Authors

Marco Capelli (a), Andrea Botti (b), Remo Fabrizi (c), Simone Marino (d), Francesco Conserva (e)  (abcde are superscript)
a Marco Capelli, Facade Engineer, BECxA, LEED AP BD+C, Open Project
b Andrea Botti, Head of Sustainability, Open Project
c Remo Fabrizi, LEED GA, Open Project
d Simone Marino, BIM and Sustainability Specialist, Open Project
e Francesco Conserva, Vice President, Open Project

Author contributions

Marco Capelli developed the research concept and scope, supervised the LCA model development, discussed the results and wrote the conclusions of the article.
Andrea Botti helped organising the structure of the article, produced the graphics, wrote the introduction and contributed to conclusions and limitations.
Remo Fabrizi and Simone Marino built the LCA models using the OneClickLCA software package.
Francesco Conserva authorized the use of confidential documentation for the purpose of the research.

Introduction

The importance of addressing embodied and whole-life carbon

The built environment is responsible for approximately 39% of the global Greenhouse Gas Emissions (GHG) : 28% from operational emissions (i.e. those resulting from energy consumption needed to heat, cool and power buildings), and 11% from embodied carbon emissions, that is those associated with the extraction, production, transportation, and assembly of building materials, as well as their end-of-life disposal [2].

In the face of escalating climate change concerns, associated both with the impacts currently observed globally and the alarming IPCC projections for the medium and long-term future, the construction sector has been increasingly recognising the fundamental importance of addressing embodied carbon emissions with urgency. As a matter of fact, while operational energy and carbon have been received attention over the last two decades, the substantial role of embodied carbon has been recognised in the recent years.

At a European level, this is reflected in the EU Taxonomy regulation [3], a classification system aimed at promoting sustainable activities and transforming investment practices and reporting related to sustainability. The EU Taxonomy, enforced through the legally binding EU Regulation 2020/852 since 2021, plays a vital role in supporting the EU's ambitious target of achieving climate neutrality by 2050.

In accordance with the regulation, any building larger than 5,000m2 is required to undergo a Life Cycle Assessment (LCA) analysis following the methodology outlined in EN 15978:2011. This analysis examines the Global Warming Potential (GWP) resulting from all stages of the building's life cycle, including construction, usage, and end-of-life. The LCA report should be readily available to investors and clients upon request, facilitating informed decision-making. However, it is worth noting that the regulation does not specify any quantitative goals, leaving room for industry stakeholders to proactively strive for carbon reduction targets.

Emerging embodied and whole-life carbon benchmarks: RICS and LETI (UK), AIA and CLF (US)

The definition of appropriate benchmarks is a necessary step towards the creation of a consistent and transparent method to measure building performance, most importantly with the goal to minimise resource use, decarbonise and reduce the overall environmental impact of the Architecture, Engineering and Construction (AEC) sector. This is now well-established when it comes to energy efficiency and operational energy (and carbon) where following the introduction of the EPBD, the introduction of Energy Performance Certificates (EPCs), now mandatory for any building to be sold or rented out, has been a crucial step towards achieving the goal. Leading global initiatives within the AEC sector are aiming at somehow similar goals, that is to reach the definition of robust benchmarks that allow to rate buildings’ performance based on their embodied carbon.

The Royal Institute of Chartered Surveyors (RICS) in the UK launched an Embodied Carbon Database designed to help built environment professionals identify where carbon reductions can be made throughout the construction process of buildings. The database indicates the typical embodied carbon footprint of different building typologies and for each phase of construction.

The London Energy Transformation Initiative (LETI) has been working on aligning definitions, scopes, measurement methodologies, and targets for embodied and whole life carbon following the release of the Embodied Carbon Primer in 2020. LETI has developed an embodied carbon rating system to track the necessary performance improvements from now until 2030. They also provide a self-certifying Embodied Carbon Reporting Template, where project owners can place their projects against the LETI benchmarks for an indicative rating.

