MMC may evolve over time – but the challenges remain the same 

Stuart Green is a professor of construction management at the University of Reading.

The large panel system (LPS) has recently been in the news, sparking much nostalgia among those of a certain age.

Concerns are growing about the safety of high-rise housing blocks built during the 1950s and 1960s using LPS. The Building Safety Regulator is reportedly prioritising LPS buildings following the partial evacuation of Barton House in Bristol in November 2023 over fire-safety concerns.

“Buildings are best understood as long-term assets whose success cannot be judged solely at the point of practical completion”

The problem apparently relates to a lack of structural ties between the floors and the load-bearing external walls. Hence memories go back to the gas explosion that caused the partial collapse of the 22-storey Ronan Point tower block in east London on 16 May 1968.

Ronan Point was constructed by Taylor Woodrow-Anglian using a licensed LPS variant known as Larsen Nielsen. It was heralded at the time as a pioneering modern method of construction (MMC). In essence, the approach comprised factory-made precast concrete panels bolted together on site. In today’s nomenclature it would be classified as MMC Category 2. But MMC is more meaningfully understood as a flexible narrative that evolves over time rather than a static concept that lends itself to precise definition.

By the late 1960s more than 30,000 tower blocks had been constructed throughout the UK using LPS variants. Massive state sponsorship of public housing made it economic for contracting firms to invest in offsite prefabrication factories. The subsequent withdrawal of the state from the provision of mass housing means that modern contractors often lack the equivalent incentive for investment. They wisely prefer to employ client-facing advisors in sharp suits while offsetting the capital risk to others.

LPS buildings such as Ronan Point had an initial life expectancy of 60 years. Hence it is not surprising that they now require remedial work. However, many such buildings were demolished within 15 years due to rapidly escalating maintenance costs. The full details of the construction defects within Ronan Point only emerged following its forensic demolition in 1986.

The identified flaws were truly shocking. Extensive defects were found in the joints between panels, and especially in the joints between panels and floors. Problems included unattached fixing straps and levelling nuts not being tightened, hence causing loads to be transmitted via the bolts. Some of the panel/floor joints were found to contain less than half of the mortar specified, with voids packed with newspaper. Disturbingly, some of the recovered newspapers dated from the remedial work that followed the initial 1968 partial collapse.

For all the talk of precision engineering, the prefabricated concrete panels were too often installed onsite by largely unskilled labour, incentivised to ensure speed of construction. Onsite supervision and independent inspection were sadly lacking.

Changing times?

Of course, such problems should never happen today. Yet they do. The current advocates of MMC (however defined) talk a lot about factory-based precision engineering, but rather less about what happens when the prefabricated components arrive onsite. Too often we get little other than blasé references to “bolting the modules together”. Some cases suggest a similar failing of onsite supervision. And sadly, the over-hyped legitimising narrative of MMC is directly implicated. Concerns relate especially to the fire-stopping in the vertical and horizontal cavities between modules.

The precise identities of those responsible for onsite installation are often difficult to ascertain, and the extent of their competence to perform the assigned tasks remains shrouded in mystery. Given the ongoing vagaries of demand, there is a widespread temptation to rely on contingent labour for the purposes of onsite installation.

MMC is, of course, not only about volumetric methods, and there are many acclaimed success stories. It is therefore important not to throw the baby out with the bathwater.

The long history of prefabrication contains numerous examples of both successes and failures. Buildings are best understood as long-term assets whose success cannot be judged solely at the point of practical completion. They can only meaningfully be evaluated in terms of through-life performance.

Looking forward, we should indeed celebrate the successes while striving to avoid the failures. Nevertheless, the continued dichotomisation between the ‘modern’ and the ‘traditional’ stands in the way of meaningful progress. Getting the joints right between prefabricated components is in essence a very traditional problem.

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