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Housing aims to provide society with comfortable, healthy living spaces and its built form ultimately shapes the built environment. Consequently, its design, operation, and interactions with infrastructure systems are a powerful determinant of environmental, economic, and social impacts. This paper highlights the importance of assessing housing built forms by answering ten critical research questions. Throughout this paper, we refer to housing built form as the physical properties (e.g., residential density, floor area ratio) of residential buildings and their interactions with adjoining properties (e.g., setback, shading). In Q1 and Q2, we summarize the planning policies that led to current built forms associated with housing and their sustainability impacts, with specific focus on North America and some countries in Australasia. Q3 describes the adverse sustainability impacts of detached single-family houses, while Q4 examines future economic, demographic, and climatic changes that will warrant rethinking housing built form. Q5 summarizes the methods to assess the environmental, economic, and social impacts of housing built form. In Q6 and Q7, we discuss various system boundaries and functional units that are considered for housing life cycle assessment. Q8 and Q9 describe the temporal uncertainty and contextual circumstances underlying housing projects that need to be considered in life cycle assessments. Lastly, Q10 provides a summary of future policy directions to promote housing with lower environmental impact. This paper supports decision-making around meeting housing targets without compromising the environment. • Ten relevant questions on housing built form considering planning policies and impact assessment tools are posed. • Housing built forms are determinant of environmental, economic, and social impacts. • Past, present, and future housing built forms are reviewed. • Life cycle assessment is a useful tool for analyzing the environmental impact housing built form. • Planning policies to support and increase competitiveness of low impact housing built form are provided. [ABSTRACT FROM AUTHOR]

There is general agreement on the importance of green roofs as ways of reducing GHG emissions, reducing overall costs and improving sustainability in urban areas. This systematic literature review highlights life cycle sustainability assessment as an essential criterion to evaluate green roofs. A bibliometric analysis was used to quantitatively review relevant literature. The Scopus database was chosen as a bibliographic database of academic publications. Thes period of search started from 2003 and final search was conducted on February 15, 2023. Based on further in-depth reading, 88 publication records which met the selection criteria, including 74 papers and 14 conference papers. Researchers from the United States contributed almost 31 % of the documents. We evaluated leading studies in this field and discussed assessment method, system boundaries and research gaps through a critical literature review and a systematic search review. Finally, we propose a framework and identify a gap and future research. The environmental aspect of green roofs have received more attention than economic issues. We found that most economic evaluations of green roofs are limited to their construction stage. As yet there is no comprehensive social study on green roofs. We considered a unified study of the economic, environmental impact and social evaluation of green roofs to be warranted. Additionally, various measurement methods should be used to assess the economic profitability of green roofs over the long term. In summary, this study provides a deeper understanding of the environmental, social, and economic performance of green roofs and identifies research gaps as well as future research directions. [ABSTRACT FROM AUTHOR]

Remountable building elements can be transformed according to our changing requirements, ensuring a long use of materials and buildings. To stimulate the implementation of remountable building elements, their environmental impact can be quantified through life cycle assessment (LCA). For a fair comparison between remountable and non-remountable building elements, transformations must be accounted for in LCAs. Yet, currently this is often not done. The purpose of this paper is to develop easy-to-use formulas to calculate the number of transformations and material replacements for remountable and non-remountable building elements. Different types of transformations are considered and it is analyzed how material replacements interact with transformations of the building element. The research is executed on two types of building elements: space dividing walls in offices and façade systems. The robustness of the developed formulas, further referred to as the simple formulas, is examined by comparing their results to those calculated by detailed formulas used in previous research, which determine the moment of occurrence of transformations and replacements. For each building element, the LCA results calculated by the simple and detailed approach are compared for numerous scenarios. In certain cases, the simple formulas over- or underestimate the number of replacements, but the majority of scenarios show limited differences. Furthermore, both approaches yield the same conclusions in a comparative LCA of the remountable and non-remountable space dividing wall. The simple formulas demonstrate how the calculation methods of LCA tools used in practice could be adapted to include the evaluation of remountable building elements. • LCAs of remountable building elements must model multiple cycles (transformations). • Formulas on the number of transformations and material replacements are defined. • Complex transformations where the type or quantity of materials change are studied. • It is analyzed how material replacements interact with transformations of the element. • The formulas form a good approximation of more detailed formulas of previous research. [ABSTRACT FROM AUTHOR]