In the U.S., the American Institute of Architects (AIA) and the Carbon Leadership Forum (CLF) have placed great focus on reducing embodied carbon associated with buildings. The AIA-CLF Embodied Carbon Toolkit for Architects provides an understanding of measuring embodied carbon through the methodology of a life cycle assessment and equips designers with strategies to reduce embodied carbon in their projects.

Being aware of the contribution from buildings to global carbon emissions throughout their lifecycle, at Open Project we have been carrying out Embodied and Whole Life Carbon analysis on all our projects.

The research examined four buildings, three of which have been built, whereas the fourth one is undergoing technical design stage. A detailed calculation of the CO2 emissions related to the construction stage has been undertaken and the results can be compared with the figures from standards and international best practices, such as RICS and LETI in UK, AIA and Carbon Leadership Forum (CLF) in the U.S.

By providing representative case studies, the research here presented seeks to contribute to the definition of a benchmark for the CO2 emissions related to the construction of student housing and hospitality buildings, in a similar way to what has been done as part of best-practice initiatives such as LETI in the UK.

Research objectives

Being aware of the contribution from buildings to global carbon emissions throughout their lifecycle, at Open Project we have been carrying out Embodied and Whole Life Carbon analysis on all our projects.

The research examined four buildings, three of which have been built, whereas the fourth one is undergoing technical design stage. A detailed calculation of the CO2 emissions related to the construction stage has been undertaken and the results can be compared with the figures from standards and international best practices, such as RICS and LETI in UK, AIA and Carbon Leadership Forum (CLF) in the U.S.

By providing representative case studies, the research here presented seeks to contribute to the definition of a benchmark for the CO2 emissions related to the construction of student housing and hospitality buildings, in a similar way to what has been done as part of best-practice initiatives such as LETI in the UK.

Case studies

The Hotel Bologna Fiera project comprises an extension an existing building, with a new 6-storey wing hosting 60 rooms. The intervention also included, for the existing wing: structural work to achieve a seismic improvement of the existing concrete frame structure; a strip out and replacement of the entire building envelope; a substitution of the internal partitions and finishes and a complete replacement of MEP components.

The Social Hub project comprised a complete strip-out of an existing office building, with the demolition of MEP systems, the seismic improvement of the existing concrete structures and the addition of a top floor (steel structure).

Beyoo Laude Living Student Accomodation is a new construction in an infill site situated north of Bologna train station.

Hotel Porta Mascarella is a new building, located in an infill site between existing building to the west, a public road to the south and east, and the railway on the north side.

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Methodology

Scope of the Life Cycle Assessment

​In this research stages A1-A5 (Cradle to Practical Completion) have been considered. These stages, often referred to as “Upfront Embodied Carbon”, are under the control of the design team and the General Contractor and are associated with the vast majority of the total emissions during the entire lifecycle. This is aligned with the afore-mentioned international best-practices, such as RICS and LETI [3].

Software and data sources

The quantities of the structural and architectural materials used have been extracted from bill of quantities calculated for the detailed design stage.
The calculation of GWP associated with stages A1 to A5 have been calculated by using manufacturer-specific Environmental Product Declarations (EPD), that present transparent, verified and comparable information about the life-cycle environmental impact of product. The OneClickLCA software package was used to create a virtual model, allowing to access a large and comprehensive database of EPDs as well as generic country-wide as well as EU-wide product data. It is important to note that a good material and technology expertise should be required to interrogate international databases, such as that provided by OneClickLCA, to perform LCA studies.
This is particularly true for materials like concrete, whose carbon impact – typically the highest among all building materials – can vary greatly depending on factors such as: minimum cement content (kg/m3) for resistance class, mix design (hence optimum cement content) which is usually established during construction, presence of additives or curing time requirement which may derive from off-site manufacturing / prefabrication. All of these factors have a substantial impact on embodied carbon estimates, and it is important to factor in the tolerances associated with estimates produced at the design stage. In that regard, the expertise offered by Open Project’s site supervision team proved essential in order to identify specific range of concrete mix design that actually used in all completed buildings that were analysed.
For two of the projects considered, The Social Hub and Unahotels Bologna Fiera, that were built a few years prior to this study, the authors chose to use ‘common practice’ materials for the purpose of this assessment. This meant utilising higher carbon intensity materials and components, such as for instance the choice of structural steel with much lower recycled content than currently available. This ‘penalisation’ of carbon intensity associated with construction in the past was introduced to account for the progressive decarbonisation of the Italian national grid.
The data has been reported with building components according to the standard EN 15978:2011 and Level(s) European framework for sustainable buildings, as indicated in Table 1.​

