Richard Smith of NHBC looks at lessons from the history of Modern Methods of Construction, and how the growth of offsite is being driven by the combined forces of housing shortages, the need for quality, and climate change.

Modern Methods of Construction (MMC) have been considered the future of house building for some time. Yet, excluding Scotland, most new homes in the UK are still brick and block and factory-built housing remains uncommon.

The promised benefits of non-traditional and offsite construction are well documented: speed of onsite operations, fabrication quality, safer working conditions, material efficiency and reduced waste, and less noise and disruption for residents. However, enthusiasm for non-traditional construction methods has been anything but consistent. 

Today, at a time of increased housing need and a country-wide skills shortage, the case for non-traditional housing is being made again. By looking back at the development of MMC we can learn lessons, make continuous improvement, and harness technological advances, such as digitally enabled design, to deliver high-quality, economical factory-made homes. 

LOOKING BACK

There have been three previous periods of advancement in non-traditional house building techniques: after the First World War when there was a serious shortage of skilled labour, essential materials and industrial capacity the large-scale building campaigns seeking to provide homes after the Second World War combined with the Government programme to replace slum housing the shift towards industrialised building and high-rise construction during the house building boom of the 1960s and 1970s.

Interestingly each of these periods of development and Government-stimulated investment have been followed by a return to traditional techniques. There is no single reason for this, except the problem of mass production always applies – make a mistake once and you make it many times rapidly, so it becomes expensive to remedy.

However, there was extensive non-traditional housing output in the 1960s when government-promoted factory-built housing delivered in quantity, providing numerous homes. Unfortunately, much less emphasis was placed on quality and how housing at scale would integrate into the wider area and infrastructure, leading to a lasting negative perception. 

LOOKING AHEAD

That is why, regardless of how homes are built, good practice principles of neighbourhood planning, housing design and construction detailing should be followed.

Promising systems made from various materials have been developed out of the early experiments, wider applications and specific innovations of the last century. But MMC alone does not guarantee fabrication quality. 

Again, design underpins everything and investment at the early stages of a project can mitigate the risks of off-site construction. Detailed drawings and specification of all components, beyond that required in conventional construction, are also essential before manufacture begins.

Although prefabrication reduces time on site, care is still required for site operations that cannot be transferred to a factory. Indeed, where traditional construction interfaces with precise factory-assembled components, such as at the junction of the external walls and ground floor, it must be built to tighter tolerances. 

Quality assurance checks by a third party are therefore key. Checks must take place throughout before products leave the factory, once they are installed on site and on the remaining site operations. 

CONTINUOUS IMPROVEMENT

Anyone designing or commissioning off-site construction can work towards continuous improvement in MMC and should consider the implications of the need for investment in design, the choice and design of systems and site operations. And, of course, standards need to continue to adapt to meet the demand from industry. These areas are explored in the below paragraphs.

INVESTMENT IN DESIGN

Design should be based on established good practice principles regardless of how homes are constructed. Rigorous detailed design, resolving construction details and specifying all components is essential before manufacture can commence Lastly, a Quality Management System for MMC which is audited by a third party is essential to ensure good design.

CHOICE OF SYSTEM

When it comes to the difficult choice of which MMC system to opt for, the first priority is to choose the most appropriate construction solution for site constraints and planning requirements. You also need to understand and work with the characteristics and the limitations of different materials and technologies. 

It’s important to test material assemblies as a complete system (for performance and durability as well as manufacturing operations). Also, prototype and test to investigate performance over wide ranging and seasonal variations (including extreme weather effects of climate change) and for the expected lifespan of products. Lastly, it’s key to build in realistic tolerances to allow systems to be effectively and efficiently assembled.

SITE OPERATIONS

It’s important to be aware here that manufacturer assurances and warranties do not remove the need for site supervision and checks. Consider sequence of assembly and allow for visual inspection of key construction details. 

Other site-based factors that need bearing in mind are protecting the structure from changing weather conditions during assembly, and the need to build groundworks to tighter tolerances which will readily accept precisely engineered modules or panels.

CONSIDERING DIFFERENT APPROACHES

Sadly, there is no MMC method or material that is suitable for all sites and all building types.

Careful choices must be made between tried and tested traditional techniques and numerous innovative systems, considering both the general benefits of offsite construction and inherent characteristics depending on the material used. The suitability of different construction approaches or the combination of diverse technologies will depend on many factors. However, there are some recognisable affinities between the approaches and common site constraints as well as project types or tenures.

With this in mind, there is no shortcut when commissioning and designing off-site construction systems. Early investment in design, appropriate choice of system and oversight of onsite operations is critical to deliver high-quality, long-lasting and stylish homes that meet the needs of their occupants. 

If the lessons of the past are learned – basic good practice construction detailing is followed, a standard template is used but homes are responsive to their environment, and systems build upon and employ existing prefabricated building components – factory-built homes can benefit the industry, help address the housing crisis and contribute to tackling the climate emergency.

To find out more download the free NHBC Foundation report on ‘Modern methods of construction: Building on experience’ by scanning the QR Code. 

Richard Smith is head of standards, innovation & research at NHBC