Joint interview: ecodesign applied to off-site construction

Forward-planning, cost control and performance management: the specific expertise and benefits of off-site construction are also an opportunity to improve a building’s environmental footprint. The design phase is longer and more important, which means that solutions that promote energy efficiency, recycling and the use of low-impact raw materials can be factored in upstream of a project, when these decisions have the most impact. David Damichey from Cubik-Home and Bruno Peuportier from MINES Paris PSL talked to us in this joint interview.

1. What are the benefits of off-site construction for customers and for the environment?

David Damichey: Cubik-Home produces three-dimensional concrete modules off-site. Each one measures up to 10 metres in length and 4 metres in width. The modules are partially or fully prefabricated in our plant and are assembled horizontally and vertically for two-floor buildings right now. This will be expanded to three-floor buildings in the near future and will ultimately be rolled out for constructions with up to eight floors.

The advantages of this process derive from a remote technical platform, which offers a range of personalisation options and reflects the image of a solid property. We are aware that concrete is criticised for its environmental impact. We strive to turn this into a strength by working with next-generation concretes. Consumers are increasingly receptive to a reduction in products’ long-term carbon footprints, via the circular economy.

In addition, time constraints have risen in line with customers’ level of expectation. The desire to own property now comes by browsing on a tablet. Speaking of time constraints, off-site construction is an obvious way of cutting construction times as off-site processes allow for forward planning. In terms of quality, the Cubik-Home method brings about improved overall cost control and performance management thanks to more in-depth preliminary studies.

Bruno Peuportier: Mass production means that more time can be spent on studies in the design phase, compared to small-scale building projects. This is the phase in which the most impactful decisions are made regarding the building’s environmental performance. The design can therefore be optimised, and even personalised depending on what the project owner wants.

Off-site construction provides enhanced quality control thanks to the work environment and production checks. This is particularly true for features such as thermal insulation and airtightness. There is also more scope for recycling.

Pooling resources over a large number of buildings also helps in the selection of suppliers, for example for low-carbon cements, recycled steel, construction components and fittings. This selection process includes environmental criteria.

2. Which scientific and business-specific challenges are met by the collaborative project between Cubik-Home and MINES Paris Psl, launched as part of the lab’s Research & Solutions programme?

Bruno Peuportier: For our research team, it was interesting to model an innovative industrial process including inputs and outputs, and in particular water and energy consumption, as well as waste. Defining an appropriate benchmark to which the product can be compared as part of a life cycle assessment raised a few questions. Should we consider parameters that are completely identical? How should conventional materials be selected? Can a standard construction site be defined? Are all usage scenarios the same? Which assumptions should be considered for the end of the life cycle?

The most motivating aspect of this type of research is definitely having to identify avenues for improvement. We had to review the choice of materials, components and equipment, and study material-saving options, the way in which the various elements can interact to reduce consumption and impact while ensuring a high level of comfort.

David Damichey: When you are creating an innovative industrial solution, it is difficult to rely on existing life cycle assessment benchmarks. As we have always been interested in these aspects, we probably could have moved forwards ourselves if we had more time. However, to adopt a method that quickly leads to the definition of relevant levers and indicators, working with experts in this field was an obvious choice for us.

It is always possible to adapt a production line to make it more efficient, but this is inevitably more expensive than adopting good practices upstream. During a discussion with VINCI employees, I asked them to put me in touch with the MINES Paris PSL Research Centre for Energy Efficiency of Systems. Our first contacts were very surprising, as we did not speak the same language, but we all made an effort to understand each other and the fact that we took part in the webinar on 11 May is a testament to its success.

3. There are many stages in the life cycle assessment. It therefore considers impacts related to the building’s construction, use, renovation and demolition phases. Which of these phases has the most impact in terms of CO2 emissions and which actions will be rolled out to mitigate this impact?

Bruno Peuportier: As with most buildings and estimating a life span of 100 years, the main contributions to impacts are found in the building’s use phase (heating, domestic hot water, electricity, drinking water production and waste water treatment). Improving energy performance, with, for example, the use of a geothermal heat pump, reduces this contribution and gives greater importance to building materials, although the share related to these products can be cut by using lower-impact materials.

David Damichey: As Bruno said, the main contribution to the building’s footprint is in the use phase. However, our role as a committed industrial player is not to remain a spectator, but to take action on our level to mitigate the impacts of the process and the product. Let’s not forget that the most inexpensive energy and resources are those we don’t consume. A building with a more efficient and intelligent envelope has fewer energy requirements, thereby preserving resources. From the outset, we strove to reduce the thickness of the walls and slabs which are 5 and 7 cm thick respectively.

We were thinking of working with lower-carbon, bio-sourced materials, but this move came more quickly thanks to our collaborative work with the Mines research centre. To give but a few examples, we are now using Cem III cement to produce the modules. This next-generation cement has even become a replacement and has been extended to all Francioli’s production. In the future, we are also going to use bio-sourced materials for insulation and fittings.

4. Which research and development prospects are open to Cubik-Home to go even further with its environmental goals?

Bruno Peuportier:
To leverage the proposed concept most effectively, the option of using foundations (stakes) to power a geothermal heat pump needs to be studied in greater depth. The aim is to develop expertise to roll out this solution on its most appropriate scale, and to assess performance more precisely. Other improvements may be explored such as the option of using bio-sourced fibres instead of steel. Ultimately, the goal is to achieve a carbon-neutral solution, without shifting the impact to health, biodiversity or resources.

David Damichey: Off-site construction addresses the question of building differently with beneficial effects for environmental objectives, such as a better use of resources and their reduced consumption in construction. This also applies to waste production, as there is less waste than on a conventional building site. The market is clearly developing and offers strong potential for meeting carbon reduction targets.

As we are currently at the stage of pre-series production, we are focusing on the product’s economic and environmental optimisation. Without wanting to disclose our ambitions, a building that remains movable over time offers many advantages in terms of the circular economy.

Off-site construction will not replace conventional construction, but it will round off the range of available solutions by developing industrial prefabrication tools.

For further information, you can watch the replay of the Research & Solutions webinar on “The environmental opportunities of off-site construction” with David Damichey and Bruno Peuportier (in French).

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Life-cycle assessment is a method to assess the environmental impacts of buildings and infrastructures throughout their life cycle, from the extraction of raw materials through to their end-of-lifetime handling.
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