

Furthermore, carbonation did not have a decisive influence when applying Cut-Off, Distributed, and End-of-Life allocations for assessing embodied carbon of re-used elements in subsequent life cycles. The digital workflow is useful in quickly assessing lifespan, carbonation, and embodied carbon of concrete. It can be leveraged as a decision-making tool when designing for reuse.

Concrete production contributes to around 8-9% of global CO₂ emissions. Reusing building components in a circular economy can contribute to closing material loops and lowering CO₂ emissions. When reusing concrete elements, it is necessary to have effective methods for evaluating their reuse potential. In this study, a novel digital workflow is developed to support the reuse of precast concrete elements by evaluating their lifespan based on carbonation depth. The workflow relies on automated retrieval of material quantities and information from a digital model. This model is then coupled with environmental data on construction products and calculation methods for CO₂ uptake in concrete by carbonation. The remaining service life of concrete elements was calculated for a case study. For reference, CO₂ uptake during the first service life was estimated at 4973 kg CO₂ or 4% of the embodied carbon. Hence, the potential benefits of reuse outweigh those of carbonation. The presented approach supports the decision-making process when evaluating the reuse potential for concrete elements. The digital workflow can help designers make quick decisions concerning the lifespan and carbon footprint of concrete. The digital tool can be extended in future work with more parameters to evaluate additional sustainability indicators.

Rapidly reducing the climate impacts of the construction and use of buildings is acknowledged as a key lever to meet European and national climate goals. Life cycle-based regulations, in the form of mandatory declaration of the climate impact of new-build, are being introduced, often planned to be or already complemented with performance-based limit values. This development has increasingly raised questions on how different system boundaries for similar limit values applied in various countries might lead to diverging implications in practice. A sample of 50 real-life case buildings of different typologies, representative of contemporary Swedish construction, is used to compare implications of two different system boundaries for embodied GHGe assessment: SB1) life cycle modules A1-A5 i.e. initial, that is upfront GHGe and SB2) life cycle modules A1-A5 + B2–B4, i.e. adding recurring GHGe, according to the European EN 15978 standard. The results show that for the two system boundaries applied, no difference is seen concerning the sample buildings' ability to perform below a limit value as defined in current Swedish regulatory plans, nor would it lead to different design choices to ensure that a building performs below the limit value. The results of sensitivity analyses along with the relative nature of the results, suggest these conclusions are also relevant for other regulatory contexts. As a conclusion, this study shows that implementing LCA-based regulations focusing on initial embodied GHGe is an important step to rapidly and effectively address GHGe associated with new-build.

Initiatives on operational carbon have been an integrated part of legislation in many countries for decades, but the issue of embodied carbon is just starting its breakthrough in a regulatory context. This chapter provides an account of how the introduction of LCA-based limit values for whole-life-carbon has been approached in Finland, Sweden and Denmark. The starting point for these whole-life-carbon declarations have been the policies outlined via national climate acts, and there has been extensive knowledge exchange between the three neighbouring countries. Still, the LCA-based assessment methods outlined for the regulation have taken significantly different paths. For instance, the Swedish approach focuses on the upfront carbon from production and construction processes, whereas the other two approaches include the use- and the end-of-life stages. The methodological variations reflect the different national weightings between the ease-of-application for users and the accuracy- to-scope of the building model and its real life-cycle impact. All three approaches have drawn up reference values for typical buildings, and have already, or are planning to, introduce politically defined limit values for new buildings. At the same time, distributions from a global carbon budget approach show large discrepancies between the emsissions ‘allowed’ for new constructions (<2 kg CO2e/m2/year) and the limit- and reference values in place for the countries (around 9-15 kg CO2e/m2/year). This makes it clear that additional giant leaps are needed for policies in the building industry to operate within the planetary boundaries.

In light of the climate crisis and conflicting political ambitions in many countries to rapidly increase the number of dwellings, what housing strategies could reduce emissions? Co-living is one strategy sometimes highlighted but rarely implemented in mainstream construction practices. Using two Swedish case studies, the potential embodied carbon savings are explored for co-living designs. When comparing building designs, normalisation of impacts or energy use per floor area is unequivocally the norm. The present comparison between co-living and traditional apartment design indicates an embodied carbon savings at the building level of 10–20% depending on whether embodied carbon is normalised per gross or residential floor area. However, normalisation per capita (inhabitant) shows substantially higher savings of 21–36% depending on the case studied. The effect of different metrics is illustrated to quantify potential embodied carbon savings of non-mainstream building design solutions such as co-living. Even more substantial embodied carbon savings can be achieved by avoiding new construction through the ability of enabling a more efficient use of indoor space. The need for rethinking carbon and space metrics will help the building sector meet emission targets. PRACTICE RELEVANCE Evidence is provided to show that design for co-living could be one way to offer a climate-efficient and qualitative housing alternative for single households in many countries. However, to visualise such potentials, developers are recommended to use additional metrics when evaluating how resource or climate-efficient are alternative designs. Traditional metrics such as kWh or kg CO2 e/m2 of gross or heated floor area ought to be complemented by displaying resource use or embodied carbon per designed number of building user and per accessible floor area for each user. Up-to-date generic values are provided for the embodied carbon of different types of space. These can be used in early planning to display the consequences of the number of kitchens and bathrooms and their space occupation in client decisions and early architectural design.