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Results and discussion

Results

 Unahotels Bologna Fiera

For the Hotel Bologna Fiera project, aggregated data is here presented, combining carbon associated with both refurbishment of the existing wing and the construction of the new wing. This reflected the fact that the rooms located in the new wing would still be functionally dependent from the common and ancillary areas, located in the existing building.
Presenting embodied carbon data for interventions that seek to add functionality or space, improve performance and extend the longevity of existing buildings by means of re-cladding, refurbishment, extensions, or everything combined is significant for the purpose of research.
The new wing has been built in a small infill site, a very small floor plan in reference to the heigh, and a limited efficiency in the ratio room number / GIA.
The high emissions of the foundation works (90.4 kgCO2e/m2GIA) are due to the piling wall at the perimeter and the jet grouting works. Structures are also carbon intensive (138.7 kgCO2e/m2GIA), due to construction of a new wing and particularly the carbon impact of a new structural bracing system. Building envelope carbon intensity is also high (113.3 kgCO2e/m2GIA) and this is due to the outer aluminium skin, comprising shading lamellae, expanded mesh panels as well as composite aluminium rainscreen panels.

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The Social Hub
No works have been necessary to the existing foundations or the lower ground parking garage structures, and that is reflected in the data presented. A low carbon impact was also reported for the superstructure (kgCO2e/m2GIA) and this due to the fact than new structures were required for the 3rd floor only. Seismic adaptation and improvement to the remaining floors required substantial workmanship but low material usage, hence low embodied carbon.
Originally designed as an industrial facility, the building required significant works on the horizontal partitions in order to achieve a consistent finished floor level and install a raised floor as part of the conversion to office space.
Substantial work was also required on the internal partitions, due to a high floor-to-floor height, notably higher than current practice for hospitality buildings (approx. 5m in lieu of the typical 3.5m).
Facades also presented very low embodied carbon (35 kgCO2e/m2GIA), and this is due to a minimal design that avoided rainscreen or solar shading and consisted mainly of solid walls (drywall system).

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Beyoo Laude Living Student Accomodation
The high CO2 emissions associated with foundation works (150 kgCO2e/m2GIA) derive from new foundation piles as well as provisional retaining wall though piling the site boundary that were necessary to allow excavations.
The emissions associated with the reinforced concrete frame are high (151.8 kgCO2e/m2GIA), despite the use of low embodied carbon cement. This is due to the building height (15 storeys).
The upfront carbon necessary for the facades (53.2 kgCO2e/m2GIA) is fairly low, due to the absence of any rainscreen external cladding. However, the figures are higher than for the previous case study as all windows were equipped with aluminium external blinds.
 

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Hotel Porta Mascarella

The high CO2 emissions associated with foundation works (149.6 kgCO2e/m2GIA) derive from new foundation piles as well as provisional piling to form a retaining wall on the site boundary that were necessary to allow excavations.
The CO2 emissions associated with the reinforced concrete frame superstructure are very high (203.3 kgCO2e/m2GIA), despite the use of low embodied carbon cement, also due partly to the height of the building (10 storeys). However, part of the reason for the high figures should be found in the rather ‘inefficient’ floor plan, which sought to maximise the number of rooms and leasable space and hence resulted in a higher quantity of structural materials used.
The CO2 emissions associated to the facades (52.2 kgCO2e/m2GIA) are average. This is due to the usage of aluminium panels for top-floor cladding and aluminium composite panels as rainscreen cladding for the rest of the building.
 

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Comparisons between research results and international benchmarks

A comparison with current benchmarks is provided in Figure 4, showing the four projects sit around the LETI 2020 (Band C) targets, which is considered by the authors to be a positive outcome.

