MMC: quality assurance

Thoroughly modern builders

17 April 2019

Recent years have seen an upsurge of interest in modern methods of construction as the UK strives to supply more new, high-quality homes, and building control bodies have a crucial role to play in assuring that quality

The increasing interest in modern methods of construction (MMC) is partly due to the publication of the Farmer Review, Modernise or die, in October 2016, and the Ministry of Housing, Communities & Local Government white paper, Fixing our broken housing market, published the following February. Coupled with the well-publicised shortage of skilled labour in the housing market, we are now seeing more housebuilders investigating new ways of building.

NHBC, for example, previously received between 4 and 8 innovative systems to review each year, but in recent years this number has risen dramatically, with more than 30 received in 2016 and a record of 42 submitted in 2018. To meet this rising demand, NHBC launched the MMC Hub in 2016, an online portal providing guidance and listing building systems accepted as meeting our standards.

The types of MMC system we see at NHBC are varied, and include traditional construction materials such as timber, steel and precast concrete as well as less common materials such as aerated concrete and cross-laminated timber, and occasionally innovations such as 3D printing and glass-fibre-reinforced materials.

We have also seen a change in the types of MMC submitted for review. Whereas 2 years ago most were on-site MMC systems – such as insulated concrete formwork and thin-bed mortar blocks – or panellised systems, there has been a shift towards more complex whole-house volumetric systems. The recent NHBC Foundation Report Modern methods of construction: who’s doing what? demonstrated the growing interest in and benefits of using MMC.

We have seen such interest before, but there are a number of new factors behind the current growth in the use of MMC. For a start, concern about skills shortages in housebuilding has driven up the cost of traditional trades, leading builders to explore alternative methods of construction. Then there are the opportunities that come from the use of new, viable technologies that help realise the potential of MMC.

Notably, however, it is the investment in off-site manufacture by housebuilders that shows the value that can be achieved using MMC. This move towards vertical integration by some of the major builders allows them to realise the benefits of MMC through procurement and direct management of the supply.

Image of a house that has been manufactured off site.

Figure 1: Assembling a house that has been manufactured off site: housebuilders are investing more in modern methods of construction, partly in response to skills shortages

Despite the growth in activity, NHBC’s rate of acceptance for these systems is not increasing. The main reason for this is because many simply fail to demonstrate that they meet our standards. Typically, we see 2 areas of concern:

  • the need for an early design freeze so that specification of components and proof of their performance can be fully demonstrated before manufacture begins; and
  • factory production controls – the biggest risk in off-site manufacture is that of systematic defects, so we require production to be carried out under an audited and approved quality management system.

Often the materials or technologies are not new, but where and how they are assembled is innovative. The change in sequence from traditional forms of construction means that interfaces are created that cannot be detailed by the usual methods, and new details need to be designed with regard to the buildability, structural stability, durability, acoustics, weatherproofing, performance in fire and thermal performance of the building.

As a result of the industry-wide increase in use of MMC, and whole-house volumetric systems in particular, there will be a need to adapt to the changes that the new processes bring, especially for everyone working in the building control sector. Whole-house volumetric system manufacturers will need to take greater ownership of the designs, production and site delivery process for the MMC systems.

The experience that NHBC Building Control has of whole-house volumetric systems to date clearly identifies there is an opportunity for building control bodies (BCBs) to use their expertise and knowledge to work alongside manufacturers and ensure compliance with warranties and the Building Regulations before delivery to site.

BCBs will need to consider whether manufacturers have the right level of in-house expertise and controls in place on the production line and on site to enable this. BCBs would also be wise to consider reviewing their operating procedures and approach before dealing with volumetric systems, since the technical information and building control compliance package would ideally need to be scrutinised before production commences in the factory.

This highlights the importance of engaging with the manufacturer and the builder before production starts. Engagement at this stage will ensure that a detailed, early technical review is carried out with building control so no further changes are made to the working drawings and specifications. Early involvement with BCBs also reduces the chance of the product being delivered when not fully compliant with the Building Regulations, and limits the risk of having to rectify non-compliant features later on site. Ensuring compliance is highly dependent as well on the manufacturing programme keeping to the agreed plans and specifications reviewed by the BCB.

Another important function of early engagement between the design team and BCB is establishing a suitable inspection regime. This will ensure each home built using MMC systems has an inspection record that covers the process from off-site manufacturing to delivery on site and installation, allowing a final certificate to be issued. A challenge that may need to be taken into account by BCBs is factory production and the location of the factory. The production line might be hundreds of miles from the construction site, so BCBs might consider it necessary to carry out ad hoc or planned inspections in the factory as well as site inspections to ensure production complies with the agreed specification.

NHBC is geared up to support the industry as it moves to diversify the methods for building homes. But while we support innovation, it must be responsible, and its performance proven for all elements of the home. All involved in the design, procurement, manufacture and building of MMC systems should acknowledge the extent of information required to demonstrate compliance; this will often need to be concluded at an earlier stage than for conventional construction since the technical design and manufacturing controls need to be reviewed and accepted before manufacture begins. Successful MMC systems have invested extensive resources in developing the design of both the product and manufacturing processes.

With responsible innovation, new homes can be built to high standards, supporting NHBC’s core purpose to give homeowners confidence in their quality.

Richard Lankshear is innovation manager and Paul Williams is technical operations manager at NHBC

Further information