• Energy Research

What is embodied carbon and why is it a significant challenge for clients and designers in the real estate and construction sector? It is the sum of greenhouse gas (GHG) emissions that arise in the life cycle of a building during manufacture and construction (upfront), maintenance and replacement of building components (recurrent), as well as dismantling and waste processing (end of life). Currently, the relative and absolute share of embodied carbon in the life cycle of a single building is growing and becoming a dominant factor in the case of energy-efficient buildings. For example, for new buildings, it can represent more than 50% of life-cycle carbon. Against this background, embodied carbon is becoming an object of assessment not just in research but also in design and decision-making. It also becomes a key action to reduce GHG emissions. Embodied carbon assessment and reduction are being increasingly mandated in national regulations. Clients and designers (as key actors in the supply chain) can harness new knowledge and tools to reduce embodied carbon as part of a strategy to reduce overall GHG emissions. Appropriate methods, data, benchmarks and tools are being further developed and operationalised to support the processes for specifying and designing low carbon buildings. An overview is presented of the state of knowledge and current developments. Constructive recommendations are provided for actions that clients and designers can take. 'Key findings' From the perspective of a single building’s life cycle, the proportion of embodied carbon is around 50% on average for new energy-efficient buildings. From a macro-economic perspective, approximately 10% of global energy-related CO2 emissions are attributable to the embodied emissions of buildings. Designers can influence and assess embodied carbon according to related design targets in the client’s brief and/or legal requirements. A trade-off between operational and embodied carbon is typical, but possibilities exist to optimise both sides. Embodied carbon can be reduced by selecting low carbon construction products and/or reused building components. Further possibilities are the revitalisation of existing buildings, the extension of their service life, the minimisation of useable areas (sufficiency), as well as the optimisation of buildings and their components. With good design, it is possible to construct low embodied carbon buildings with little or no additional costs, and even generate economic benefits.

Target values for creating carbon budgets for buildings are important for developing climate-neutral building stocks. A lack of clarity currently exists for defining carbon budgets for buildings and what constitutes a unit of assessment—particularly the distinction between production- and consumption-based accounting. These different perspectives on the system and the function that is assessed hinder a clear and commonly agreed definition of ‘carbon budgets’ for building construction and operation. This paper explores the processes for establishing a carbon budget for residential and non-residential buildings. A detailed review of current approaches to budget allocation is presented. The temporal and spatial scales of evaluation are considered as well as the distribution rules for sharing the budget between parties or activities. This analysis highlights the crucial need to define the temporal scale, the roles of buildings as physical artefacts and their economic activities. A framework is proposed to accommodate these different perspectives and spatio-temporal scales towards harmonised and comparable cross-sectoral budget definitions. Buildings & Cities, 1 (S 1) ISSN:2632-6655

In order to be able to quantify, evaluate and specifically reduce environmental impacts caused by buildings, suitable assessment methods and design tools are needed. Such methods and tools enable decision-makers not only to recognise but also to influence the impacts on the environment as early as the design stage as well as throughout the project. The further development of such assessment methods and design aids for buildings was one of the tasks of the IEA EBC Annex 72. The basic principles and recommendations for action developed by more than 60 scientists from 25 countries in Europe, the Americas and Asia are now available and presented in this report.

Applied Energy, 258 ISSN:0306-2619 ISSN:1872-9118

Densely built-up areas are challenged by reduced biodiversity, high volumes of runoff water, reduced evaporation, and heat accumulation. Such phenomena are associated with imperviousness and low, unsustainable utilisation of land and exterior building surfaces. Local authorities have multiple objectives when (re-)developing future-proof districts. Hence, exploiting local potentials to mitigate adverse anthropogenic effects and managing the resource of urban land/surfaces have become key priorities. Accordingly, a five-level hierarchy for a land-sensitive urban development strategy was derived. To support the operationalisation of the hierarchy, we present the model Namares, a highly resolved GIS-based approach to enable spatially explicit identification and techno-economic and environmental assessment of intervention measures for advantageous utilisation of available surfaces per land parcel. It uses existing data and covers the management of economic, natural, and technical resources. Nine intervention measures are implemented to identify potentials, estimate investments and annual costs, and assess the appeal of existing subsidies. The approach was applied to a case study redevelopment area in a large city in Germany. The results provide spatially explicit information on greening potentials, estimated investments, subsidy demand, and other quantified benefits. The case study results show the limited potential for additional unsealing of impervious surfaces by transforming ca. 10% of sealed ground surface area into new urban gardens. At the same time, up to 47% of roof and 30% of facade surfaces could be utilised for greening and energy harvesting. The approach enables a comprehensive localisation and quantitative assessment of intervention potentials to enhance decision support in land-sensitive urban development strategies.

Several different definitions of ���net-zero��� or ���climate-neutral��� buildings have arisen and are causing confusion. Different approaches quantify the greenhouse gas (GHG) emissions of buildings over their life-cycle. A typology is proposed based on distinctions between absolute and net-zero-emission buildings in relation to operational and full life-cycle approaches. Besides the absolute zero-emission approach, three different net-zero-emission approaches are: (1) a net-balance approach, which includes credits caused by potentially avoided emissions beyond the system boundary provided by exported energy; (2) an offsetting approach, based on the purchase of CO2 certificates; and (3) a technical approach, based on negative-emission technologies. The declaration of the approach chosen will provide clarity when discussing (net/absolute)-zero emission or climate-neutral buildings.