The competition for limited urban spaces due to the growing demand for both living space and green areas causes conflicts in urban development. This paper aims to provide urban planners with a systematic multi-criteria decision making process and a supporting tool-chain. The process uses multi-objective optimization (MOO) to quantify trade-offs, allowing planners to gain a broad perspective on optimal solutions. The generic process builds an urban simulation model, applies MOO, explores the results in terms of multi-criteria trade-offs, and guides the decision making of urban planners. To enable this process, we present a tool-chain for applying a Gaussian Process Regression based MOO algorithm to a computationally expensive urban simulation model. The tool-chain allows to identify Pareto-optimal solutions and their properties with reasonable computational effort. A case study model is set up in the Grasshopper environment and couples simulation components for outdoor thermal comfort and Life Cycle Assessment. It allows to identify multi-objective trade-offs for a high-dimensional space of urban configuration degrees of freedom such as outdoor vegetation, photovoltaics, and building characteristics. We compare the workflow results to other MOO algorithms and show how it can support decision making in urban planning at early design phases. In our case study, the tool chain was able to investigate the multi dimensional space of urban configurations. It systematically identified Pareto-optimal solutions therein and reduced the number of model evaluations significantly. The case study results showcase the trade-off between lifecycle-based global warming potential (GWP) and outdoor thermal comfort. We identified the number of trees and the coverage of the east and west façades with photovoltaics as the most important parameters. The proposed process proves to be a powerful multi-criteria decision support tool for urban planners. It allows to identify and quantify the Pareto Front of competing urban target trade-offs at early design phases. Additionally, it visualizes them according to the boundary conditions of urban development. The input configurations of the obtained Pareto-solutions serve as a base of urban planning recommendations. In our case study, trees and photovoltaics prove to be good levers in the area of GWP optimal solutions. However, urban planners need to carefully coordinate inputs when aiming for a specific trade-off balance. The tool-chain and the simulation model offer further potential for investigating neighborhood typologies. Thereby, applicants can derive scalable guidance to support the sustainable transformation of the urban environment. [Display omitted] • Structured process to explore the space of Pareto-optimal solutions in urban systems • Surrogate models allow to derive a continuous Pareto Front for decision making • First use of the Paref MOO algorithms in a computationally expensive urban simulation • Trade-off between lifecycle-based GWP and outdoor thermal comfort is quantified • Urban trees and building photovoltaics are important to steer this trade-off [ABSTRACT FROM AUTHOR]

The 2050 decarbonization goals coupled with the growing housing shortage in Europe intensify the pressure on new-build dwellings to enhance their energy performance. Beyond a zero operational energy, the focus has shifted towards reducing embodied carbon (EC). Against this backdrop, this study investigates the simultaneous impact of downsizing and the use of timber in new-build dwellings, EC reduction strategies seldom explored concurrently. Through partial life cycle assessments, three scenarios are modelled: the Small, Medium, and Large House, with two construction variations for each, comparing a modular timber design to a conventional concrete alternative. Designs are based on dwellings built in Almere, the Netherlands. Data is extracted from the Swiss Ecoinvent database using the TOTEM tool and the static −1/+1 approach for biogenic carbon accounting is adopted. Results show a total EC ranging from 42,608 to 70,384 kgCO 2 eq for the timber designs versus 54,681 to 91,270 kgCO 2 eq for their concrete counterparts. Findings suggest that the relationship between house size and EC is sublinear whereby a house twice the size entails less than twice the EC emissions. Only the simultaneous implementation of downsizing and the use of timber achieved 53% carbon savings. The discussion explores implications of outcomes across academic, industry and policy perspectives, challenges in implementing smaller timber dwellings, and study limitations and future research. Beyond its empirical contribution, this paper offers a practical contribution with its hierarchical data analysis approach covering building, element and component. This approach can be implemented by researchers and practitioners alike to inform their design process. • Downsizing and timber are assessed in tandem as embodied carbon reduction strategies. • The embodied carbon of actual European housing scenarios is investigated. • A proposed hierarchical approach decomposes the house into elements and components. • The hierarchical analysis links architectural design choices to embodied carbon. • A small timber house consumes half the embodied carbon of a large concrete house. [ABSTRACT FROM AUTHOR]