Limitations and further work

 Impact of building services
Due to the difficulty in obtaining actcurate data from external consultants, the present study considered parametric incidence (kgCO2/m2 GIA) with regards to mechanical, electrical and plumbing (MEP). This approach can be considered limited and CIBSE recently published guidance to assist with detailed embodied carbon calculation for building services [4], [5]. The team is looking to implement this for the next studies.

Energy mixes in different countries
It is important to note that comparisons with international standards should consider the national differences in energy mix and consequently the variation on embodied carbon associated with manufacturing stages A1-A3 in different countries. The investigation of this aspect is beyond the scope of this study; however, the authors would welcome a collective effort towards the determination of national embodied benchmarks, similarly to what has been achieved by initiatives such as LETI in the UK.

Impact of seismic design
Also, important to note within the context of comparison with international standards is how seismic loads often govern building design in locations prone to seismic events [6], [7]. In such circumstances, structures are required to bear proper stiffness and load-bearing capacity to resist frequent earthquakes, and possess proper ductility and energy-dissipating capacity to avoid collapse, in case of rare more severe earthquakes. This results in greater sections of structural members and higher incidence of steel reinforcement which has a notable impact on embodied carbon figures associated with the building structure.

Climatic differences
Slight variations of embodied carbon values were also observed with the variation of climate area, from South European countries (Z1) to Central (Z2) and North European countries (Z3) [7]. This is outside the scope of the present research.
 

Conclusions

The study confirmed that, with the same GIA, the CO2 emissions corresponding to the complete refurbishment of building (even with a new floor on top or a new wing) are significantly lower than the emissions related to a new construction.
In fact, extending the service life of a building is one of the best strategies to reduce the CO2 emissions of the construction sector.
Such strategy (defined by LETI as “build less”) represent the background for the good results obtained for The Social Hub.
The second strategy is an optimization of the design of the structures, in order to reduce their volume and weight. This is the strategy used in the value engineering stage for the Hotel Porta Mascarella project, under evaluation.
The third strategy (not enough, as demonstrated by this paper, although necessary) is the optimization of material choice: low GWP materials with the same performances should be specified wherever possible, even if there is a small extra cost.
Such strategy (defined by LETI as “Reduce the use of high embodied carbon materials”) represent the background for the results obtained for Beyoo Student Housing.
The study demonstrates that the reuse and seismic improvement of the existing structures, where feasible, allow for a reduction of the CO2 emissions compared to the new construction, despite the even greater attention paid by Open Project in the design strategies and low GWP material specification.

References

[1]    WorldGBC, “Bringing embodied carbon upfront,” London, Sep. 2019. [Online]. Available: www.worldgbc.org/embodied-carbon
[2]    European Union, “Commission Delegated Regulation (EU) of 27.6.2023 supplementing Regulation (EU) 2020/852 of the European Parliament and of the Council by establishing the technical screening criteria for determining the conditions under which an economic activity qualifies as contributing substantially...and whether that economic activity causes no significant harm to any of the other environmental objectives and amending Delegated Regulation (EU) 2021/2178.” EU, Brussels, Jun. 27, 2023.
[3]    RICS, “Whole life carbon assessment for the built environment,” p. 41, 2017, [Online]. Available: http://www.rics.org/Global/Whole_life_carbon_assessment_for_the_BE_ PG_guidance_2017.pdf
[4]    CIBSE, Embodied carbon in building services: a calculation methodology. London: Chartered Institution of Building Services Engineers, 2021.
[5]    CIBSE, Embodied carbon in building services using the TM65 methodology outside the UK - CIBSE TM65LA: 2022. London: Chartered Institution of Building Services Engineers, 2022.
[6]    D. Trigaux, & K. Allacker, and & W. Debacker, “Environmental benchmarks for buildings: a critical literature review”, doi: 10.1007/s11367-020-01840-7/Published.
[7]    Dos Santos Gervasio, H. and Dimova, S., Environmental benchmarks for buildings, EUR 29145 EN, Publications Office of the European Union, 2018, ISBN 978-92-79-80969-9 (print),978-92-79-80970-5 (pdf), doi:10.2760/073513 (online),10.2760/90028 (print), JRC110085.

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