While the operational energy use of buildings is often regulated in current energy saving policies, their embodied greenhouse gas emissions still have a considerable mitigation potential. The study aims at developing a multi-objective optimization method for design and renovation of buildings incorporating the operational and embodied energy demands, global warming potential, and costs as objective functions. The optimization method was tested on the renovation of an apartment building in Denmark, mainly focusing envelope improvements as roof and exterior wall insulation and windows. Cellulose insulation has been the predominant result, together with fiber cement or aluminum-based cladding and 2-layered glazing. The annual energy demand has been reduced from 166.4 to a range between 76.5 and 83.7 kWh/(m2 y) in the optimal solutions. The fact that the legal requirements of 70 kWh/(m2 y) are nearly met without building service improvements indicates that energy requirements can be fulfilled without compromising greenhouse gas emissions and cost. Since the method relies on standard national performance reporting tools, the authors believe that this study is a preliminary step towards more cost-efficient and low-carbon building renovations by utilizing multi-optimization techniques.

Introduction: Buildings are responsible for 39 % of CO2 emissions in the world and have the largest consumption of natural resources. The concept of Circular Economy can be used as an approach for mitigating environmental impact in this sector. Circular economy in the built environment can be implemented on a building level through preservation instead of demolition and new construction. In order to assess the environmental impact, the Life Cycle Assessment (LCA) framework can be used. The purpose of this study is to expand the existing building-LCA framework from the CEN TC 350 standards to include existing buildings on the building site in the assessment of buildings and demonstrate the framework on a building case. This is done in order to include the environmental benefits from preserving the building materials that already exists on the building site. Methods: The framework is developed based on the existing standard for LCA for buildings and the framework is demonstrated on an existing school building. Results: The study develops and demonstrates a framework for performing LCA on buildings when an existing building is the starting point. The framework includes scenarios for 1) preservation, 2) renovation and 3) demolition and new construction. The case building shows the importance of including demolition of the existing building as it accounts for 12 % of impacts. It furthermore illustrates how the scenarios can be compared, especially in terms of when the impacts occur, i.e. that most impacts from scenario 3) happen today, which can be a challenge with a limited climate budget. Conclusion: The developed framework allow us to broaden the LCA scope to include existing buildings in the assessment such as demolition of existing buildings on building site. This makes it possible to evaluate the circular strategies on building level using LCA to the benefit of building designers, clients and policy makers.

Buildings are a major cause of global resource consumption, greenhouse gas (GHG) emissions and other impacts on the environment, originating from both operational energy and material use. Informed design decisions can help mitigate potential impacts on the environment, by the use of life cycle assessment (LCA) in the early project stages. In order to mitigate building environment impacts throughout the industry, architects and engineers need tools that are integrated in the design workflow and based on the information available. Existing LCA tools for building design professionals are predominantly embedded in a specific context such as a country or a sustainability scheme. This paper provides learnings for the development of context-tailored tools for building-LCA using the case of Denmark, with specific focus on GHG-emissions that are in focus worldwide. Based on stakeholder involvement, four key areas were defined: Default information, flexibility, environmental design feedback and transparent results. Tool functions include a component library and a quantity estimator for bridging incomplete building information. A comparison monitor displays the performance of design solutions selected in the model, while a number of graphs and tables provide analysis of inventory and results. Finally, a customisable model data export, a complete input/output file for revision and custom analysis are among key functions for transparency.

The concept of circular economy has been introduced as a strategy to reduce the greenhouse gas (GHG) emissions from buildings and mitigate climate change. Although many innovative circular solutions exist, the business model is challenged by a lack of environmental data on the circular solutions, and thus the potential benefits are not verifiable. The study assesses the embodied GHG emissions of five circular building elements/components. Circular solutions are compared with conventional solutions to ascertain whether the business model has the potential to reduce GHG emissions. The GHG emissions are quantified using life-cycle assessment (LCA) for five circulareconomy and three conventional building elements/components. The environmental data show that circular building components have the potential to reduce GHG emissions. However, there is a risk of increasing the GHG emissions when compared with conventional solutions, emphasising the need for standardised environmental data. Lastly, the study identifies logistic, economic, technological and regulatory barriers that prevent complete implementation of circular economy. Practice relevance Standardised environmental data on building elements/components are needed to support decisionmaking at local and national levels. Uncertainties about waste from manufacture and transport in the production stage can affect the environmental potential to such an extent that the benefits from introducing circular economy are lost. One central barrier is identified that prevents complete implementation of the circular economy in buildings; the industry is not geared to support a steady supply of some circular building elements/components. In general, it is clear that the implementation of circular economy requires the identification of environmental, logistical, economic, technological and regulatory concerns.

There is an increasing demand for Life Cycle Assessment (LCA) as a method for environmental impact and resource assessments of buildings. At early design stages, where major design decisions are made, the potential for improving the environmental performance using LCA is greatest. However, detailed building information is usually not available at this time. This paper presents the recent extension of LCAbyg, the official Danish building LCA-tool, integrating an LCA approach for situations, where building design and material choices are not yet fully determined. The tool assists the user in establishing a complete building inventory by providing a default component library including building services and a guide for estimating quantities. Default components in the library are based on the integrated product database Ökobaudat. A convenient generation and comparison of variants improves usability, while a new LCA design guide shall increase the uptake of LCA in larger parts of the building industry. The methodological choices of the approach are laid out and discussed. The presented approach is not limited for use in early stages, but may improve feasibility in building LCA in general as default and estimated values may be refined towards more detail in later stages of the project.