LCM at the Urban Scale: BIM and Nature Based Solutions

An assessment of energy and environmental performances of building stocks at large spatial scales is increasingly needed for decision support in sustainable urban planning and policy making. While current bottom-up building stock models have mainly focused on the operational energy use up to the last decade, a more holistic environmental assessment of the different stages of buildings life cycle is now required. However, extending a Life Cycle Assessment (LCA) model from the building to the district or city scales entails a number of methodological and operational challenges.

LCA as inventory and environmental impact assessment tool can largely benefit from datasets and knowledge base frameworks based on Building Information Modelling (BIM) and Nature-Based Solutions (NBS). The use of BIM has the aim to help engineers to design digital models and share building information in an interoperable and reusable way [1]. However, firstly to apply BIM concepts designers create 3D models of buildings hinging upon built-in databases, which are not interoperable with the analysis tools used in LCAs of buildings. This hampers the quantification of the potential environmental impacts of buildings using those materials databases to support the decision-making process [2, 3]. Secondly, the modelling of a detailed BIM is time-consuming and especially in early design phases detailed information is usually not yet available. To this end, basic 3D models can be used to do simplified LCAs of buildings and neighbourhoods and compare variants in early design, when the optimization potential is high. Thirdly, a number of standards and data formats for 3D modelling and visualization of buildings and cities have been developed, e.g. CityGML [4, 5]; however, these models are often not used in planning and operation, partly because of problems with interoperability and partly due to the efforts to keep the models up to date [6].

Finally, BIM-based sustainability in the construction sector relates, at higher scales than single buildings, with the sustainability of urban planning and management, and therefore to the efficient use of resources and impact mitigation measures in cities. In this regard, it is worth observing that the improvement of cities’ sustainability is nowadays supported through the explicit implementation of Nature-based Solutions (NBS) [7, 8] in urban planning. Those represent, among others, a means to activate impact mitigation measures in cities [7, 9]. How to harness NBS to promote well-being in urban areas does represent another challenging and timely research theme [10, 11], which is not explored in the LCA context. NBS strictly belong to the sustainable management of natural resources, urban spaces and technological know-how. Their introduction in urban contexts (at the spatial level of building, neighbourhood, or whole city) is recommended for several reasons, such as to reinforce the social cohesion and reduce poverty, and enhance the provision of urban ecosystem services and biodiversity. However, the impact of NBS projects, in terms of benefits, co-benefits and costs is still not sufficiently understood. Hence, the study of NBS related impacts, based on an LCA approach, could facilitate the interpretation of the sustainability dimensions underpinning NBS.

This LCM2017 conference session explored the challenges mentioned above via some case studies, proofs of concept and a discussion based on different experts’ visions. The objective was to offer an overview on some methodological and applied advances that, from building to city scales, may open up concrete opportunities for: (i) a better exploitation of urban resources, data and know-how (i.e. integration between BIM and LCA), and (ii) a smooth transition towards sustainable and resilient cities (i.e. assessment/implementation planning of NBS with a life cycle thinking approach).

The case study discussed by Alexander Borg has shown how the use of an external tool, like Excel, as an intermediate step for inventory modelling is very time consuming and not optimal to ensure a convenient use of a BIM-LCA model. There is potential for automation of this process, but it is important to first being able to ensure the reliability and transparency of the data used in an automatic data transfer process. The automation of information transfer from external data sources to BIM is one of the current challenges that BIM-LCA integration has to face.

Ongoing research shows that ventilation systems can contribute significantly to increase GHGs emissions, especially considering that these systems do not always work properly from the start, and faulty equipment must be replaced, thus generating additional emissions through materials and labour. The presentation showed that, given the role they play in buildings performances, embodied impacts of ventilation systems should be reduced, via increased recycled and recyclable materials content, and taking into account also alternative ventilation methods like hybrid natural ventilation.

The “early BIM” approach presented by Alexander Hollberg raised a lot of interest in the audience. A question was asked about the comparison between the impacts of a building where environmentally sound decisions are taken at the early stage and one where these decisions are taken only at later stages of the design. The comparison has not been done so far by the authors, but the same systems boundaries were used in the early stages as they would apply to later stages. As pointed out by one of the attendees, the approach presented is similar to the one taken by other tools used for LCA in building design, especially Tally^TM. However, as Alexander Hollberg highlighted, the main difference lays in the full integration into the design process. Their approach provides instant feedback while changing parameters, which is a unique feature in the current state of the art. Furthermore, they combine operational energy demand calculation and the embodied impact calculation in one method. This kind of approach appeared slightly different from a “conventional” BIM approach. The authors call it “early BIM”, because they link information to the geometric 3D model. Conventional BIM, such as Revit models, contain more detailed information stored in the 3D model. This results in a more complex model which cannot be adapted as quickly as simple 3D models. Therefore, they use the simple models in early stages, which can then ideally be enriched with detailed information throughout the design process.

The topics discussed by Adélaïde Mailhac gave an interesting overview of the potential of BIM use in an LCA framework, explaining that BIM can be used in every phase of the LCA, not just in the early conception stage. However, data availability in the right format (e.g. CityGML compliant data) still remains a problem, since data is not provided easily by every actor, public or private.

Finally, the approach presented by Özge Yılmaz intrigued the audience due to its modular structure, which integrates different approaches. It also raised concerns about the seamless incorporation of ABM, which is a dynamic simulation tool, with a rather static LCA approach. The presenter recognized that LCA provides a snap-shot of environmental impacts over a given period of time and a shift from static LCA to more dynamic LCA is certainly necessary for successful integration of ABM and LCA. A second observation concerned the suggestion to include not only the behavioural patterns, but also consumption patterns in the ABM simulations. This aspect will be taken into account in conjunction with an urban metabolism approach within the Nature4Cities project.

Another question was asked about the actual sustainability assessment of NBS. In other words, NBS are nowadays often sought because they are capable of improving a certain element of an urban system, improve its performances with respect to a specific aspect (e.g. green facades to improve the thermal comfort in buildings and reduce heating and cooling loads) or supposedly increase people well-being. But is the lifecycle sustainability of NBS systematically assessed? Are we ready to provide holistic assessments of NBS, or are we rather running the risk of swooping on NBS without evaluating any possible side effect? The answer to this question can be found in the consistent application of holistic (lifecycle based) assessment of NBS, as proposed in Nature4Cities.