Exploring volumetric modular systems in residential construction

Andy Higson is business director at Intrastack, part of Saint-Gobain Off-Site Solutions

Volumetric modular construction has made significant progress from its humble roots in commercial projects like portable classrooms. These structures, often referred to as ‘The Mobile’, were simple, transportable boxes that minimised onsite construction and disruption.

In recent years, volumetric modular systems have entered the residential market with notable successes, such as the Ministry of Defence’s SLAM contract for single living accommodation. However, challenges have arisen as this method expanded into low-rise housing, particularly highlighted by the struggles of major volumetric manufacturers like Legal & General and Ilke Homes.

“Volumetric construction demands substantial upfront investment as the entire house is constructed in the factory before receiving payment”

Witnessing high-profile manufacturers of offsite builds struggle to operate a profitable business creates a misguided hesitation over its effectiveness as a viable alternative to traditional methods of construction, which I absolutely believe it is.

And many agree. A recent survey of the housebuilding industry by Housebuilder & Developer revealed that 72 per cent believe that housebuilders can save money by building offsite and 89 per cent agree that building offsite can positively affect housing supply.

So what role does volumetric modular construction play in the housebuilding sector, what challenges does it face, and how do they impact its future in residential housing?

Speed vs cost

There is a trade-off between the speed and cost of volumetric modular construction. Decision-makers must understand the available solutions and how they align with project needs.

While volumetric systems can be fast, they have added costs associated with them. Housing associations may accept these costs to provide affordable housing quickly, but national housebuilders may not prioritise speed and consider the added costs unnecessary.

Volumetric housing requires elements like carpets, kitchens and bathrooms to be pre-fitted, resulting in overengineering and increased costs. If you compare this with other methods of construction, such as traditional bricks and mortar or a panellised system where more work is done onsite, it only needs to have the strength to withstand the final building design.

Design limitations and placemaking

From a volumetric perspective, there are limitations in tailoring buildings to meet the specific needs of end users.

Volumetric modular houses often have long and narrow floor plans due to transportation constraints. Roof design is also limited by factors like tunnel clearance height, resulting in shallower roofs with minimal pitch.

This affects the aesthetics and architectural variety of volumetric constructions. In low-rise housing, creating visually captivating neighbourhoods that cater to residents’ needs is essential, requiring diverse designs and orientations. Consequently, if a more intricate design is desired, modular boxes may not offer the same flexibility as a panellised system.

Upfront costs and mortgage accessibility

Volumetric construction demands substantial upfront investment as the entire house is constructed in the factory before receiving payment. For large residential developments, the multiplied upfront costs per unit becomes a significant financial undertaking. Establishing effective payment and invoice structures is vital in managing this situation.

Due to its high level of premanufactured value, volumetric construction can benefit from the government’s strategic partnership grant by reaching the required 55 per cent premanufactured value threshold. It is also possible to achieve 55 per cent with panellised systems incorporating elements such as closed-panel construction, and staircases, roofs, or bathroom pods.

Decisions for design and finishes in volumetric construction must be made upfront, as changing them during production can disrupt the entire process.

Modular housing offers the advantage of design standardisation, which is beneficial for large-scale affordable housing projects.

However, achieving standardisation becomes challenging due to variations in elements like kitchens, brick finishes, roof finishes and windows. Maintaining stock levels of numerous products becomes crucial to prevent production delays.

Balancing manufacturing and financial considerations

Established volumetric providers have a better understanding of balancing commercial considerations and sustainable practices. As a result, they have backed away from the low-rise housing market and continued to focus on more profitable commercial markets, leaving the newer volumetric entrants to learn the larger, more expensive lessons.

Housebuilders must prioritise understanding the organisations they collaborate with and consider their longevity and future stability to prevent uninformed decisions regarding the most suitable approach.

The future for residential construction

The goal of delivering affordable residential solutions on a global scale remains important. Offsite manufacturers aim to bridge the affordable housing gap, but the credibility of the concept depends on choosing the right construction methods for each project. Traditional construction, elemental masonry solutions, light-gauge steel frames and hybrid approaches that combine panellised and volumetric elements are anticipated.

Housebuilders need to explore the full range of options beyond volumetric construction. Collaboration and expertise are vital factors in ensuring successful outcomes.

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