How Offsite Construction Bring Solutions for Sustainable Buildings?

Moad Ziadi, Project Management Director Europe, Unibail Rodamco Westfield

Offsite construction, even if it is part of the Modern Methods of Construction (MMC), remains an old technology which at the latest had emerged at the beginning of the 20th century. In the United States, some real estate companies started selling ‘Kit houses’ in the 1900s. The associated technology and its own standards framework were the embryo of what we now call modern offsite construction.

This technology takes many forms, ranging from a 3-dimensional module such as prefabricated hotel bathrooms or student bedroom modules to simple elements such as precast slabs, masonry blocks or even non-structural assemblies and sub-assemblies such as electrical boards or mechanical boxes.

The objective of this technology, at the beginning of the last century, was to find solutions to build quickly and guarantee better or at least identical quality to the classical construction method.

In fact, the offsite construction had a spectacular boom in Europe after the Second World War and this technology success was maintained more than two decades after to build more housing for about 1 million Pieds-Noirs evacuated from Algeria to mainland France. The baby boom, population growth and successive waves of foreign workers have maintained the shortage of housing demand and pushed the offsite construction industry to keep developing in France and generally in Europe.

Today, it should be reminded that the volume of the offsite construction industry - according to a report performed by McKinsey - will reach a size of 130 billion dollars by 2030 in Europe and the United States.

It is then time for all the actors, project owners, architects, engineers, and contractors to start organizing themselves to take useful advantage of this developing industry and ensure that this opportunity will not be missed especially on the aspects related to sustainability.

In fact, climate change and the challenges of sustainability have today given rise to a new virtue in offsite construction, that of reducing the carbon footprint and reducing the energy consumed by buildings.

It should be reminded that industry is responsible for 40% of greenhouse gas emissions, the construction industry holds a good part of this percentage. Likewise, 20% of greenhouse gases come from the use of buildings (housing and services) because it uses fossil fuels and electricity.

Offsite construction comes with solutions to these two problems, namely the reduction of the carbon footprint but also the energy consumed by the buildings.

"It is time for actors, project owners, architects, engineers, and contractors to start organizing themselves to take advantage of this developing industry and ensure that this opportunity will not be missed especially on the aspects related to sustainability."

The first factor that contributes to this advantage is the design, because the offsite construction considers an industrialization approach, the design is therefore optimized and reduces the oversizing linked to the onsite construction context, likewise this process allows frugality and flexibility to be favored and then less material is used and disassembly is facilitated, allowing better management of life cycle.

Offsite construction requires less site equipment for propping and scaffolding, this saves hours of labor equipment mounting dismounting and transportation. It accelerates the work schedule to start all the trades quickly after performing the structural and façade works.

According to a study performed by HLM architects, who has several references in housing projects under offsite construction, the structure is optimized to approximately 30% less concrete and steel frame materials.

The industrialization of building enclosure works using unitized façade is also an important field of the offsite construction, it allows to relocate units from the factory area to the site for quick set up using a ready to use fixings. This process makes it possible to design facades with good insulation, good glazing optimizing sunshine and thereby reducing the energy consumed by buildings.

The second factor is the site itself, a 7,000 m² housing project in the heart of Paris in Montparnasse developed by URW was designed and built with prefabricated wooden elements. This solution saved 56% of the weight of the structure compared to a traditional solution thus saving on the quantities of structure and on the volume of the foundations, the on-site works schedule is reduced by 40% compared to a traditional solution and therefore the indirect worksite running costs including the consumption of electricity, water but also the transport of workers to the site have also been reduced.

On top of that, the factories make fewer losses than the construction sites, for the same design there are at least 4 times less losses in the factory than on the construction site.

On the Montparnasse operation in Paris, we have recorded that for direct labor, this solution reduced the number of workers on site by up to 70% and offered the neighborhood a less harmful site in terms of noise, dust but also delivery traffic, which has been reduced by almost half, thus contributing to a reduction in the site's transportation carbon footprint.

Offsite construction factories offer a potential energy advantage that the construction site cannot offer, indeed in terms of the energy mix specific to factories, it makes it possible to reduce the carbon footprint of its own products by developing geothermal energy, solar energy or by taking advantage of any non-stored energy from other activities or yielding the excess energy produced by the factory plant to other activities. Two ArcelorMittal plants in Spain and Germany have been able to significantly decarbonize structural products thanks to the proper management of the energy balance of these production units.

In short, offsite construction can reduce the carbon footprint of projects by 50%, the experience of the United Kingdom's national education department recorded a rate of 260 kgCO2e/m² instead of 540 kg CO2e/m² for a school building program.

Today with the housing shortage in Europe, the offsite construction is the process that both answers this problem while also offering an innovative sustainable perspective.

The other building sectors, office, retail, logistics, and other public and private buildings should also jump to the pool and try to create the appropriate mechanisms to take advantage of the offsite construction because it's not just a luxury, it's a necessity.