Concepts for setting carrying capacity-based benchmarking of life-cycle environmental impacts is an ongoing field of research with an emerging industrial uptake in the built environment. This paper is a critical review of this development compiled in the form of 10 questions that discusses issues and challenges related to definitions, methodology, terminology, and uncertainties. The intention is not to discourage the development but to highlight the need for ensuring consensus and alignment on the aforementioned issues both within the research community and when implementing concepts in practice. Concluding that AESA (Absolute Environmental Sustainability Assessment) aims to address the environmental performance of a service, benchmarked against a functional pollution space, using environmental carrying capacities, rather than comparing it to current 'best practice'. It is crucial to recognize that these carrying capacities are limits, not targets, and whilst allocation of the carrying capacity to services depends on subjective and political decision-making, uncertainties, including subjectivity and emerging scientific data, should be included and communicated clearly in credible AESAs. Collaboration between academia and industry is crucial to align definitions and terminology and avoid misalignments. While AESA lacks a scalable approach for systemic assessments, it serves as a valuable steppingstone for transition, highlighting that achieving a built environment within the currently known functional pollution spaces, requires policy changes and a cultural shift. • Status of research and pitfalls when implementing AESA in the building industry. • Ten questions and answers are posed on AESAs in the Built Environment. • AESA should be based on carrying capacities, defining a functional pollution space. • It is crucial to recognize that carrying capacities are limits, not targets. • Uncertainties should be included and communicated clearly in credible AESAs. [ABSTRACT FROM AUTHOR]

In the last decade, many studies focused on finding optimal design solutions considering trade-offs between different aspects of building design. Accordingly, multi-objective optimization (MOO) approaches have been increasingly applied in the building industry. However, certain aspects must be deepened to ensure a more effective decision-making process in the early planning phase. On the one hand, uncertainties should be considered before making decisions to ensure the robustness of the optimal solutions; on the other hand, decisions are made at different times in building planning, and the sequential order of making decisions should be modeled. This paper presents a holistic two-stage multi-objective stochastic optimization (MOSO)-II framework to minimize the environmental impact of global warming potential (GWP) and cost throughout the entire life cycle of a building (phases of A1-A3, B4, B6 and C3-C4), considering passive and active design strategies in two consecutive stages, under uncertainty. Herein, individual/use and political/market uncertainties are considered. As a proof of concept, the proposed framework is applied in a case study for a generic zone in a multi-family terraced residential building type with solid brick construction. The advantages of the proposed framework are validated by comparing it with alternative single-stage MOSO frameworks. Results show that the proposed two-stage MOSO-II framework can deliver a smaller range of solutions with a better performance in terms of lower GWP and cost. It indicates that the proposed framework can effectively assist planners in decision-making by reducing the effort in choosing the proper solution. Secondly, the results also emphasize the importance of passive design strategies in sustainable building planning. In addition, the energy mix structure and cost of energy sources should be carefully adjusted in the future to promote a more ecologically sustainable building design. • A two-stage multi-objective stochastic optimization framework for building design. • Passive and active design strategies as two decision stages in building planning. • Targeting at minimum global warming potential and cost in the optimization problem. • Integration of uncertainties in the decision-making process for early design phases. [ABSTRACT FROM AUTHOR]

When calculating buildings' environmental impact through life cycle assessment (LCA), simplifications in the life cycle inventory phase of technical installations are common. Often authors argue that these simplifications are essential to minimize time and effort. However, it is unclear to what extent these simplifications are justified. The challenge lies in establishing simplified models that do not compromise the robustness of results, which first requires detailed LCAs. Therefore, this paper aims to acquire knowledge about (1) the significance of individual components in heating and ventilation systems' design, (2) the relative contribution of technical installations to embodied and life cycle impacts at building level, and (3) the difference between a detailed and simplified approach to derive guidelines for simplified calculations. In this research, a Flemish single-family dwelling is adopted as reference building, including six heating and four ventilation scenarios. Firstly, the current state-of-the-art in research on the environmental impact of technical installations is outlined. Secondly, an extensive data inventory is performed, suggesting different approaches to address data limitations. Finally, the environmental impact is calculated over a 60-year study period, following a cradle-to-grave methodology. The results show that a simplified approach, considering only generation systems, underestimates embodied and life cycle impacts by 8–12 % and 4–6%, respectively. Technical installations contribute 12–33 % to the embodied impacts of the new build dwelling, whereas in the context of the overall life cycle impact, technical installations contribute 5–20 %. Moreover, the study highlights the environmental significance of individual heating and ventilation components beyond generation systems. • The importance of technical installations in whole-building LCA is studied. • Detailed LCA of heating and ventilation systems in a single-family dwelling. • Technical installations contribute up to 33 % and 20 % to embodied and life cycle impacts. • The study shows the HVAC components' significance beyond generation systems. • A simplified approach underestimates embodied and life cycle impacts up to 12 % and 6 %. [ABSTRACT FROM AUTHOR]